Network Working Group J. Strassner Internet Draft Huawei Technologies Intended status: Standard Track J. Halpern Expires: November 30, 2017 S. van der Meer Ericsson May 30, 2017 Generic Policy Information Model for Simplified Use of Policy Abstractions (SUPA) draft-ietf-supa-generic-policy-info-model-03 Abstract This document defines an information model for representing policies using a common extensible framework that is independent of language, protocol, repository. It is also independent of the level of abstraction of the content and meaning of a policy. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on November 30, 2017. Copyright Notice Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Strassner, et al. Expires November 30, 2017 [Page 1]
Internet-Draft SUPA Generic Policy Model May 2017 Table of Contents 1. Overview ....................................................... 9 1.1. Introduction .............................................. 9 1.2. Changes Since Version -03 ................................ 11 2. Conventions Used in This Document ............................. 11 3. Terminology ................................................... 12 3.1. Acronyms ................................................. 12 3.2. Definitions .............................................. 12 3.2.1. Core Terminology .................................... 12 3.2.1.1. Information Model .............................. 12 3.2.1.2. Data Model ..................................... 13 3.2.1.3. Class .......................................... 13 3.2.1.3.1. Abstract Class ............................... 13 3.2.1.3.2. Concrete Class ............................... 13 3.2.1.4. Container ...................................... 13 3.2.1.5. PolicyContainer ................................ 13 3.2.2. Policy Terminology .................................. 14 3.2.2.1. SUPAPolicyObject ............................... 14 3.2.2.2. SUPAPolicy ..................................... 14 3.2.2.3. SUPAPolicyClause ............................... 14 3.2.2.4. SUPAECAPolicyRule .............................. 15 3.2.2.5. SUPAMetadata ................................... 15 3.2.2.6. SUPAPolicyTarget ............................... 15 3.2.2.7. SUPAPolicySource ............................... 15 3.2.3. Modeling Terminology ................................ 16 3.2.3.1. Inheritance .................................... 16 3.2.3.2. Relationship ................................... 16 3.2.3.3. Association .................................... 17 3.2.3.4. Aggregation .................................... 17 3.2.3.5. Composition .................................... 17 3.2.3.6. Association Class .............................. 17 3.2.3.7. Multiplicity ................................... 18 3.2.3.8. Navigability ................................... 18 3.3. Symbology ................................................ 18 3.3.1. Inheritance ......................................... 18 3.3.2. Association ......................................... 19 3.3.3. Aggregation ......................................... 19 3.3.4. Composition ......................................... 19 3.3.5. Association Class ................................... 19 3.3.6. Abstract vs. Concrete Classes ....................... 20 4. Policy Abstraction Architecture ............................... 21 4.1. Motivation ............................................... 22 4.2. SUPA Approach ............................................ 23 4.2.1. Design Patterns ..................................... 23 4.2.1.1. Composite Pattern .............................. 24 4.2.1.2. Decorator Pattern .............................. 24 4.2.2. Association Classes ................................. 26 Strassner, et al. Expires November 30, 2017 [Page 2]
Internet-Draft SUPA Generic Policy Model May 2017 Table of Contents (continued) 4.3. SUPA Generic Policy Information Model Overview............ 27 4.3.1. SUPAPolicyObject .................................... 29 4.3.2. SUPAPolicyStructure ................................. 30 4.3.3. SUPAPolicyComponentStructure ........................ 30 4.3.4. SUPAPolicyClause .................................... 31 4.3.5. SUPAPolicyClauseComponentDecorator .................. 31 4.3.6. SUPAPolicyTarget .................................... 32 4.3.7. SUPAPolicySource .................................... 32 4.4. The Design of the GPIM ................................... 32 4.4.1. Structure of Policies ............................... 33 4.4.2. Representing an ECA Policy Rule ..................... 34 4.4.3. Creating SUPA Policy Clauses ........................ 37 4.4.4. Creating SUPAPolicyClauses .......................... 41 4.4.5. SUPAPolicySources ................................... 42 4.4.6. SUPAPolicyTargets ................................... 43 4.4.7. SUPAPolicyMetadata .................................. 43 4.4.7.1. Motivation ..................................... 44 4.4.7.2. Design Approach ................................ 45 4.4.7.2.1. Policies and Actors ....................... 46 4.4.7.2.2. Deployment vs. Execution of Policies ...... 47 4.4.7.2.3. Using SUPAMetadata for Policy Deployment and Execution ............................. 47 4.4.7.3. Structure of SUPAPolicyMetadata ................ 48 5. GPIM Model .................................................... 52 5.1. Overview ................................................. 52 5.2. The Abstract Class "SUPAPolicyObject" .................... 53 5.2.1. SUPAPolicyObject Attributes ......................... 54 5.2.1.1. Object Identifiers ............................. 54 5.2.1.2. The Attribute "supaPolObjIDContent" ............ 55 5.2.1.3. The Attribute "supaPolObjIDEncoding" ........... 55 5.2.1.4. The Attribute "supaPolicyDescription" .......... 55 5.2.1.5. The Attribute "supaPolicyName" ................. 55 5.2.2. SUPAPolicy Relationships ............................ 56 5.2.2.1. The Relationship "SUPAHasPolicyMetadata" ....... 56 5.2.2.2. The Association Class "SUPAHasPolicyMetadataDetail" .................. 56 5.3. The Abstract Class "SUPAPolicyStructure" ................. 56 5.3.1. SUPAPolicyStructure Attributes ...................... 57 5.3.1.1. The Attribute "supaPolAdminStatus" ............. 57 5.3.1.2. The Attribute "supaPolContinuumLevel" .......... 57 5.3.1.3. The Attribute "supaPolDeployStatus" ............ 58 5.3.1.4. The Attribute "supaPolExecFailStrategy" ........ 58 5.3.2. SUPAPolicyStructure Relationships ................... 59 5.3.2.1. The Aggregation "SUPAHasPolicySource" .......... 59 5.3.2.2. The Association Class "SUPAHasPolicySourceDetail" .................... 59 5.3.2.2.1. The Attribute "supaPolSrcIsAuthenticated" . 59 5.3.2.2.2. The Attribute "supaPolSrcIsTrusted" ....... 59 Strassner, et al. Expires November 30, 2017 [Page 3]
Internet-Draft SUPA Generic Policy Model May 2017 Table of Contents (continued) 5.3.2.3. The Aggregation "SUPAHasPolicyTarget" .......... 59 5.3.2.4. The Association Class "SUPAHasPolicyTargetDetail" ................... 60 5.3.2.4.1. The Attribute "supaPolTgtIsAuthenticated" . 60 5.3.2.4.2. The Attribute "supaPolTgtIsEnabled" ....... 60 5.3.2.5. The Association "SUPAHasPolExecFailTakeAction" . 60 5.3.2.6. The Association Class "SUPAHasPolExecFailTakeActionDetail" ........... 61 5.3.2.6.1. The Attribute "supaPolExecFailActionEncoding" ........... 61 5.3.2.6.2. The Attribute "supaPolExecFailActionName[1..n]" ......... 62 5.3.2.7. The Aggregation "SUPAHasPolicyClause" .......... 62 5.3.2.8. The Association Class "SUPAHasPolicyClauseDetail" .................... 63 5.4. The Abstract Class "SUPAPolicyComponentStructure" ........ 63 5.4.1. SUPAPolicyComponentStructure Attributes ............. 63 5.4.2. SUPAPolicyComponentStructure Relationships .......... 63 5.5. The Abstract Class "SUPAPolicyClause" .................... 64 5.5.1. SUPAPolicyClause Attributes ......................... 65 5.5.1.1. The Attribute "supaPolClauseDeployStatus" ...... 65 5.5.2. SUPAPolicyClause Relationships ...................... 65 5.5.2.1. The Aggregation "SUPAPolicyClauseHasDecorator" . 66 5.5.2.2. The Association Class "SUPAPolicyClauseHasDecoratorDetail" ........... 66 5.5.2.2.1. The Attribute "supaPolClauseDecConstraintEncoding" ...... 66 5.5.2.2.2. The Attribute "supaPolClauseDecConstraint[0..n]" ........ 66 5.6. The Concrete Class "SUPAEncodedClause" ................... 67 5.6.1. SUPAEncodedClause Attributes ........................ 67 5.6.1.1. The Attribute "supaEncodedClauseContent" ....... 68 5.6.1.2. The Attribute "supaEncodedClauseEncoding" ...... 68 5.6.1.3. The Attribute "supaEncodedClauseLanguage" ...... 68 5.6.1.4. The Attribute "supaEncodedClauseResponse" ...... 69 5.6.2. SUPAEncodedClause Relationships ..................... 69 5.7. The Abstract Class "SUPAPolicyClauseComponentDecorator ... 69 5.7.1. SUPAPolicyClauseComponentDecorator Attributes ....... 70 5.7.1.1. The Attribute "supaPolClauseConstraintEncoding" 70 5.7.1.2. The Attribute "supaPolClauseConstraint[0..n]" .. 71 5.7.2. SUPAPolicyClauseComponentDecorator Relationships .... 71 5.7.3. Illustration of Constraints in the Decorator Pattern 71 5.8. The Abstract Class "SUPAPolicyTerm" ...................... 72 5.8.1. SUPAPolicyTerm Attributes ........................... 73 5.8.1.1. The Attribute "supaPolTermIsNegated" ........... 73 5.8.2. SUPAPolicyTerm Relationships ........................ 73 Strassner, et al. Expires November 30, 2017 [Page 4]
Internet-Draft SUPA Generic Policy Model May 2017 Table of Contents (continued) 5.9. The Concrete Class "SUPAPolicyVariable" .................. 74 5.9.1. Problems with the RFC3460 Version of PolicyVariable . 74 5.9.2. SUPAPolicyVariable Attributes ....................... 74 5.9.2.1. The Attribute "supaPolVarName" ................. 74 5.9.3. SUPAPolicyVariable Relationships .................... 75 5.10. The Concrete Class "SUPAPolicyOperator" ................. 75 5.10.1. Problems with the RFC3460 Version .................. 75 5.10.2. SUPAPolicyOperator Attributes ...................... 75 5.10.2.1. The Attribute "supaPolOpType" ................. 75 5.10.3. SUPAPolicyOperator Relationships ................... 76 5.11. The Concrete Class "SUPAPolicyValue" .................... 76 5.11.1. Problems with the RFC3460 Version of PolicyValue ... 77 5.11.2. SUPAPolicyValue Attributes ......................... 77 5.11.2.1. The Attribute "supaPolValContent[0..n]" ....... 77 5.11.2.2. The Attribute "supaPolValEncoding" ............ 77 5.11.3. SUPAPolicyValue Relationships ...................... 78 5.12. The Concrete Class "SUPAGenericDecoratedComponent" ...... 78 5.12.1. SUPAGenericDecoratedComponent Attributes ........... 78 5.12.1.1. The Attribute "supaGenericDecoratedCompContent[0..n]" ....... 79 5.12.1.2. The Attribute "supaGenericDecoratedCompEncoding" ............ 79 5.12.2. SUPAGenericDecoratedComponent Relationships ........ 79 5.13. The Concrete Class "SUPAPolicyCollection" ............... 80 5.13.1. Motivation ......................................... 80 5.13.2. Solution ........................................... 80 5.13.3. SUPAPolicyCollection Attributes .................... 81 5.13.3.1. The Attribute "supaPolCollectionContent[0..n]" 81 5.13.3.2. The Attribute "supaPolCollectionEncoding" ..... 81 5.13.3.3. The Attribute "supaPolCollectionFunction" ..... 81 5.13.3.4. The Attribute "supaPolCollectionIsOrdered" .... 82 5.13.3.5. The Attribute "supaPolCollectionType" ......... 82 5.13.4. SUPAPolicyCollection Relationships ................. 83 5.14. The Abstract Class "SUPAPolicyComponentDecorator ........ 83 5.14.1. SUPAPolicyComponentDecorator Attributes ............ 84 5.14.1.1. The Attribute "supaPolCompConstraintEncoding" . 84 5.14.1.2. The Attribute "supaPolCompConstraint[0..n]" ... 85 5.14.2. SUPAPolicyComponentDecorator Relationships ......... 85 5.14.2.1. The Aggregation "SUPAHasDecoratedPolicyComponent" ............. 85 5.14.2.2. The Association Class "SUPAHasDecoratedPolicyComponentDetail" ....... 85 5.14.2.1.1. The Attribute "supaPolCompConstraintEncoding" .......... 86 5.14.2.1.2. The Attribute "supaPolCompConstraint[0..n]" ............ 86 Strassner, et al. Expires November 30, 2017 [Page 5]
Internet-Draft SUPA Generic Policy Model May 2017 Table of Contents (continued) 5.15. The Concrete Class "SUPAPolicySource" .................... 86 5.15.1. SUPAPolicySource Attributes ........................ 86 5.15.2. SUPAPolicySource Relationships ..................... 87 5.16. The Concrete Class "SUPAPolicyTarget" ................... 87 5.16.1. SUPAPolicyTarget Attributes ........................ 87 5.16.2. SUPAPolicyTarget Relationships ..................... 87 5.17. The Abstract Class "SUPAPolicyMetadata" ................. 88 5.17.1. SUPAPolicyMetadata Attributes ...................... 89 5.17.1.1. The Attribute "supaPolMetadataDescription" .... 89 5.17.1.2. The Attribute "supaPolMetadataIDContent" ...... 89 5.17.1.3. The Attribute "supaPolMetadataIDEncoding" ..... 89 5.17.1.4. The Attribute "supaPolMetadataName" ........... 90 5.17.2. SUPAPolicyMetadata Relationships ................... 90 5.17.2.1. The Aggregation "SUPAHasPolicyMetadata" ....... 90 5.17.2.2. The Association Class "SUPAHasPolicyMetadataDetail" ................. 90 5.17.2.2.1. The Attribute "supaPolMetadataConstraintEncoding" ...... 90 5.17.2.2.2. The Attribute "supaPolMetadataConstraint[0..n]" ........ 91 5.17.2.2.3. The Attribute "supaPolMetadataIsApplicable" ............ 91 5.18. The Concrete Class "SUPAPolicyConcreteMetadata" ......... 91 5.18.1. SUPAPolicyConcreteMetadata Attributes .............. 91 5.18.1.1. The Attribute "supaPolMDValidPeriodEnd" ...... 92 5.18.1.2. The Attribute "supaPolMDValidPeriodStart" .... 92 5.18.2. SUPAPolicyConcreteMetadata Relationships ........... 92 5.19. The Abstract Class "SUPAPolicyMetadataDecorator" ........ 92 5.19.1. SUPAPolicyMetadataDecorator Attributes ............. 92 5.19.2. SUPAPolicyMetadataDecorator Relationships .......... 92 5.19.2.1. The Aggregation "SUPAHasMetadataDecorator" .... 92 5.19.2.2. The Association Class "SUPAHasMetadataDecoratorDetail" .............. 93 5.19.2.2.1. The Attribute "supaPolMetadataConstraintEncoding" ...... 93 5.19.2.2.2. The Attribute "supaPolMetadataConstraint[0..n]" ........ 94 5.19.2.2.3. The Attribute "supaPolMetadataDecIsApplicable" ......... 94 5.20. The Concrete Class "SUPAPolicyAccessMetadataDef" ........ 94 5.20.1. SUPAPolicyAccessMetadataDef Attributes ............. 94 5.20.1.1. The Attribute "supaPolAccessPrivilegeDef" ..... 94 5.20.1.2. The Attribute "supaPolAccessPrivilegeModelName" 95 5.20.1.3. The Attribute "supaPolAccessPrivilegeModelRef" 95 Strassner, et al. Expires November 30, 2017 [Page 6]
Internet-Draft SUPA Generic Policy Model May 2017 Table of Contents (continued) 5.21. The Concrete Class "SUPAPolicyVersionMetadataDef" ....... 96 5.21.1. SUPAPolicyVersionMetadataDef Attributes ............ 96 5.21.1.1. The Attribute "supaVersionMajor" .............. 97 5.21.1.2. The Attribute "supaVersionMinor" .............. 98 5.21.1.3. The Attribute "supaVersionPatch" .............. 98 5.21.1.4. The Attribute "supaVersionPreRelease" ......... 98 5.21.1.5. The Attribute "supaVersionBuildMetadata" ...... 98 6. SUPA ECAPolicyRule Information Model .......................... 99 6.1. Overview ................................................. 99 6.2. Constructing a SUPAECAPolicyRule ........................ 101 6.3. Working With SUPAECAPolicyRules ......................... 101 6.4. The Abstract Class "SUPAECAPolicyRule" .................. 103 6.4.1. SUPAECAPolicyRule Attributes ....................... 105 6.4.1.1. The Attribute "supaECAPolicyRulePriority" ..... 105 6.4.1.2. The Attribute "supaECAPolicyRuleStatus" ....... 105 6.4.2. SUPAECAPolicyRule Relationships .................... 105 6.5. The Concrete Class "SUPAECAPolicyRuleAtomic" ............ 105 6.5.1. SUPAECAPolicyRuleAtomic Attributes ................. 106 6.5.1.1. The Attribute "supaECAPolActionEvalStrategy" .. 106 6.5.2. SUPAECAPolicyRuleAtomic Relationships .............. 107 6.6. The Concrete Class "SUPAECAPolicyRuleComposite" ......... 107 6.6.1. SUPAECAPolicyRuleComposite Attributes .............. 108 6.6.1.1. The Attribute "supaECAEvalRuleStrategy" ....... 108 6.6.2. SUPAECAPolicyRuleComposite Relationships ........... 110 6.6.2.1. The Aggregation "SUPAHasECAPolicyRule" ........ 110 6.6.2.2. The Association Class "SUPAHasECAPolicyRuleDetail" .................. 109 6.6.2.2.1. The Attribute "supaECAPolicyIsDefault" ... 109 6.7. The Abstract Class "SUPABooleanClause" .................. 109 6.7.1. SUPABooleanClause Attributes ....................... 110 6.7.1.1. The Attribute "supaBoolClauseBindValue" ....... 110 6.7.1.2. The Attribute "supaBoolClauseIsCNF" ........... 110 6.7.1.3. The Attribute "supaBoolClauseIsNegated" ....... 111 6.7.2. SUPABooleanClause Relationships .................... 111 6.8. The Concrete Class "SUPABooleanClauseAtomic" ............ 111 6.8.1. SUPABooleanClauseAtomic Attributes ................. 111 6.8.2. SUPABooleanClauseAtomic Relationships .............. 111 6.9. The Concrete Class "SUPABooleanClauseComposite" ......... 111 6.9.1. SUPABooleanClauseComposite Attributes .............. 112 6.9.2. SUPABooleanClauseComposite Relationships ........... 112 6.9.2.1. The Aggregation "SUPAHasBooleanClause" ........ 112 6.9.2.2. The Association Class "SUPAHasBooleanClauseDetail" .................. 112 6.9.2.2.1. The Attribute "supaIsHornClause" ............ 112 6.10. The Abstract Class "SUPAECAComponent" .................. 113 6.10.1. SUPAECAComponent Attributes ....................... 113 6.10.1.1. The Attribute "supaECACompIsTerm" ............ 113 6.10.2. SUPAECAComponent Relationships .................... 113 Strassner, et al. Expires November 30, 2017 [Page 7]
Internet-Draft SUPA Generic Policy Model May 2017 Table of Contents (continued) 6.11. The Concrete Class "SUPAPolicyEvent" ................... 114 6.11.1. SUPAPolicyEvent Attributes ........................ 114 6.11.1.1. The Attribute "supaPolicyEventData[1..n]" .... 114 6.11.1.2. The Attribute "supaPolicyEventEncoding[1..n]" 115 6.11.1.3. The Attribute "supaPolicyEventIsPreProcessed" 115 6.11.1.4. The Attribute "supaPolicyEventIsSynthetic" ... 115 6.11.1.5. The Attribute "supaPolicyEventTopic[0..n]" ... 116 6.11.2. SUPAPolicyEvent Relationships ..................... 116 6.12. The Concrete Class "SUPAPolicyCondition" ............... 116 6.12.1. SUPAPolicyCondition Attributes .................... 116 6.12.1.1. The Attribute "supaPolicyConditionData[1..n]" 116 6.12.1.2. The Attribute "supaPolicyConditionEncoding" .. 117 6.12.2. SUPAPolicyCondition Relationships ................. 117 6.13. The Concrete Class "SUPAPolicyAction" .................. 117 6.13.1. Restrictions about SUPAPolicyActions Calling SUPAPolicies ...................................... 118 6.13.2. SUPAPolicyAction Attributes ....................... 119 6.13.2.1. The Attribute "supaPolicyActionData[1..n]" ... 119 6.13.2.2. The Attribute "supaPolicyActionEncoding" ..... 119 6.13.3. SUPAPolicyAction Relationships .................... 120 7. Examples ..................................................... 121 7.1. Example 1: Blocking SNMP Traffic ....................... 121 7.1.1. Introduction ....................................... 121 7.1.2. Solution Approach .................................. 121 7.1.3. Solution for Case 1 (SUPAPolicies Control Behavior) ....................................... 122 7.1.3.1. Strategy ................................... 123 7.1.3.2. Implementation ............................. 124 7.1.4. Solution for Case 2 (SUPAPolicies Do Not Control Behavior) .................................. 127 7.1.4.1. Approach ...................................... 127 7.1.4.2. Implementation ............................. 128 8. Security Considerations ..................................... 130 9. IANA Considerations .......................................... 130 10. Contributors ................................................ 130 11. Acknowledgments ............................................. 130 12. References .................................................. 130 12.1. Normative References ................................... 130 12.2. Informative References ................................ 131 Authors' Addresses ............................................... 133 Appendix A. Brief Analyses of Previous Policy Work .............. 134 Strassner, et al. Expires November 30, 2017 [Page 8]
Internet-Draft SUPA Generic Policy Model May 2017 1. Overview This document defines an information model for representing policies using a common extensible framework that is independent of language, protocol, repository, and the level of abstraction of the content and meaning of a policy. This enables a common set of concepts defined in this information model to be mapped into different representations of policy (e.g., procedural, imperative, and declarative). It also enables different data models that use different languages, protocols, and repositories to optimize their usage. The definition of common policy concepts also provides better interoperability by ensuring that each data model can share a set of common concepts, independent of its level of detail or the language, protocol, and/or repository that it is using. It is also independent of the target data model that will be generated. This version of the information model focuses on defining one type of policy rule: the event-condition-action (ECA) policy rule. Accordingly, this document defines two sets of model elements: 1. A framework for defining the concept of policy, independent of how policy is represented or used; this is called the SUPA Generic Policy Information Model (GPIM) 2. A framework for defining a policy model that uses the event-condition-action (ECA) paradigm; this is called the SUPA ECA Policy Rule Information Model (EPRIM), and extends concepts from the GPIM. The combination of the GPIM and the EPRIM provides an extensible framework for defining policy that uses an event-condition-action representation that is independent of data repository, data definition language, query language, implementation language, and protocol. The Appendix provides a brief analysis of previous work in the field of policy modeling. 1.1. Introduction Simplified Use of Policy Abstractions (SUPA) defines a technology- independent neutral information model for creating high-level, possibly network-wide policies as input and producing element configurations (either whole or snippets) as output. SUPA addresses the needs of operators, end-users, and application developers to represent multiple types of ECA policy rules, such as for traffic selection and configuration or security. These ECA policy rules may vary in the level of abstraction to suit the needs of different actors (e.g., end-users vs. administrators) [1], [10]. Strassner, et al. Expires November 30, 2017 [Page 9]
Internet-Draft SUPA Generic Policy Model May 2017 Different constituencies of users would like to use terminology and concepts that are familiar to each constituency. Rather than require multiple software systems to be used for each constituency, a common information model enables these different concepts and terms to be mapped to elements in the information model. This facilitiates the use of a single software system to generate data models for each language. In the example shown in Figure 1 (which is a simplified Policy Continuum [10]), each constituency uses different concepts and terms (according to their skill sets and roles) to formulate (ECA) policy rules that are useful for their job functions. A unified information model is one way to build a consensual lexicon that enables terms from one language to be mapped to terms of another language. This approach enables the syntax of each language to be modified appropriate to its user while keeping a common set of semantics for all languages. This is shown in Figure 1. +-------------------+ | Information Model | | and one or more +<------------------------+ | Data Models | | +-------------------+ | | +---------------------+ | +---------------+ \| High-level Policies | \+-------------+ | | Business User |----| Without Technical |----| Language #1 +<----+ +---------------+ /| Terminology | /+-------------+ | +---------------------+ | | +---------------------+ | +---------------+ \| Policies That Use | \+-------------+ | | Developer |----| Classes, Attributes,|----| Language #2 +<----+ +---------------+ /| Relationships, ... | /+-------------+ | +---------------------+ | | ... ... ... | | +---------------------+ | +---------------+ \| Low-level Policies | \+-------------+ | | Admin |----| with Technology- |----| Language #n +<----+ +---------------+ /| Specific Terms in a | /+-------------+ | Specific Language | +---------------------+ Figure 1. Different Constituencies Need Different Policies More importantly, an information model defines concepts in a uniform way, enabling formal mapping processes to be developed to translate the information model to a set of data models. This simplifies the process of constructing software to automate the policy management process. It also simplifies the language generation process, though that is beyond the scope of this document. Strassner, et al. Expires November 30, 2017 [Page 10]
Internet-Draft SUPA Generic Policy Model May 2017 This common framework takes the form of an information model that is divided into one high-level module and one or more number of lower-level modules. A lower-level module extends the higher-level module into a new domain; each lower-level domain module can itself be extended to model more granular domain-specific (but still technology- and vendor-independent) concepts as necessary. Conceptually, a set of model elements (e.g., classes, attributes, constraints, and relationships) are used to define the Generic Policy Information Model (GPIM); this module defines a common set of policy concepts that are independent of the type of policy (e.g., imperative, procedural, declarative, or otherwise). Then, any number of additional modules can be derived from the GPIM; each additional module MUST extend the GPIM to define a new type of policy rule by adding to the GPIM. Each additoinal module MUST NOT alter any of the model elements of the GPIM. The use of extensions preserves the interoperability of this approach; if the base GPIM was modified, then this would adversely compromise interoperability. The SUPA ECA Policy Rule Information Model (EPRIM) extends the GPIM to represent policy rules that use the Event-Condition-Action (ECA) paradigm. 1.2. Changes Since Version -02 There are several changes in this version of this document compared to the previous versions of this document. They are: 1) Fixed ASCII art in several figures 2) Added enumerations to supaPolOpType to sync with I2NSF 3) Fixed supaVendorDecoratedCompEncoding 4) Corrected attribute definitions in supaPolicyCollection 5) Corrected attribute definition of supaPolMetadataIDEncoding 6) Added Figures 2 and 3; renumbered subsequent Figures 7) Enhanced supaPolicyEventEncoding definition 8) Added supaECAPolActionEcalStrategy to SUPAPolicyRuleComposite 9) Added section 6.13.1. 10) Added new section about design patterns (4.2.1) 11) Added new section describing how association classes are used (4.2.2) 12) ECA stuff 13) revised decorator pattern 14) Fixed typos 2. Conventions Used in This Document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. In this document, these words will appear with that interpretation only when in ALL CAPS. Lower case uses of these words are not to be interpreted as carrying [RFC2119] significance. Strassner, et al. Expires November 30, 2017 [Page 11]
Internet-Draft SUPA Generic Policy Model May 2017 3. Terminology This section defines acronyms, terms, and symbology used in the rest of this document. 3.1. Acronyms CLI Command Line Interface CRUD Create, Read, Update, Delete CNF Conjunctive Normal Form DNF Disjunctive Normal Form ECA Event-Condition-Action EPRIM (SUPA) ECA Policy Rule Information Model GPIM (SUPA) Generic Policy Information Model OAM&P Operations, Administration, Management, and Provisioning OID Object IDentifier SAT Satisfiability, short for Boolean Satisfiability Problem SUPA Simplified Use of Policy Abstractions TMF TeleManagent Forum (TM Forum) UML Unified Modeling Language URI Uniform Resource Identifier YANG A data definition language for use with NETCONF ZOOM Zero-touch Orchestration, Operations, and Management (a TMF project that also works on information models) 3.2. Definitions This section defines the terminology that is used in this document. 3.2.1. Core Terminology The following subsections define the terms "information model" and "data model", as well as "container" and "policy container". 3.2.1.1. Information Model An information model is a representation of concepts of interest to an environment in a form that is independent of data repository, data definition language, query language, implementation language, and protocol. Note: this definition is more specific than that of [RFC3198], so as to focus on the properties of information models. That definition was: "An abstraction and representation of the entities in a managed environment, their properties, attributes and operations, and the way that they relate to each other. It is independent of any specific repository, software usage, protocol, or platform." Strassner, et al. Expires November 30, 2017 [Page 12]
Internet-Draft SUPA Generic Policy Model May 2017 3.2.1.2. Data Model A data model is a representation of concepts of interest to an environment in a form that is dependent on data repository, data definition language, query language, implementation language, and/or protocol (typically, but not necessarily, all five). Note: this definition is more specific than that of [RFC3198], so as to focus on the properties of data models that are generated from information models. That definition was: "A mapping of the contents of an information model into a form that is specific to a particular type of data store or repository." 3.2.1.3. Class A class is a set of objects that exhibit a common set of characteristics and behavior. 3.2.1.3.1. Abstract Class An abstract class is a class that cannot be directly instantiated. It MAY have abstract or concrete subclasses. It is denoted with a capital A (for abstract) near the top-left side of the class. 3.2.1.3.2. Concrete Class A concrete class is a class that can be directly instantiated. Note that classes are either abstract or concrete. In addition, once a class has been defined as concrete in the hierarchy, all of its subclasses MUST also be concrete. It is denoted with a capital C (for concrete) near the top-left side of the class. 3.2.1.4. Container A container is an object whose instances may contain zero or more additional objects, including container objects. A container provides storage, query, and retrieval of its contained objects in a well-known, organized way. 3.2.1.5. PolicyContainer In this document, a PolicyContainer is a special type of container that provides at least the following three functions: 1. It uses metadata to define how its content is interpreted 2. It separates the content of the policy from the representation of the policy 3. It provides a convenient control point for OAM&P operations The combination of these three functions enables a PolicyContainer to define the behavior of how its constituent components will be accessed, queried, stored, retrieved, and how they operate. Strassner, et al. Expires November 30, 2017 [Page 13]
Internet-Draft SUPA Generic Policy Model May 2017 This document does NOT define a specific data type to implement a PolicyContainer, as many different types of data types can be used. However, the data type chosen SHOULD NOT allow duplicate members in the PolicyContainer. In addition, order is irrelevant, since priority will override any initial order of the members of this PolicyContainer. 3.2.2. Policy Terminology The following terms define different policy concepts used in the SUPA Generic Policy Information Model (GPIM). Note that the prefix "SUPA" is used for all classes and relationships defined in this model to ensure name uniqueness. Similarly, the prefix "supa" is defined for all SUPA class attributes. 3.2.2.1. SUPAPolicyObject A SUPAPolicyObject is the root of the GPIM class hierarchy. It is an abstract class that all classes inherit from, except the SUPAPolicyMetadata class and its subclasses. 3.2.2.2. SUPAPolicy A SUPAPolicy is, in this version of this document, an ECA policy rule that is a type of PolicyContainer. The PolicyContainer MUST contain a SUPAECAPolicyRule, SHOULD contain one or more SUPAPolicyMetadata objects, and MAY contain other elements that define the semantics of the policy rule. Policies are generically defined as a means to monitor and control the changing and/or maintaining of the state of one or more managed objects [1]. In this context, "manage" means that one or more of the following six fundamental operations are supported: create, read, write, delete, start, and stop) [16]. 3.2.2.3. SUPAPolicyClause A SUPAPolicyClause is an abstract class. Its subclasses define different types of clauses that are used to create the content for different types of SUPAPolicies. For example, the SUPABooleanClause subclass models the content of a SUPAPolicy as a Boolean clause, where each Boolean clause is made up of a set of reusable objects. In contrast, a SUPAEncodedClause encodes the entire clause as a set of attributes. All types of SUPAPolicies MUST use one or more SUPAPolicyClauses to construct a SUPAPolicy. Strassner, et al. Expires November 30, 2017 [Page 14]
Internet-Draft SUPA Generic Policy Model May 2017 3.2.2.4. SUPAECAPolicyRule An Event-Condition-Action (ECA) Policy (SUPAECAPolicyRule) is an abstract class that is a type of PolicyContainer. It represents a policy rule as a three-tuple, consisting of an event, a condition, and an action clause. In an information model, this takes the form of three different aggregations, one for each clause. Each clause MUST be represented by at least one SUPAPolicyClause. Optionally, the SUPAECAPolicyRule MAY contain zero or more SUPAPolicySources, zero or more SUPAPolicyTargets, and zero or more SUPAPolicyMetadata objects. Note that for this version of this document, ECA Policy Rules are the **only** types of Policies that are defined. 3.2.2.5. SUPAMetadata Metadata is, literally, data about data. SUPAMetadata is an abstract class that contains prescriptive and/or descriptive information about the object(s) to which it is attached. While metadata can be attached to any information model element, this document only considers metadata attached to classes and relationships. When defined in an information model, each instance of the SUPAMetadata class MUST have its own aggregation relationship with the set of objects that it applies to. However, a data model MAY map these definitions to a more efficient form (e.g., flattening the object instances into a single object instance). 3.2.2.6. SUPAPolicyTarget SUPAPolicyTarget is an abstract class that defines a set of managed objects that may be affected by the actions of a SUPAPolicyClause. A SUPAPolicyTarget may use one or more mechanisms to identify the set of managed objects that it affects; examples include OIDs and URIs. When defined in an information model, each instance of the SUPAPolicyTarget class MUST have its own aggregation relationship with each SUPAPolicy that uses it. However, a data model MAY map these definitions to a more efficient form (e.g., flattening the SUPAPolicyTarget, SUPAMetadata, and SUPAPolicy object instances into a single object instance). 3.2.2.7. SUPAPolicySource SUPAPolicySource is an abstract class that defines a set of managed objects that authored this SUPAPolicyClause. This is required for auditability and authorization policies, as well as some forms of deontic and alethic logic. Strassner, et al. Expires November 30, 2017 [Page 15]
Internet-Draft SUPA Generic Policy Model May 2017 A SUPAPolicySource may use one or more mechanisms to identify the set of managed objects that authored it; examples include OIDs and URIs. Specifically, policy CRUD MUST be subject to authentication and authorization, and MUST be auditable. Note that the mechanisms for doing these three operations are currently not included, and are for further discussion. When defined in an information model, each instance of the SUPAPolicySource class MUST have its own aggregation relationship with each SUPAPolicy that uses it. However, a data model MAY map these definitions to a more efficient form (e.g., flattening the SUPAPolicySource, SUPAMetadata, and SUPAPolicy object instances into a single object instance). 3.2.3. Modeling Terminology The following terms define different types of relationships used in the information models of the SUPA Generic Policy Information Model (GPIM). 3.2.3.1. Inheritance Inheritance makes an entity at a lower level of abstraction (e.g., the subclass) a type of an entity at a higher level of abstraction (e.g., the superclass). Any attributes and relationships that are defined for the superclass are also defined for the subclass. However, a subclass does NOT change the characteristics or behavior of the attributes or relationships of the superclass that it inherits from. Formally, this is called the Liskov Substitution Principle [7]. This principle is one of the key characteristics that is NOT followed in [4], [6], [RFC3060], and [RFC3460]. A subclass MAY add new attributes and relationships that refine the characteristics and/or behavior of it compared to its superclass. A subclass MUST NOT change inherited attributes or relationships. 3.2.3.2. Relationship A relationship is a generic term that represents how a first set of entities interact with a second set of entities. A recursive relationship sets the first and second entity to the same entity. There are three basic types of relationships, as defined in the subsections below: associations, aggregations, and compositions. A subclass MUST NOT change the multiplicity (see section 3.2.3.7) of a relationship that it inherits. A subclass MUST NOT change any attributes of a relation that it inherits that is realized using an association class (see section 3.2.3.6). Strassner, et al. Expires November 30, 2017 [Page 16]
Internet-Draft SUPA Generic Policy Model May 2017 3.2.3.3. Association An association represents a generic dependency between a first and a second set of entities. In an information model, an association MAY be represented as a class. 3.2.3.4. Aggregation An aggregation is a stronger type (i.e., more restricted semantically) of association, and represents a whole-part dependency between a first and a second set of entities. Three objects are defined by an aggregation: the first entity, the second entity, and a new third entity that represents the combination of the first and second entities. The entity owning the aggregation is referred to as the "aggregate", and the entity that is aggregated is referred to as the "part". In an information model, an aggregation MAY be represented as a class. 3.2.3.5. Composition A composition is a stronger type (i.e., more restricted semantically) of aggregation, and represents a whole-part dependency with two important behaviors. First, an instance of the part is included in at most one instance of the aggregate at a time. Second, any action performed on the composite entity (i.e., the aggregate) is propagated to its constituent part objects. For example, if the composite entity is deleted, then all of its constituent part entities are also deleted. This is not true of aggregations or associations - in both, only the entity being deleted is actually removed, and the other entities are unaffected. In an information model, a composition MAY be represented as a class. 3.2.3.6. Association Class A relationship may be implemented as an association class. This is used to define the relationship as having its own set of features. (Note: in this document, all relationships are implemented as association classes for consistency and to simplify implementation.) More specifically, if the relationship is implemented as an association class, then the attributes of the association class, as well as other relationships that the association class participates in, may be used to define the semantics of the relationship. If the relationship is not implemented as an association class, then no additional semantics (beyond those defined by the type of the relationship) are expressed by the relationship. Strassner, et al. Expires November 30, 2017 [Page 17]
Internet-Draft SUPA Generic Policy Model May 2017 3.2.3.7. Multiplicity A specification of the range of allowable cardinalities that a set of entities may assume. This is always a pair of ranges, such as 1 - 1 or 0..n - 2..5. 3.2.3.8. Navigability A relationship may restrict one object from accessing the other object. This document defines two choices: 1. Each object is navigable by the other, which is indicated by NOT providing any additional symbology, or 2. An object A can navigate to object B, but object B cannot navigate to object A. This is indicated by an open-headed arrow pointing to the object that cannot navigate to the other object. An example is shown below: +---------+ 3..4 +---------+ | | 1..2 \| | | Class A |--------------| Class B | | | /| | +---------+ +---------+ The above figure shows a navigability restriction. Class A can navigate to Class B, but Class B cannot navigate to Class A. This is a mandatory association, since none of the multiplicities contain a '0'. This association reads as follows: Class A depends on 3 to 4 instances of Class B, and Class B depends on 1 to 2 instances of Class A. 3.3. Symbology The following symbology is used in this document. 3.3.1. Inheritance Inheritance: a subclass inherits the attributes and relationships of its superclass, as shown below: +------------+ | Superclass | +------+-----+ / \ I I I +------+-----+ | Subclass | +------------+ Strassner, et al. Expires November 30, 2017 [Page 18]
Internet-Draft SUPA Generic Policy Model May 2017 3.3.2. Association Association: Class B depends on Class A, as shown below: +---------+ +---------+ +---------+ +---------+ | | \| | | Class A |------| Class B | | Class A |------| Class B | +---------+ +---------+ | | /| | +---------+ +---------+ association with no association with navigability restrictions navigability restrictions 3.3.3. Aggregation Aggregation: Class B is the part, Class A is the aggregate, as shown below: +---------+ +---------+ +---------+ | |/ \ +---------+ | |/ \ \| | | Class A | A ---| Class B | | Class A | A ------| Class B | | |\ / +---------+ | |\ / /| | +---------+ +---------+ +---------+ aggregation with no aggregation with navigability restrictions navigability restrictions 3.3.4. Composition Composition: Class B is the part, Class A is the composite, as shown below: +---------+ +---------+ +---------+ | |/ \ +---------+ | |/ \ \| | | Class A | C ---| Class B | | Class A | C ------| Class B | | |\ / +---------+ | |\ / /| | +---------+ +---------+ +---------+ composition with no composition with navigability restrictions navigability restrictions 3.3.5. Association Class Association Class: Class C is the association class implementing the relationship D between classes A and B Strassner, et al. Expires November 30, 2017 [Page 19]
Internet-Draft SUPA Generic Policy Model May 2017 +---------+ +---------+ | Class A |----+-----| Class B | +---------+ ^ +---------+ | | +----------+----------+ | Association Class C | +---------------------+ 3.3.6. Abstract vs. Concrete Classes In UML, abstract classes are denoted with their name in italics. For this draft, a capital 'A' will be placed at either the top left or right corner of the class to signify that the class is abstract. Similarly, a captial 'C' will be placed in the same location to represent a concrete class. This is shown below. A C +---------+ +---------+ | Class A | | Class B | +---------+ +---------+ An Abstract Class A Concrete Class Strassner, et al. Expires November 30, 2017 [Page 20]
Internet-Draft SUPA Generic Policy Model May 2017 4. Policy Abstraction Architecture This section describes the policy abstractions that are used in SUPA. The following abstractions are provided: o The GPIM defines a technology-neutral information model that can express the concept of Policy. o All classes, except for SUPAPolicyMetadata, inherit from SUPAPolicyObject, or one of its subclasses. o SUPAPolicyObject and SUPAPolicyMetadata are designed to inherit from classes in another model; the GPIM does not define an "all-encompassing" model. o This version of this document restricts the expression of Policy to a set of event-condition-action clauses. o Each clause is defined as a Boolean expression, and MAY also be defined as a reusable object. o Clauses may be combined to form more complex Boolean expressions. o The purpose of the GPIM is to enable different policies that have fundamentally different representations to share common model elements. Policy statements, which are implemented as instances of the SUPAPolicyClause class, separate the content of a Policy from its representation. This is supported by: o All policy rules (of which SUPAECAPolicyRule is the first example of a concrete class) are derived from the SUPAPolicyStructure class. o All objects that are components of policy rules are derived from the SUPAPolicyComponentStructure class. o A SUPAPolicy MUST contain at least one SUPAPolicyClause. o A SUPAPolicy MAY specify one or more SUPAPolicyTarget, SUPAPolicySource, and SUPAPolicyMetadata objects to augment the semantics of the SUPAPolicy o A SUPAPolicyClause has two subclasses: o A SUPABooleanClause, which is used to build SUPAECAPolicyRules from reusable objects. o A SUPAEncodedClause, which is used for using attributes instead of objects to construct a SUPAECAPolicyRule. o A SUPAECAPolicyRule defines the set of events and conditions that are responsible for executing its actions; it MUST have at least one event clause, at least one condition clause, and at least one action clause. o The action(s) of a SUPAECAPolicyRule are ONLY executed if both the event and condition clauses evaluate to TRUE o A SUPAPolicyAction MAY invoke another SUPAPolicyAction in another SUPAECAPolicyRule (see section 6.13). o SUPAMetadata MAY be defined for any SUPAPolicyObject class. o SUPAMetadata MAY be prescriptive and/or descriptive in nature. This model, and its abstractions, define an interoperable representation of policies that can be communicated between different actors. Generation and execution of these policies is beyond the scope of this document. Strassner, et al. Expires November 30, 2017 [Page 21]
Internet-Draft SUPA Generic Policy Model May 2017 4.1. Motivation The power of policy management is its applicability to many different types of systems. There are many different actors that can use a policy management system, including end-users, operators, application developers, and administrators. Each of these constituencies have different concepts and skills, and use different terminology. For example, an operator may want to express an operational rule that states that only Platinum and Gold users can use streaming multimedia applications. As a second example, a network administrator may want to define a more concrete policy rule that looks at the number of dropped packets and, if that number exceeds a programmable threshold, changes the queuing and dropping algorithms used. SUPA may be used to define other types of policies, such as for systems and operations management; an example is: "All routers and switches must have password login disabled". See section 3 of [8] for additional declarative and ECA policy examples. All of the above examples are commonly referred to as "policy rules", but they take very different forms, since they are at very different levels of abstraction and typically authored by different actors. The first was very abstract, and did not contain any technology-specific terms, while the second was more concrete, and likely used technical terms of a general (e.g., IP address range, port numbers) as well as a vendor-specific nature (e.g., specific queuing, dropping, and/or scheduling algorithms implemented in a particular device). The third restricted the type of login that was permissible for certain types of devices in the environment. Note that the first two policy rules could directly affect each other. For example, Gold and Platinum users might need different device configurations to give the proper QoS markings to their streaming multimedia traffic. This is very difficult to do if a common policy model does not exist, especially if the two policies are authored by different actors that use different terminology and have different skill sets. More importantly, the users of these two policies likely have different job responsibilities. They may have no idea of the concepts used in each policy. Yet, their policies need to interact in order for the business to provide the desired service. This again underscores the need for a common policy framework. Certain types of policy rules (e.g., ECA) may express actions, or other types of operations, that contradict each other. SUPA provides a rich object model that can be used to support language definitions that can find and resolve such problems. Models built using this IM are intended primarily for communicating policy, not for executing policy. Strassner, et al. Expires November 30, 2017 [Page 22]
Internet-Draft SUPA Generic Policy Model May 2017 4.2. SUPA Approach The purpose of the SUPA Generic Policy Information Model (GPIM) is to define a common framework for expressing policies at different levels of abstraction. SUPA uses the GPIM as a common vocabulary for representing policy concepts that are independent of language, protocol, repository, and level of abstraction. This enables different actors to author and use policies at different levels of abstraction. This forms a policy continuum [1] [2], where more abstract policies can be translated into more concrete policies, and vice-versa. Most systems define the notion of a policy as a single entity. This assumes that all users of policy have the same terminology, and use policy at the same level of abstraction. This is rarely, if ever, true in modern systems. The policy continuum defines a set of views (much like RM-ODP's viewpoints [9]) that are each optimized for an actor playing a specific role. SUPA defines the GPIM as a standard vocabulary and set of concepts that enable different actors to use different formulations of policy. This corresponds to the different levels in the policy continuum, and as such, can make use of previous experience in this area. It may be necessary to translate a Policy from a general to a more specific form (while keeping the abstraction level the same). For example, the declarative policy "Every network attached to a VM must be a private network owned by someone in the same group as the owner of the VM" may be translated to a more formal form (e.g., into Datalog, as in OpenStack Congress). It may also be necessary to translate a Policy to a different level of abstraction. For example, the previous Policy may need to be translated to a form that network devices can process directly. This requires a common framework for expressing policies that is independent of the level of abstraction that a Policy uses. 4.2.1. Design Patterns A design pattern defines a reusable solution to a commonly occuring software design problem. It is not a finished solution, because of its generic nature. Rather, it is a "template" that outlines how to solve a problem that occurs in many different situations. In order to provide internal and external consistency, the SUPA Information Model uses several design patterns in key places withinhe the model. The following sub-sections describe three of the design patterns that this model uses. Strassner, et al. Expires November 30, 2017 [Page 23]
Internet-Draft SUPA Generic Policy Model May 2017 4.2.1.1. Composite Pattern One common issue is that some classes may need to be able to contain other classes. A common analogy is a folder system - folders can contain folders and files, but (typically) files do not contain folders. This is addressed by the Composite Pattern. The Composite Pattern creates a minimum of two subclasses, one for representing objects that can stand alone (e.g., files), and one for representing objects that serve as collections (e.g., folders). An example of this is SUPAECAPolicyRule. The composite subclass (e.g., SUPAECAPolicyRuleComposite) has an aggregating association back to or from the parent class (e.g., SUPAECAPolcyRule). This allows one to have composite entities which are made up of either other composites, or any of the atomic subclasses (e.g., SUPAECAPolicyRuleAtomic). While some models use recursive associations for this, experience has shown that this causes inappropriate associations, such as leading to an atomic subclass being able to contain more complex instances of the parent class. 4.2.1.2. Decorator Pattern Another common issue is the need to have a highly extensible set of additional information that MAY need to be added for certain object instances. Some of this can be done with metadata, but often, the information to be added forms a part of the object instance behavior. This is addressed by the decorator pattern [11]. A good example is SUPAPolicyClause, whose definition and behavior can be extended dynamically at runtime by wrapping its object instance with other objects. This is explained below. An aggregation is defined between SUPAPolicyClause and the superclass of the set of classes that form the Decorator Pattern (i.e., SUPAPolicyClauseComponentDecorator). This aggregation enables zero or more concrete subclasses of the SUPAPolicyClauseComponentDecorator class to "wrap" (i.e., be attached to) the instance of the class being decorated (i.e., SUPAPolicyClause in this example). This has the effect of creating a new object that appears to be a SUPAPolicyClause, but contains new attributes and behavior that are added to the existing attributes and behavior of the SUPAPolicyClause. Clients that are using the decorated object (i.e., SUPAPolicyClause) are **not** aware of these changes. The SUPAPolicyClauseComponentDecorator class has a number of specific subclases that each represent additional kinds of information that can be attached to a SUPAPolicyClause object instance. In this example, concrete subclasses of SUPAPolicyTerm and SUPAECAComponent, along with SUPAPolicyCollection and other Strassner, et al. Expires November 30, 2017 [Page 24]
Internet-Draft SUPA Generic Policy Model May 2017 subclasses, define optional information that can be attached to a SUPAPolicyClause. More specifically, each concrete subclass of the SUPAPolicyClause class can be decorated by each concrete subclass of the SUPAPolicyClauseComponentDecorator class. This means that the SUPAPolicyClauseComponentDecorator object has an instance variable that holds a reference to a SUPAPolicyClause object. Since the SUPAPolicyClauseComponentDecorator object has the same interface as the SUPAPolicyClause object, the SUPAPolicyClauseComponentDecorator class (and all of its subclasses) are transparent to clients of the SUPAPolicyClause class (and its subclasses). Hence, all SUPAPolicyClauseComponentDecorator object instances can add attributes and/or methods to the concrete instance of the chosen subclass of SUPAPolicyClause. Figure 2 shows how this is done for methods. - Figure 2a shows the initial object to be wrapped - Figure 2b shows the SUPAPolicyEvent object wrapping the SUPAEncodedClause object - Figure 2c shows SUPAGenericDecoratedComponent object wrapping the SUPAPolicyEvent object. +-------------------+ | SUPAEncodedClause | | eval() | ===> +-------------------+ (a) Initial Object +------------------------+ | SUPAPolicyEvent | | eval() | | +-------------------+ | | | SUPAEncodedClause | | ===> | | eval() | | | +-------------------+ | +------------------------+ (b) SUPAPolicyEvent "wraps" SUPAEncodedClause +--------------------------------+ | SUPAGenericDecoratedComponent | | eval() | | +-----------------------+ | | | SUPAPolicyEvent | | | | eval() | | | | +-------------------+ | | | | | SUPAEncodedClause | | | | | | eval() | | | | | +-------------------+ | | | +-----------------------+ | +--------------------------------+ (c) SUPAGenericDecoratedComponent "wraps" SUPAPolicyEvent Figure 2. Conceptual Depiction of eval() Decorated Method Strassner, et al. Expires November 30, 2017 [Page 25]
Internet-Draft SUPA Generic Policy Model May 2017 When the eval() method is called in the outermost object (SUPAGenericDecoratedComponent), it delegates to the eval() method of SUPAPolicyEvent, which in turn delegates to the eval() method of SUPAEncodedClause. This method executes and returns the results to SUPAPolicyEvent, which executes and returns the results to SUPAGenericDecoratedComponent, which executes and returns the final result. In addition, decorators may be applied to decorators. This is accomplished by using a concrete subclass of the decorating classes (SUPAPolicyComponentDecorator), which then decorates a concrete subclass of the parent decorator (i.e., SUPAPolicyClauseComponentDecorator). This enables the basic information to have either individual decorations or complex decorator aggregates. 4.2.2. Association Classes An association class enables attributes, operations, and other features to be added to an association. Consider the following example. An Employee can work for a Company, in which case the Company pays the Employee a salary. Now, where do you define the salary attribute? If you define the salary as part of the Company, then every Employee gets the same salary. If you define salary as an attribute of Employee, then that Employee gets the same salary for all Companies that the Employee works for. These problems result from the fact that different Employees can work for the same Company, and an Employee may also work for different Companies. Hence, the salary paid to the Employee is in reality a function of the relationship between Employee and Company, since the salary changes when the Employee works for a different Company. This is shown in Figure 3. C C +----------+ 1..n 0..n +---------+ | | IsEmployedBy | | | Employee +--------+-------+ Company | | | ^ | | +----------+ | +---------+ | C | +--------+-----------+ | IsEmployedByDetail | | | | salary : Float | | | +--------------------+ Figure 3. Using Association Classes Strassner, et al. Expires November 30, 2017 [Page 26]
Internet-Draft SUPA Generic Policy Model May 2017 Figure 3 shows that a class, named IsEmployedByDetail, is used to represent the semantics of the IsEmployedBy association. Note that an association class can define its own (i.e., class- level) attributes, methods, and relationships; all of these can be used to define the intended semantics of the association class. Note: class-level attributes, methods, and relationships are often called **static** attributes, methods, and relationships. Examples include: o restrict when the relationship can be established and/or terminated o restrict which classes of one end of the relationship can be associated with which classes from the other end of the relationship o define attributes that depend on both classes in the relationship In the above example, the use of a class enables the attributes of the association class (i.e., IsEmployedByDetail) to be used to define the salary attribute. This is because the salary attribute is a function of both the particular Employee being paid the salary and the Company that the Employee works for. In this example, we have chosen to give the salary attribute a datatype of type Float. Optionally, the association class can be subclassed to refine additional behavior. In addition, the association class can have its own set of relationships; these relationships could be used make the attributes of the association class dependent on other classes. 4.3. SUPA Generic Policy Information Model Overview Figure 5 illustrates the approach for representing policy rules in SUPA. The top two layers are defined in this document; the bottom layer (Data Models) are defined in separate documents. Conceptually, the GPIM defines a set of objects that define the key elements of a Policy independent of how it is represented or its content. As will be shown, there is a significant difference between SUPAECAPolicyRules (see Section 6) and other types of policies (see Section 7). In principle, other types of SUPAPolicies could be defined, but the current charter is restricted to using only event-condition-action SUPAPolicies as exemplars. Note: the GPIM MAY be used without the EPRIM. However, in order to use the EPRIM, the GPIM MUST also be used. Strassner, et al. Expires November 30, 2017 [Page 27]
Internet-Draft SUPA Generic Policy Model May 2017 +----------------------------------------------+ | SUPA Generic Policy Information Model (GPIM) | +----------------------+-----------------------+ / \ | | +-----------------+--------------+ | | | | +-----------+---------------+ +-------------+-------------+ | SUPAECAPolicyRule | | Other Policy Models that | | Information Model (EPRIM) | | are Derived from the GPIM | +-----------+---------------+ +-------------+-------------+ / \ / \ | | | | +-----------+-----------+ +-----------+------------+ | ECAPolicyRule | | Other Types of | | Data Model | | Data Models | +-----------------------+ +------------------------+ Figure 5. Overview of SUPA Policy Rule Abstractions This draft defines the GPIM and EPRIM. This draft further assumes that the SUPA Information Model is made up of either the GPIM or the combination of the GPIM and the EPRIM. Extensions to both the GPIM and the EPRIM can be made as long as these extensions do not conflict with the content and structure defined in the GPIM and EPRIM. If the GPIM and EPRIM are part of another information model, then they should collectively still define a single information model. The GPIM defines the following concepts: o A class defining the top of the GPIM class hierarchy, called SUPAPolicyObject o Four subclasses of SUPAPolicyObject, representing: o the top of the Policy hierarchy, called SUPAPolicyStructure o the top of the Policy component hierarchy, called SUPAPolicyComponentStructure o PolicySource o PolicyTarget The SUPAPolicyStructure class is the superclass for all types of Policies (e.g., imperative, declarative, and others). This document is currently limited to imperative (e.g., ECA) policies. However, care has been taken to ensure that the attributes and relationships of the SUPAPolicyStructure class are extensible, and can be used for more types of policies than just ECA policies. This yields the following high-level structure: Strassner, et al. Expires November 30, 2017 [Page 28]
Internet-Draft SUPA Generic Policy Model May 2017 A +------------------+ | SUPAPolicyObject | +--------+---------+ / \ I I +----------------+--------------------+ I I I A I I A I +--------+------------+ I +------------+-----------------+ | SUPAPolicyStructure | I | SUPAPolicyComponentStructure | +----+----------------+ I +------------+-----------------+ / \ I / \ I +--------+----+ I I I I I I C I I I I +-------+----------+ I I I | SUPAPolicySource | I I I +------------------+ I I I I I I +-------------+ I I I +-----+-------+ I C I I I I +-------+----------+ A I I I | SUPAPolicyTarget | +--------+---------+ I I +------------------+ | SUPAPolicyClause | I A I +------------------+ I +-----+------------+ I | SUPAECAPolicyRule| A I +------------------+ +--------------------------+---------+ | SUPAPolicyClauseComponentDecorator | +------------------------------------+ Figure 6. Functional View of the Top-Level GPIM Note that all classes except the SUPAPolicySource and the SUPAPolicyTarget classes are defined as abstract. This provides more freedom for the data modeler in implementing the data model. For example, if the data model uses an object-oriented language, such as Java, then the above structure enables all of the abstract classes to be collapsed into a single concrete class. If this is done, attributes as well as relationships are inherited. 4.3.1. SUPAPolicyObject A SUPAPolicyObject serves as a single root of the SUPA system (i.e., all other classes in the model are subclasses of the SUPAPolicyObject class) except for the Metadata objects, which are in a separate class hierarchy. This simplifies code generation and reusability. It also enables SUPAPolicyMetadata objects to be attached to any appropriate subclass of SUPAPolicyObject. Strassner, et al. Expires November 30, 2017 [Page 29]
Internet-Draft SUPA Generic Policy Model May 2017 4.3.2. SUPAPolicyStructure SUPAPolicyStructure is an abstract superclass that is the base class for defining different types of policies (however, in this version of this document, only ECA policy rules are modeled). It serves as a convenient aggregation point to define atomic (i.e., individual policies that can be used independently) and composite (i.e., hierarchies of policies) SUPAPolicies; it also enables PolicySources and/or PolicyTargets to be associated with a given set of Policies. SUPAPolicies are defined as either a stand-alone PolicyContainer or a hierarchy of PolicyContainers. A PolicyContainer specifies the structure, content, and optionally, source, target, and metadata information for a SUPAPolicy. This is implemented by the subclasses of SUPAPolicyStructure. For example, the composite pattern is used to create two subclasses of the SUPAECAPolicyRule class; SUPAECAPolicyRuleAtomic is used for stand-alone policies, and SUPAECAPolicyRuleComposite is used to build hierarchies of policies. This document defines a SUPAPolicy as an ECA Policy Rule, though the GPIM enables other types of policies to be defined and used with an ECA policy rule. The GPIM model is used in [2] and [5], along with extensions that allow [2] and [5] to define multiple types of policies that are derived from the GPIM. They also allow different combinations of different types of policy rules to be used with each other. Most previous work cannot define different types of policy rules; please see Appendix A for a comparison to previous work. 4.3.3. SUPAPolicyComponentStructure SUPAPolicyComponentStructure is an abstract superclass that is the base class for defining components of different types of policies. SUPAPolicyStructure subclasses define the structure of a policy, while SUPAPolicyComponentStructure subclasses define the content that is contained in the structure of a policy. For example, a SUPAECAPolicyRule is an imperative policy rule, and defines its structure; its event, condition, and action clauses are populated by SUPAPolicyComponentStructure subclasses. The strength of this design is that different types of policies (e.g., imperative and declarative policies) can be represented using a common set of policy components. Please see the Appendix for a comparison to previous work. Strassner, et al. Expires November 30, 2017 [Page 30]
Internet-Draft SUPA Generic Policy Model May 2017 4.3.4. SUPAPolicyClause All policies derived from the GPIM are made up of one or more SUPAPolicyClauses, which define the content of the Policy. This enables a Policy of one type (e.g., ECA) to invoke Policies of the same or different types. SUPAPolicyClause is an abstract class, and serves as a convenient aggregation point for assembling other objects that make up a SUPAPolicyClause. The GPIM defines a single concrete subclass of SUPAPolicyClause, called SUPAEncodedClause. This is a generic clause, and can be used by any type of Policy in a stand-alone fashion. It can also be used in conjunction with other SUPAPolicyClauses. The EPRIM also defines a subclass of SUPAPolicyClause; see section 6.7). The structure of the GPIM is meant to provide an extensible framework for defining different types of policies. This is demonstrated by the EPRIM (see section 6) and the LSIM (see the Appendices) that each define new subclasses of SUPAPolicyClause (i.e., SUPABooleanClause and SUPALogicClause, respectively) without defining new classes that have no GPIM superclass. A SUPAPolicyClause is defined as an object. Therefore, clauses and sets of clauses are objects, which promotes reusability. 4.3.5. SUPAPolicyClauseComponentDecorator One of the problems in building a policy model is the tendency to have a multitude of classes, and hence object instances, to represent different combinations of policy events, conditions, and actions. This can lead to class and/or relationship explosion. Please see Appendix A for a comparison to previous work. SUPAPolicyClauses are constructed using the Decorator Pattern [11]. This is a design pattern that enables behavior to be selectively added to an individual object, either statically or dynamically, without affecting the behavior of other objects from the same class. The decorator pattern uses composition, instead of inheritance, to avoid class and relationship explosion. The decorator pattern also enable new objects to be composed from parts or all of existing objects without affecting the existing objects. This enables the resulting SUPAPolicyClause to be constructed completely from objects in the SUPA information model. This facilitates the construction of policies at runtime by a machine. This is also true of [2] and [5]; however, this is NOT true of most other models. Please see Appendix A for a comparison to previous work. Strassner, et al. Expires November 30, 2017 [Page 31]
Internet-Draft SUPA Generic Policy Model May 2017 SUPAPolicyClauseComponentDecorator is the superclass for 4 classes in the GPIM, and one additional class in the EPRIM, that can be used to form a SUPAPolicyClause. Each of these five classes may be used with all other classes, if desired. These classes are: o SUPAPolicyTerm, which enables a clause to be defined in a canonical {variable, operator, value} form o SUPAGenericDecoratedComponent, which enabled a custom object to be defined and then used in a SUPAPolicyClause o SUPAPolicyCollection, which enables a collection of objects to be gathered together and associated with all or a portion of a SUPAPolicyClause o SUPAPolicyComponentDecorator, which enables additional Decorators to wrap the SUPAPolicyClauseComponentDecorator o SUPAECAComponent, which defines Events, Conditions, and Actions as reusable objects This approach facilitates the machine-driven construction of policies. Note that this is completely optional; policies do not have to use these constructs. 4.3.6. SUPAPolicyTarget A SUPAPolicyTarget is a set of managed entities that a SUPAPolicy is applied to. A set includes individual and group membership. Data models implementations are free to populate the set using any appropriate mechanisms, such as reference by a property such as one or more roles, explicit lists, predicate expressions, or others. Note that the decision to define a managed entity as a SUPAPolicyTarget belongs with the management system; this model simply represents the fact that a given managed entity is defined as a SUPAPolicyTarget. Furthermore, the policy-based management system SHOULD ensure that the management entity performing the management operations has the proper permissions to perform the requested management operations. The design of the SUPAPolicyTarget addresses both of these criteria. 4.3.7. SUPAPolicySource A SUPAPolicySource is a set of managed entities that authored, or are otherwise responsible for, this SUPAPolicy. Note that a SUPAPolicySource does NOT evaluate or execute SUPAPolicies. Its primary use is for auditability and the implementation of deontic and/or alethic logic. 4.4. The Design of the GPIM The GPIM defines a policy as a type of PolicyContainer. For this version, only ECA Policy Rules will be described. However, it should be noted that the mechanism described is applicable to other types of policies (e.g., declarative) as well. Strassner, et al. Expires November 30, 2017 [Page 32]
Internet-Draft SUPA Generic Policy Model May 2017 4.4.1. Structure of Policies Recall that a PolicyContainer was defined as a special type of container that provides at least the following three functions: 1. It uses metadata to define how its content is described and/or prescribed 2. It separates the content of the policy from the representation of the policy 3. It provides a convenient control point for OAMP operations. The first requirement is provided by the ability for any subclass of Policy (the root of the information model) to aggregate one or more concrete instances of a SUPAPolicyMetadata class. This is explained in detail in section 5.2.2. The second requirement is met by representing an ECA Policy as having two parts: (1) a rule part and (2) components that make up the rule. Since functional and declarative policies are not, strictly speaking, "rules", the former is named PolicyStructure, while the latter is named PolicyComponentStructure. The third requirement is met by the concrete subclasses of PolicyStructure. Since they are PolicyContainers, they are made up of the SUPAECAPolicyRule, its commponents, and any metadata that applies to the PolicyContainer, the SUPAECAPolicyRule, and.or any components of the SUPAECAPolicyRule. This provides optional low-level control over any part of the SUPAECAPolicyRule. The above requirements result in the design shown in Figure 7. A SUPAHasPolicyMetadata A +------------------+/ \ \+--------------------+ | SUPAPolicyObject + A -----------------------+ SUPAPolicyMetadata | +---------+--------+\ / /+--------------------+ / \ 0..n 0..n I I +------+------------------------------------+ I I A I A I +--------+------------+ +------------------+-----------+ | SUPAPolicyStructure | | SUPAPolicyComponentStructure | +--------+------------+ +-------------+----------------+ / \ / \ I I I I (subclasses representing (subclasses representing different types of policies) different policy components) Figure 7. Structure of a Policy Strassner, et al. Expires November 30, 2017 [Page 33]
Internet-Draft SUPA Generic Policy Model May 2017 Note that aggregation in Figure 7 (named SUPAHasPolicyMetadata) is realized as an association class, in order to manage which set of Metadata can be aggregated by which SUPAPolicyObject. The combination of these three functions enables a PolicyContainer to define the behavior of how its constituent components will be accessed, queried, stored, retrieved, and how they operate. It is often necessary to construct groups of policies. The GPIM follows [2] and [5], and uses the composite pattern [11] to implement this functionality, as shown in Figure 8 below. There are a number of advantages to using the composite pattern over a simple relationship, as detailed in [11]. Figure 8 shows that SUPAPolicyStructure has a single subclass, called SUPAECAPolicyRule. Note, however, that other types of policies, such as declarative policies, can be defined as subclasses of SUPAPolicyStructure in the future. A +---------------------+ | SUPAPolicyStructure | +--------+------------+ / \ I I +---------------+----------------+ I I C I A I +----------------+---------------+ +-----------+-----------+ | Future Subclasses to Represent | | SUPAECAPolicyRule | | Represent Different Policies | +-----------------------+ +--------------------------------+ Figure 8. The Composite Pattern Applied to SUPAPolicyStructure 4.4.2. Representing an ECA Policy Rule An ECA policy rule is a 3-tuple, which is made up of an event clause, a condition clause, and an action clause. Each of these three types of clauses may in turn be made up of a Boolean combination of clauses of that type. Each clause may be viewed as a predicate, as it provides a TRUE or FALSE output. The canonical form of a clause is a 3-tuple of the form "variable operator value", and can be made into more complex Boolean expressions. For example, the SUPAPolicyClause: "((A AND B) OR NOT (C AND D)) consists of two clauses, "(A AND B)" and "(C OR D)", that are combined together using the operators OR and NOT. A SUPAECAPolicyRule is defined (in the EPRIM) as an abstract subclass of SUPAPolicyStructure. Strassner, et al. Expires November 30, 2017 [Page 34]
Internet-Draft SUPA Generic Policy Model May 2017 Note that the aggregation SUPAHasPolicyClause in Figure 9 is realized as an association class, in order to manage which set of SUPAPolicyClauses can be aggregated by which set of SUPAECAPolicyRules. This aggregation is defined at the SUPAPolicyStructure level, and not at the lower level of SUPAECAPolicyRule, so that non-ECA policies can also use this aggregation. A A +---------------------------+ +------------------+ | SUPAPolicyStructure | | SUPAPolicyClause | +---------+---------+-------+ +----------+-------+ / \ / \ 0..1 1..n / \ I A | I \ / | I | | I | SUPAHasPolicyClause | I +---------------+----------+ A I I +--------+----------+ A I | SUPAECAPolicyRule | +--------+------------------+ +-------------------+ | SUPAHasPolicyClauseDetail | +---------------------------+ Figure 9. SUPAECAPolicyRule Aggregating SUPAPolicyClauses Since a SUPAECAPolicyRule consists of three SUPAPolicyClauses, at least three separate instances of the SUPAHasPolicyClause aggregation are instantiated in order to make a complete SUPAECAPolicyRule, as shown in Figure 10. A A +-------------------+ +--------------------+ | SUPAECAPolicyRule | | SUPAPolicyClause | +--+----+----+------+ +-------+----+----+--+ / \ / \ / \ 0..1 1..n / \ / \ / \ A A A | | | \ / \ / \ / | | | | | | | | | | | | SUPAHasPolicyClause #1 | | | | | +------------------------------+ | | | | | | | | SUPAHasPolicyClause #2 | | | +----------------------------------------+ | | | | SUPAHasPolicyClause #3 | +--------------------------------------------------+ note: all 3 aggregations have a multiplicity of 0..1 - 1..n Figure 10. Instantiating a SUPAECAPolicyRule, part 1 Strassner, et al. Expires November 30, 2017 [Page 35]
Internet-Draft SUPA Generic Policy Model May 2017 In figure 10, SUPAECAPolicyRule is shown as "owning" these three aggregations, since it inherits them from its superclass (SUPAPolicyStructure). The three aggregations represent the event, condition, and action clauses of a SUPAECAPolicyRule. Note that each of these clauses MAY consist of one or more SUPAPolicyClauses. Similarly, each SUPAPolicyClause MAY consist of one or more predicates. In this way, complex event, condition, and action clauses, which are combinations of Boolean expressions that form a logical predicate) are supported, without having to define additonal objects (as is done in previous work; please see Appendix A for a comparison to previous work. The multiplicity of the SUPAHasPolicyClause aggregation is 0..n on the aggregate side and 1..n on the part side. This means that a particular SUPAECAPolicyRule MUST aggregate at least one SUPAPolicyClause, and that a given SUPAPolicyClause MAY be aggregated by zero or more SUPAECAPolicyRule objects. This cardinality MAY be refined to 3..n for SUPAECAPolicyRules, since a SUPAECAPolicyRule MUST have at least three separate clauses. However, since a SUPAPolicyStructure is the owner of this aggregation (which is inherited by SUPAECAPolicyRule), the cardinality is defined to be 1..n on the part side because other types of Policies have different needs. The 0..n cardinality means that a SUPAPolicyClause may be aggregated by zero or more SUPAECAPolicyRules. The zero is provided so that SUPAPolicyClauses can be stored in (for example) a repository before the SUPAECAPolicyRule is created; the "or more" recognizes the fact that multiple SUPAECAPolicyRules could aggregate the same SUPAPolicyClause. In Figure 10, suppose that SUPAHasPolicyClause#1, #2, and #3 represent the aggregations for the event, condition, and action clauses, respectively. This means that each of these SUPAHasPolicyClause aggregations must explicitly identify the type of clause that it represents. In looking at Figure 10, there is no difference between any of the three aggregations, except for the type of clause that the aggregation represents (i.e., event, condition, or action clause). Therefore, three different aggregations, each with their own association class, is not needed. Instead, the GPIM defines a single aggregation (SUPAHasPolicyClause) that is realized using a (single) abstract association class (SUPAHasPolicyClauseDetail); this association class is then subclassed into three concrete subclasses, one each to represent the semantics for an event, condition, and action clause. Strassner, et al. Expires November 30, 2017 [Page 36]
Internet-Draft SUPA Generic Policy Model May 2017 The policy management system may use any number of different software mechanisms, such as introspection or reflection, to determine the nature of the aggregation (i.e., what object types are being aggregated) in order to select the appropriate subclass of SUPAHasPolicyClauseDetail. The three subclasses of SUPAHasPolicyClauseDetail are named SUPAHasPolicyEventDetail, SUPAHasPolicyConditionDetail, and SUPAHasPolicyActionDetail, respectively. While Event, Condition, and Action objects are typically used in ECA policy rules, the design in this document enables them to be used as policy components of other types of policies as well. This is shown in Figure 11. A A +-------------------+ +------------------+ | SUPAECAPolicyRule | | SUPAPolicyClause | +---------+---------+ +----------+-------+ / \ 1..n 0..n / \ A | \ / | | | | SUPAHasPolicyClause | +--------------+-----------------+ ^ | A | +--------------+------------+ | SUPAHasPolicyClauseDetail | +--------------+------------+ / \ I I +----------------+-----------------------+ I I I C I C I C I +--------+-----+ +-------+----------+ +---------+-----+ |Event subclass| |Condition subclass| |Action subclass| +--------------+ +------------------+ +---------------+ Figure 11. Instantiating a SUPAECAPolicyRule, part 2 4.4.3. Creating SUPA Policy Clauses There are two different types of Policy Components. They are a SUPAPolicyClause and a SUPAPolicyClauseComponentDecorator. The former is used to construct SUPAECAPolicyRules, while the latter is used to add behavior to a SUPAPolicyClause. This enables the structure and capabilities of the SUPAPolicyClause to be adjusted dynamically at runtime. This is shown in Figure 12. Strassner, et al. Expires November 30, 2017 [Page 37]
Internet-Draft SUPA Generic Policy Model May 2017 A +------------------------------+ | SUPAPolicyComponentStructure | +---------------+--------------+ / \ I I +---------------+--------------------+ | | A | A | +--------+---------+ +---------------+--------------------+ | | | | | SUPAPolicyClause | | SUPAPolicyClauseComponentDecorator | | | | | +------------------+ +---------------------------+--------+ / \ 0..n 0..n / \ A | \ / | | | | SUPAPolicyClauseHasDecorator | +--------------------------------------------------+ Figure 12. Decorating SUPAPolicyClauses Every SUPAPolicyClause can be made up of a variable number of SUPAPolicyClauseComponentDecorators, so the multiplicity of the SUPAPolicyClauseHasDecorator aggregation is 0..n - 0..n. This means that a SUPAPolicyClause may have zero or more decorating objects, and that a SUPAPolicyClauseComponentDecorator MAY be associated with zero or more SUPAPolicyClauses. Note that the "zero" part of this multiplicity enables SUPAPolicyClauseComponentDecorator objects to be stored in a PolicyRepository without having to be bound to ability particular SUPAPolicyClause. The use of the decorator pattern avoids problems encountered in earlier models, which resulted in a proliferation of classes and relationships. Instead of using inheritance to statically create new classes to represent new types of objects, the decorator pattern uses composition to dynamically combine attributes and behavior from existing objects into new objects. This is done by defining an interface in SUPAPolicyComponent that all of the subclasses of SUPAPolicyComponent conform to. Since the subclasses are of the same type as SUPAPolicyComponent, they all have the same interface. This allows each concrete SUPAPolicyClauseComponentDecorator subclass to add its attributes and/or behavior to the concrete subclass of SUPAPolicyClause that it is decorating (or "wrapping"). This represents an important design optimization for data models. Note that a single SUPAECAPolicyRule can consist of any number of SUPAPolicyClauses, each of very different types. If inheritance was used, then a subclass AND an aggregation would be required for each separate clause that makes up the policy rule. Strassner, et al. Expires November 30, 2017 [Page 38]
Internet-Draft SUPA Generic Policy Model May 2017 Suppose composite objects are desired (e.g., a new object Foo is made up of existing objects Bar and Baz). If all that was needed was one attribute of Bar and two of Baz, the developer would still have to use the entire Bar and Baz classes. This is wasteful and inefficient. In contrast, the decorator pattern enables all, or just some, of the attributes and/or behavior of a class to "wrap" another class. This is used heavily in many production systems (e.g., the java.io package) because the result is only the behavior that is required, and no other objects are affected. SUPAPolicyClauseComponentDecorator is the superclass of five subclasses, as shown in Figure 13. A +------------------------------------+ | SUPAPolicyClauseComponentDecorator | +-----------------+------------------+ / \ I I I +------------+-+-----------+------------------+ I I I I I A I I I C I I +--------+-------+ I I +---------+------------+ I | SUPAPolicyTerm | I I | SUPAPolicyCollection | I +----------------+ I I +----------------------+ I (for defining I I (for defining sets and/or I clauses in a I I groups of objects) I canonical form) I I I I +---------------+ I C I I A I +----------------+--------------+ I +---------+--------+ | SUPAGenericDecoratedComponent | I | SUPAECAComponent | +-------------------------------+ I +------------------+ (for decorating concrete I (for defining reusable subclasses of SUPAPolicyClause) I event, condition, I and action objects) I A I +-------------+----------------+ | SUPAPolicyComponentDecorator | +------------------------------+ (for decorating SUPAPolicyClauseComponentDecorator objects with SUPAPolicyComponentDecorator objects) Figure 13. Subclasses of SUPAPolicyClauseComponentDecorator Strassner, et al. Expires November 30, 2017 [Page 39]
Internet-Draft SUPA Generic Policy Model May 2017 The SUPAPolicyClauseComponentDecorator class hierarchy is used to define classes that may be used to construct a SUPAPolicyClause. The decorator object can add behavior before, and/or after, it delegates to the object that it is decorating. The subclasses of SUPAPolicyClauseComponentDecorator provide a very flexible and completely dynamic mechanism to: 1) add or remove behavior to/from a SUPAPolicyClause object 2) ensure that objects are constructed using the minimum amount of features and functionality required If a SUPAEncodedClause is being used, then there is no need to use any of the SUPAPolicyClauseComponentDecorator subclasses, since the SUPAEncodedClause already completely defines the content of the SUPAPolicyClause. However, if a SUPAEncodedClause is NOT being used, then a SUPAPolicyClause SHOULD be constructed using one or more types of concrete subclasses of SUPAPolicyClauseComponentDecorator. These five subclasses provide five different ways to construct a SUPAPolicyClause: 1) SUPAPolicyTerm: as a {variable, operator, value} clause 2) SUPAGenericDecoratedComponent: as an encoded object (e.g., to pass YANG or CLI code) 3) SUPAPolicyCollection: as a collection of objects that requires further processing in order to be made into a SUPAPolicyClause 4) SUPAECAComponent: subclasses define reusable Event, Condition, or Action objects 5) SUPAPolicyComponentDecorator: as a new type of Decorator to augment any of the above four mechanisms These four different types of objects can be intermixed. For example, the first and fourth types can be combined as follows: Variable == Event.baz (A) Condition BETWEEN VALUE1 and VALUE2 (B) (Event.severity == 'Critical' AND (SLA.violation == TRUE OR User.class == 'Gold')) (C) In the above rules, (A) uses Event.baz to refer to an attribute of the Event class; (B) defines two different instances of a Value class, denoted as Value1 and Value2; (C) uses the nomenclature foo.bar, where foo is the name of a class, and bar is the name of an attribute of that class. Strassner, et al. Expires November 30, 2017 [Page 40]
Internet-Draft SUPA Generic Policy Model May 2017 4.4.4. Creating SUPAPolicyClauses The GPIM defines a single subclass of SUPAPolicyClause, called SUPAEncodedClause. This clause is generic in nature, and MAY be used with any type of policy (ECA or otherwise). The EPRIM defines an ECA-specific subclass of the GPIM, called a SUPABooleanClause, which is intended to be used with just ECA policy rules; however, other uses are also possible. Together, the GPIM and EPRIM provide several alternatives to implement a SUPAPolicyClause, enabling the developer to optimize the solution for different constraints: 1) The SUPAPolicyClause can be encoded using one or more SUPAEncodedClauses; a SUPAEncodedClause encodes the entire content of its respective event, condition, or action clause. 2) The SUPAPolicyClause can be defined using one or more SUPABooleanClauses; each of the three clauses can be defined as either a single SUPABooleanClause, or a combination of SUPABooleanClauses that are logically ANDed, ORed, and/or NOTed. 3) The above two mechanisms can be combined (e.g., the first used to define the event clause, and the second used to define the condition and action clauses). Figure 14 shows the subclasses of SUPAPolicyClause. A +------------------+ | SUPAPolicyClause | +--------+---------+ / \ I I I +---------------+-------------+ I I A I C I +--------+----------+ +----------+--------+ | SUPABooleanClause | | SUPAEncodedClause | +-------------------+ +-------------------+ Figure 14. Subclasses of SUPAPolicyClause SUPABooleanClause (see Section 6.7) is defined in the EPRIM, and is used to construct Boolean clauses that collectively make up a SUPAPolicyClause. It is abstract, so that the composite pattern can be applied to it, which enables hierarchies of Boolean clauses to be created. SUPAEncodedClause (see section 5.6) is used to encode the content of a SUPAPolicyClause as an attribute (instead of reusable objects). Strassner, et al. Expires November 30, 2017 [Page 41]
Internet-Draft SUPA Generic Policy Model May 2017 4.4.5. SUPAPolicySources A SUPAPolicySource is a set of managed entities that authored, or are otherwise responsible for, this SUPAPolicy. Note that a SUPAPolicySource does NOT evaluate or execute SUPAPolicies. Its primary use is for auditability, authorization policies, and other applications of deontic and/or alethic logic. The SUPAHasPolicySource aggregation defines the set of SUPAPolicySource objects that are sources for a given SUPAPolicy (as defined by a concrete subclass of SUPAPolicyStructure). Since SUPAECAPolicyRule is a subclass of SUPAPolicyStructure, it (and its subclasses) inherit this aggregation. This enables a set of SUPAPolicySource objects to be attached to a particular SUPAECAPolicyRule object. Figure 15 shows how SUPAPolicySources and SUPAPolicyTargets are attached to a SUPAPolicy. Note that both of these aggregations are defined as optional, since their multiplicity is 0..n - 0..n. In addition, both of these aggregations are realized as association classes, in order to be able to control which SUPAPolicySources and SUPAPolicyTargets are attached to a given SUPAECAPolicyRule. A +------------------+ | SUPAPolicyObject | +--------+---------+ / \ I I +--------------+-----+---------------------+ I I I A I C I C I +-----------+---------+ +-------+--------+ +--------+-------+ | SUPAPolicyStructure | |SUPAPolicySource| |SUPAPolicyTarget| +------+-------+------+ +----------+-----+ +----------+-----+ 0..n / \ / \ 0..n 0..n / \ 0..n / \ A A | | \ / \ / | | | | | | | | | | | +--------------------+ | | SUPAHasPolicySource | | | +-------------------------------------------------+ SUPAHasPolicyTarget Figure 15. ECAPolicyRules, SUPAPolicySources, and PolicyTargets Strassner, et al. Expires November 30, 2017 [Page 42]
Internet-Draft SUPA Generic Policy Model May 2017 A SUPAPolicySource MAY be mapped to a role (e.g., using the role-object pattern [11]); this indirection makes the system less fragile, as entities can be transparently added or removed from the role definition without adversely affecting the definition of the SUPAPolicy. Note that SUPAPolicyRole is a subclass of SUPAPolicyMetadata. 4.4.6. SUPAPolicyTargets A SUPAPolicyTarget defines the set of managed entities that a SUPAPolicy is applied to. This is useful for debugging, as well as when the nature of the application requires the set of managed entities affected by a Policy to be explicitly identified. This is determined by two conditions: 1) The set of managed entities that are to be affected by the SUPAPolicy must all agree to play the role of a SUPAPolicyTarget. For example, a managed entity may not be in a state that enables SUPAPolicies to be applied to it; hence, in this case, it MUST NOT assume the role of a SUPAPolicyTarget 2) A SUPAPolicyTarget must be able to: a) process (either directly or with the aid of a proxy) SUPAPolicies, or b) receive the results of a processed SUPAPolicy and apply those results to itself. Figure 15 showed how SUPAPolicyTargets are attached to SUPAECAPolicyRules. The SUPAHasPolicyTarget aggregation defines the set of SUPAPolicyTarget objects that are targets for (e.g., will be acted on) by a given SUPAPolicy (as defined by a concrete subclass of SUPAPolicyStructure). Since SUPAECAPolicyRule is a subclass of SUPAPolicyStructure, it (and its subclasses) inherit this aggregation. This enables a set of SUPAPolicyTarget objects to be attached to a particular SUPAECAPolicyRule object. A SUPAPolicyTarget MAY be mapped to a role (e.g., using the role-object pattern [11]); this indirection makes the system less fragile, as entities can be transparently added or removed from the role definition without adversely affecting the definition of the SUPAPolicy. Note that SUPAPolicyRole is a subclass of SUPAPolicyMetadata. 4.4.7. Policy Metadata Metadata is, literally, data about data. As such, it can be descriptive or prescriptive in nature. Strassner, et al. Expires November 30, 2017 [Page 43]
Internet-Draft SUPA Generic Policy Model May 2017 4.4.7.1. Motivation There is a tendency in class design to make certain attributes, such as description, status, validFor, and so forth, bound to a specific class (e.g., [6]). This is bad practice in an information model. For example, different classes in different parts of the class hierarchy could require the use of any of these attributes; if one class is not a subclass of the other, then they must each define the same attribute as part of their class structure. This makes it difficult to find all instances of the attribute and ensure that they are synchronized. Furthermore, context can dynamically change the status of an object, so an easy way to update the status of one object instance without affecting other instances of the same object is required. Many models, such as [4] and [6], take a simplistic approach of defining a common attribute high in the hierarchy, and making it optional. This violates classification theory, and defeats the purpose of an information model, which is to specify the differences in characteristics and behavior between classes (as well as define how different classes are related to each other). Note that this also violates a number of well-known software architecture principles, including: o the Liskov Substitution Principle [13] (if A is a subclass of B, then objects instantiated from class B may be replaced with objects instantiated from class A WITHOUT ALTERING ANY OF THE PROGRAM SEMANTICS) o the Single Responsibility Principle [14] (every class should have responsibility over one, and only one, part of the functionality provided by the program) o the Open/Closed Principle (software should be open for extension, but closed for modification) [17] o the Interface-Segreation Principle (clients should not be forced to depend on methods that they do not use) [14] o the Dependency Inversion Principle (high-level modules should not depend on low-level modules; both should depend on abstractions) [14] Most models use inheritance, not composition. The former is simpler, but has some well-known problems. One is called "weak encapsulaton", meaning that a subclass can use attributes and methods of a superclass, but if the superclass changes, the subclass may break. Another is that each time a new object is required, a new subclass must be created. These problems are present in [RFC3460], [4], and [6]. Strassner, et al. Expires November 30, 2017 [Page 44]
Internet-Draft SUPA Generic Policy Model May 2017 Composition is an alternative that provides code that is easier to use. This means that composition can provide data models that are more resistant to change and easier to use. By using composition, we can select just the metadata objects that are needed, instead of having to rely on statically defined objects. We can even create new objects from a set of existing objects through composition. Finally, we can use the decorator pattern to select just the attributes and behaviors that are required for a given instance. In [2] and [5], a separate metadata class hierarchy is defined to address this problem. This document follows this approach. 4.4.7.2. Design Approach The goal of the GPIM is to enable metadata to be attached to any subclass of SUPAPolicyObject that requires it. Since this is a system intended for policy-based management, it therefore makes sense to be able to control which metadata is attached to which policies dynamically (i.e., at runtime). One solution is to use the Policy Pattern [1], [2], [6], [12]. This pattern was built to work with management systems whose actions were dependent upon context. The Policy Pattern is shown in Figure 16, and works as follows: Defines +----------+ Behavior +------------+ | Policies +----------------+ | SUPAPolicy | +----+-----+ 1..n | +------+-----+ 0..n / \ | / \ 0..n | | A | | \ / | 1..n \ / | | +-----------+--------------+ | | | SUPAPolicyMetadataDetail | | | +-----------+--------------+ | | | | | Selects | | | Policies | | | | | | +-------------------->+ | Applies | / \ Behavior | A | 0..n \ / \ / 0..n +----+-----+ +--------+---------+ | Context | |SUPAPolicyMetadata| +----------+ +------------------+ Figure 16. Context-Aware Policy Rules Strassner, et al. Expires November 30, 2017 [Page 45]
Internet-Draft SUPA Generic Policy Model May 2017 o Context is derived from all applicable system inputs (e.g., OAMP data from network elements, business goals, time of day, geo-location, etc.). o Context is then used to select a working set of Policies. o Policies are then used to define behavior at various control points in the system. o One simple type of control point is an association class. Since the association class represents the semantics of how two classes are related to each other, then o ECAPolicyRule actions can be used to change the attribute values, methods, and relationships of the association class o This has the affect of changing how the two classes are related to each other o Finally, as context changes, the working set of policies change, enabling the behavior to be adjusted to follow changes in context (according to appropriate business goals and other factors, of course) in a closed loop manner. 4.4.7.2.1. Policies and Actors The Policy Continuum ([1] [5] [10] [12]) was defined to associate different actors with different policies at different levels of business and/or technical specificity. Context-aware policy rules, and the Policy Pattern, were defined to realize this association. Four important functions related to the lifecycle of policies are design, implementation, deployment, and execution. There are many different possible definitions of these functions (even for policy lifecycle management); however, for the purposes of this document, they are defined as follows: o Design: The process of defining a software architecture to satisfy user requirements. o Development: the process of documenting, programming, testing, and maintaining code and applications as part of a software product o Deployment: the process that assembles and transfers completed software artifacts to a state that enables their execution o Execution: the process of installing, activating, running, and subsequently deactivating executable software products The design process is responsible for producing a software architecture. This emphasizes the design, as opposed to the programming, of software systems. In contrast to design, development emphasizes constructing software artifacts via coding and documentation. Strassner, et al. Expires November 30, 2017 [Page 46]
Internet-Draft SUPA Generic Policy Model May 2017 Deployment may be described as the process of releasing software. It includes all of the operations required to assemble a completed software product. It typically also includes the process of preparing a software product for execution (e.g., assembling a set of software products into a larger product, determining if the consumer site has appropriate resources to install and execute the software product, and collecting information on the feasibility of using the software product). This contrasts with the execution process, which is the set of processes that follow deployment. In summary, exemplar states in the policy lifecycle process include: o Design: determining how the policy-based management system will operate o Development: documenting, programming, testing, and maintaining policies and policy components o Deployment: assembling the components of a policy-based management system o Execution: installing, enabling, running, disabling, and uninstalling policies and policy components 4.4.7.2.2. Deployment vs. Execution of Policies One of the primary reasons for separating the deployment and execution processes is to differentiate between environments that are not ready to execute policies (i.e., deployment) and environments that are ready to execute policies (i.e., execution). This is an important consideration, since policies that are related to the same set of tasks may be deployed in many different places (e.g., in a policy system vs. in a network device). In addition, each managed entity in the set of SUPAPolicyTargets may or may not be in a state that allows SUPAPolicies to be applied to it (see section 4.4.6.). Hence, this design includes dedicated class attributes for getting and setting the deployment and execution status, as well as enabling and disabling, SUPAPolicies (see section 5.3.1.). 4.4.7.2.3. Using SUPAMetadata for Policy Deployment and Execution One way of encoding deployment and execution status for policies and policy components is to attach Metadata objects to affected SUPAPolicyStructure and SUPAPolicyComponentStructure objects. This provides an extensible and efficient means to describe and/or prescribe deployment and/or execution status of a policy or a policy component. It is extensible, since classes and relationships can be used, as opposed to a set of attributes. It is efficient, because the decorator pattern (see section 5.7) is used (this enables attributes and/or methods of objects, or the entire object, to be used to add characteristics and/or behavior to a given object. Strassner, et al. Expires November 30, 2017 [Page 47]
Internet-Draft SUPA Generic Policy Model May 2017 SUPAPolicyMetadata objects (see sections 5.16 - 5.20) may be attached to the SUPAECAPolicyRule and/or any of its components to define additional semantics of the SUPAECAPolicyRule. For example, SUPAAccessMetadataDef (see section 5.19) and/or SUPAVersionMetadataDef (see section 5.20) may be attached to define the access privileges and version information, respectively, of a policy rule and/or its components. The SUPAPolicyStructure defines an attribute, supaPolDeployStatus, (see section 5.3.1.3.) that SUPAPolicyMetadata objects can use to get and set the deployment and execution status of a SUPAPolicy. This allows metadata to be used to alter the deployment and/or execution state of a policy (or a set of policy components) without having to affect other parts of the policy-based management system. The supaPolDeployStatus attribute indicates that this SUPAPolicy can or cannot be deployed. If it cannot be deployed. The reverse is also true (and hence, forms a closed-loop system controlled by metadata). For example, if the set of deployed SUPAPolicies are SUPAECAPolicyRules, then when the actions of these SUPAECAPolicyRules are executed, the overall context has changed (see section 4.4.7.2). The context manager could then change attribute values (directly or indirectly) in the SUPAPolicyMetadataDetail association class. This class represents the behavior of the SUPAHasPolicyMetadata aggregation, which is used to define which SUPAPolicyMetadata can be attached to which SUPAPolicy objet in this particular context. For example, the access privileges of a policy and/or policy component could be changed dynamically, according to changes in context. By using the decorator pattern on SUPAPolicyMetadata, any number of SUPAPolicyMetadata objects (or their attributes, etc.) can be wrapped around a concrete subclass of SUPAPolicyMetadata. This is shown in Figure 17 below. 4.4.7.3. Structure of SUPAPolicyMetadata SUPAPolicyMetadata also uses the decorator pattern to provide an extensible framework for defining metadata to attach to SUPAPolicy subclasses. Its two principal subclasses are SUPAPolicyConcreteMetadata and SUPAPolicyMetadataDecorator. The former is used to define concrete subclasses of SUPAPolicyMetadata that are attached at runtime to SUPAPolicy subclasses, while the latter is used to define concrete objects that represent reusable attributes, methods, and relationships that can be added to subclasses of SUPAPolicyConcreteMetadata. Strassner, et al. Expires November 30, 2017 [Page 48]
Internet-Draft SUPA Generic Policy Model May 2017 For example, concepts like identification, access control, and version information are too complex to represent as a single attribute, or even a couple of attributes - they require the generic power of objects to represent their characteristics and behavior. Furthermore, defining concrete classes to represent these concepts in the policy hierarchy is fragile, because: 1. not all objects that use these concepts need all of the information represented by them (e.g., two subclasses of an Identification Object may be Passport and Certificate, but these two objects are rarely used together, and even those contexts that use one of these classes may not need all of the data in that class) 2. defining a class means defining its attributes, methods, and relationships at a particular place in the hierarchy; this means that defining a relationship between a class A and another class B SHOULD only be done if all of the subclasses of B can use the attributes, methods, and relationships of A (e.g., in the above example, defining a relationship between an Identification Object and a superclass of a router class is not appropriate, since routers do not use Passports) Therefore, an association class is used to define the semantics of the SUPAHasPolicyMetadata aggregation. This follows the strategy defined in Section 4.2.2. Figure 17 illustrates this approach. The SUPAHasPolicyMetadataDetail association class contains attributes that define which SUPAPolicyMetadata objects can be aggregated by which SUPAPolicyObjects. This also enables SUPAPolicies to be defined that get and set the values of these attributes. (Note that for this approach to work, the association class is defined as a concrete class.) The multiplicity of the SUPAHasPolicyMetadata aggregation is defined as 0..n - 0..n, which makes this approach optional. Since a class encapsulates attributes, methods, and behavior, defining the Identification Object in the above example as a type of SUPAPolicyMetadata object enables the decorator pattern to be used to attach all or part of that object to other objects that need it. Strassner, et al. Expires November 30, 2017 [Page 49]
Internet-Draft SUPA Generic Policy Model May 2017 A +------------------+ | SUPAPolicyObject | +--------+---------+ / \ 0..n A \ / | A | 0..n +--------------------+ | SUPAHasPolicyMetadata \| | +-------------+-----------------+ SUPAPolicyMetadata | ^ /| | | +------+------+------+ C | / \ | 1..n +-------------+---------------+ I | 0..n | | I | +----------+ SUPAHasPolicyMetadataDetail | I | | | | I | | +-----------------------------+ I | | I | | C I | | 0..n +----------------------------+ I | +----------+ SUPAPolicyConcreteMetadata +IIIIIIIII+ | +----------------------------+ I | I | A I | +-----------------------------+ I | | SUPAPolicyMetadataDecorator +IIIIIIIII+ | +-------+--------------+------+ | / \ / \ 0..1 | I A | I \ / | I | | subclasses for adding | | behavior to policies +-----------------------+ and policy components SUPAHasMetadataDecorator Figure 17. SUPAPolicyMetadata Association Class Relationships Figure 18 shows a relevant portion of the SUPAPolicyMetadata hierarchy. SUPAPolicyConcreteMetadata is a concrete class that subclasses of the SUPAPolicyMetadataDecorator class can wrap. Two such subclasses, SUPAPolicyAccessMetadataDef and SUPAPolicyVersionMetadataDef, are shown in Figure 18. This enables access control and version information to be added statically (at design time) or dynamically (at runtime) to SUPAPolicyConcreteMetadata; this enables metadata-driven systems to adjust the behavior of the management system to changes in context, business rules, services given to end-users, and other similar factors. This is discussed more in sections 5.18 - 5.20. Strassner, et al. Expires November 30, 2017 [Page 50]
Internet-Draft SUPA Generic Policy Model May 2017 A +--------------------+ | | SUPAHasMetadataDecorator | SUPAPolicyMetadata +-------------------+ | | 1..n | +---------+----------+ | I | I | I | +-------------+-----------------+ | | | | C | | / \ +---------+------------------+ | A | SUPAPolicyConcreteMetadata | A | 0..1 \ / +----------------------------+ +--------+------------+-------+ | SUPAPolicyMetadataDecorator | +------------+----------------+ I +------------------------------+--------+ I I I I C I C I +---------------+-------------+ +---------------------+--------+ | SUPAPolicyAccessMetadataDef | | SUPAPolicyVersionMetadataDef | +-----------------------------+ +------------------------------+ Figure 18. SUPAPolicyMetadata Subclasses and Relationships Strassner, et al. Expires November 30, 2017 [Page 51]
Internet-Draft SUPA Generic Policy Model May 2017 5. GPIM Model This section defines the classes, attributes, and relationships of the GPIM. 5.1. Overview The overall class hierarchy is shown in Figure 19. (Class of another model that SUPA is integrating into) | +---SUPAPolicyObject (Sec 5.2) | +---SUPAPolicyStructure (Sec 5.3) | +---SUPAPolicyComponentStructure (Sec 5.4) | | | +---SUPAPolicyClause (Sec 5.5) | | | | | +---SUPAEncodedClause (Sec 5.6) | | | +---SUPAPolicyClauseComponentDecorator (Sec 5.7) | | | +---SUPAPolicyTerm (Sec 5.8) | | | | | +---SUPAPolicyVariable (Sec 5.9) | | | | | +---SUPAPolicyOperator (Sec 5.10) | | | | | +---SUPAPolicyValue (Sec 5.11) | | | +---SUPAGenericDecoratedComponent (Sec 5.12) | | | +---SUPAPolicyCollection (Sec 5.13) | | | +---SUPAPolicyComponentDecorator (Sec 5.14) | +---SUPAPolicySource (Sec 5.15) | +---SUPAPolicyTarget (Sec 5.16) (Class of another model that SUPAPolicyMetadata is integrating into) | +---SUPAPolicyMetadata (Sec 5.17) | +---SUPAPolicyConcreteMetadata (Sec 5.18) | +---SUPAPolicyMetadataDecorator (Sec 5.19) | +---SUPAPolicyAccessMetadataDef (Sec 5.20) | +---SUPAPolicyVersionMetadataDef (5.20) Figure 19. Main Classes of the GPIM Strassner, et al. Expires November 30, 2017 [Page 52]
Internet-Draft SUPA Generic Policy Model May 2017 SUPAPolicy is the root of the SUPA class hierarchy. For implementations, it is assumed that SUPAPolicy is subclassed from a class from another model. Note that SUPAPolicyMetadata MAY be subclassed from the same or (preferably) a different class in the external model. Classes, attributes, and relationships that are marked as "mandatory" MUST be part of a conformant implementation (i.e., a schema MUST contain these entities). This does not mean that these entities must be instantiated; rather it means that they must be able to be instantiated. Classes, attributes, and relationships that are marked as "optional" MAY be part of a conformant implementation. Note that the Single Responsibility Principle [14] mandates that subclasses should not change inherited attributes. Unless otherwise stated, all classes (and attributes) defined in this section were abstracted from DEN-ng [2]. 5.2. The Abstract Class "SUPAPolicyObject" This is a mandatory abstract class. Figure 20 shows the SUPAPolicyObject class, and its four subclasses. A 0..n 0..n A +----------------+/ \ \+------------------+ |SUPAPolicyObject+ A --------------------------+SUPAPolicyMetadata| +--------+-------+\ / SUPAHasPolicyMetadata /+------------------+ / \ I I +-----------------+----------------+-----------+ I I I I A I I I I +--------+------------+ I I I | SUPAPolicyStructure | I I I +---------------------+ I I I A I I I +-----------------+------------+ I I | SUPAPolicyComponentStructure | I I +------------------------------+ I I C I I +---------+--------+ I | SUPAPolicyTarget | I +------------------+ I C I +----------+-------+ | SUPAPolicySource | +------------------+ Figure 20. SUPAPolicyObject and Its Subclasses Strassner, et al. Expires November 30, 2017 [Page 53]
Internet-Draft SUPA Generic Policy Model May 2017 This class is the root of the SUPA class hierarchy. It defines the common attributes and relationships that all SUPA subclasses inherit. A SUPAPolicyObject MAY be qualified by a set of zero or more SUPAPolicyMetadata objects. This is provided by the SUPAHasPolicyMetadata aggregation (see Section 5.2.2). This enables the semantics of the SUPAPolicyObject to be more completely specified. 5.2.1. SUPAPolicyObject Attributes This section defines the attributes of the SUPAPolicyObject class. These attributes are inherited by all subclasses of the GPIM except for the SUPAPolicyMetadata class, which is a sibling class. 5.2.1.1. Object Identifiers This document defines two class attributes in SUPAPolicyObject, called supaPolObjIDContent and supaPolObjIDEncoding, that together define a unique object ID. This enables all class instances to be uniquely identified. One of the goals of SUPA is to be able to generate different data models that support different types of protocols and repositories. This means that the notion of an object ID must be generic. It is inappropriate to use data modeling concepts, such as keys, Globally Unique IDentifiers (GUIDs), Universally Unique IDentifiers (UUIDs), Fully Qualified Domain Names (FQDNs), Fully Qualified Path Names (FQPNs), Uniform Resource Identifiers (URIs), and other similar mechanisms, to define the structure of an information model. Therefore, a synthetic object ID is defined using these two class attributes. This can be used to facilitate mapping to different data model object schemes. The two attributes work together, with the supaPolObjIDContent attribute defining the content of the object ID and the supaPolObjIDEncoding attribute defining how to interpret the content. These two attributes form a tuple, and together enable a machine to understand the syntax and value of an object identifier for the object instance of this class. Similarly, all SUPA classes are attributes are both uniquely named as well as prepended with the prefixes "SUPA" and "supa", respectively, to facilitate model integration. Strassner, et al. Expires November 30, 2017 [Page 54]
Internet-Draft SUPA Generic Policy Model May 2017 5.2.1.2. The Attribute "supaPolObjIDContent" This is a mandatory string attribute that represents part of the object identifier of an instance of this class. It defines the content of the object identifier. It works with another class attribute, called supaPolObjIDEncoding, which defines how to interpret this attribute. These two attributes form a tuple, and together enable a machine to understand the syntax and value of an object identifier for the object instance of this class. This is based on the DEN-ng class design [2]. 5.2.1.3. The Attribute "supaPolObjIDEncoding" This is a mandatory non-zero enumerated integer attribute that represents part of the object identifier of an instance of this class. It defines the format of the object identifier. It works with another class attribute, called supaPolObjIDContent, which defines the content of the object ID. These two attributes form a tuple, and together enable a machine to understand the syntax and value of an object identifier for the object instance of this class. The supaPolObjIDEncoding attribute is mapped to the following values: 0: error 1: init 2: primary_key 3: foreign_key 4: GUID 5: UUID 6: URI 7: FQDN 8: FQPN 9: string_instance_id The values 0 and 1 represent an error state and an initialization state, respectively. The value 9 defines the canonical representation, in ASCII, of an instance ID of this object. 5.2.1.4. The Attribute "supaPolicyDescription" This is an optional string attribute that defines a free-form textual description of this object. 5.2.1.5. The Attribute "supaPolicyName" This is an optional string attribute that defines the name of this Policy. This enables any existing generic naming attribute to be used for generic naming, while allowing this attribute to be used to name Policy entities in a common manner. Note that this is NOT the same as the commonName attribute of the Policy class defined in [RFC3060], as that attribute is intended to be used with just X.500 cn attributes. Strassner, et al. Expires November 30, 2017 [Page 55]
Internet-Draft SUPA Generic Policy Model May 2017 5.2.2. SUPAPolicyObject Relationships The SUPAPolicyObject class currently defines a single relationship, as defined in the subsection below. 5.2.2.1. The Aggregation "SUPAHasPolicyMetadata" This is a mandatory aggregation that defines the set of SUPAPolicyMetadata that are aggregated by this particular SUPAPolicyObject. This aggregation is defined in section 5.16.2. 5.2.2.2. The Association Class "SUPAHasPolicyMetadataDetail" This is a mandatory concrete association class that defines the semantics of the SUPAPolicyMetadata aggregation. This enables the attributes and relationships of the SUPAPolicyMetadataDetail class to be used to constrain which SUPAPolicyMetadata objects can be aggregated by this particular SUPAPolicyObject instance. This association class is defined in Section 5.16.2.2. 5.3. The Abstract Class "SUPAPolicyStructure" This is a mandatory abstract class that is used to represent the structure of a SUPAPolicy. This class (and all of its subclasses) is a type of PolicyContainer. SUPAPolicyStructure was abstracted from DEN-ng [2], and a version of this class is in the process of being added to [5]. However, the version in [5] differs significantly. First, the class and relationship definitions ared different. Second, [5] uses the composite pattern. Neither of these are implemented in this document because of optimizations done to the SUPA class hierarchy that are NOT present in [5]. For this release, the only official type of policy that is supported is the event-condition-action (ECA) type of policy rule. However, the structure of the SUPA hierarchy is defined to facilitate adding new types of rules later. A SUPAPolicy may take the form of an individual policy or a set of policies. This requirement is supported by applying the composite pattern to subclasses of the SUPAPolicyStructure class, as shown in Figure 8. In this document, this is done for the SUPAECAPolicyRule subclass, and results in two subclasses: SUPAECAPolicyRuleAtomic (for defining stand-alone policies) and SUPAECAPolicyRuleComposite (for defining hierarchies of policies). Note that there is no need for a "match strategy attribute" that some models [RFC3460], [4], [6] have; this is because the SUPAPolicyStructure class is used just for containment. Hence, the containers themselves serve as the scoping component for nested policies. Strassner, et al. Expires November 30, 2017 [Page 56]
Internet-Draft SUPA Generic Policy Model May 2017 5.3.1. SUPAPolicyStructure Attributes The following subsections define the attributes of the SUPAPolicyStructure class. The SUPAPolicyStructure class has a number of attributes that have no counterpart in the SUPAPolicyComponentStructure class. This is because these attributes are only appropriate at the level of a policy rule, not at the level of a policy component. Care must be taken in adding attributes to this class, because the behavior of future subclasses of this class (e.g., declarative and functional policies) is very different than the behavior of SUPAECAPolicyRules. 5.3.1.1. The Attribute "supaPolAdminStatus" This is an optional attribute, which is an enumerated non-negative integer. It defines the current administrative status of this SUPAPolicyClause. Values include: 0: error 1: init 2: enabled 3: disabled 4: in test (i.e., no operational traffic can be passed) The values 0 and 1 represent an error state and an initialization state, respectively. Values 2 and 3 mean that this SUPAPolicyStructure is administratively enabled or disabled, respectively. A value of 4 means that this SUPAPolicyStructure is currently in a special test mode and SHOULD NOT be used as part of an OAM&P policy. 5.3.1.2. The Attribute "supaPolContinuumLevel" This is an optional non-negative integer attribute. It defines the level of abstraction, or policy continuum level [10], of this particular SUPAPolicy. The value assignment of this class is dependent on the application; however, it is recommended that for consistency with other SUPA attributes, the values of 0 and 1 are reserved for error and initialization states. By convention, lower values represent more abstract levels of the policy continuum. For example, a value of 1 could represent business policy, a value of 2 could represent application-specific policies, and a value of 3 could represent low=level policies for network administrators. Strassner, et al. Expires November 30, 2017 [Page 57]
Internet-Draft SUPA Generic Policy Model May 2017 5.3.1.3. The Attribute "supaPolDeployStatus" This is an optional enumerated, non-negative integer attribute. The purpose of this attribute is to indicate that this SUPAPolicy can or cannot be deployed by the policy management system. This attribute enables the policy manager to know which SUPAPolicies to retrieve, and may be useful for the policy execution system for planning the staging of SUPAPolicies. Values include: 0: error 1: init 2: deployed and enabled 3: deployed and in test 4: deployed but not enabled 5: ready to be deployed 6: cannot be deployed The values 0 and 1 represent an error state and an initialization state, respectively. A value of 2 means that the policy management system MAY use this SUPAPolicy. A value of 3-5 means that the policy management system SHOULD NOT use this SUPAPolicy until it is put into an enabled state. 5.3.1.4. The Attribute "supaPolExecFailStrategy" This is an optional non-negative, enumerated integer that defines what actions, if any, should be taken by this SUPAPolicyStructure object if it fails to execute correctly. Note that some systems may not be able to support all options specified in this enumeration. If rollback is supported by the system, then option 2 may be skipped. Options 3 and 4 can be used by systems that do and do not support rollback. Values include: 0: error 1: init 2: attempt rollback of all actions taken and stop execution 3: attempt rollback of only the action that failed and stop execution 4: stop execution but do not rollback any actions 5: ignore failure and continue execution The values 0 and 1 represent an error state and an initialization state, respectively. A value of 2 means that ALL execution is stopped, rollback of all actions (whether successful or not) is attempted, and that SUPAPolicies that otherwise would have been executed are ignored. A value of 3 means that execution is stopped, and rollback is attempted for ONLY the SUPAPolicy that failed to execute correctly. A value of 4 means that execution is stopped, but no actions are rolled back. A value of 5 means that the failure is ignored, and execution continues. Strassner, et al. Expires November 30, 2017 [Page 58]
Internet-Draft SUPA Generic Policy Model May 2017 5.3.2. SUPAPolicyStructure Relationships The SUPAPolicyStructure class owns four relationships, which are defined in the following subsections. It also inherits the SUPAHasPolicyMetadata aggregation (see section 5.17.2.1.). 5.3.2.1. The Aggregation "SUPAHasPolicySource" This is an optional aggregation, and defines the set of SUPAPolicySource objects that are attached to this particular SUPAPolicyStructure object. The semantics of this aggregation are defined by the SUPAHasPolicySourceDetail association class. PolicySource objects are used for authorization policies, as well as to enforce deontic and alethic logic. The multiplicity of this aggregation is 0..n - 0..n. This means that it is an optional aggregation; zero or more SUPAPolicySource objects may be aggregated by this SUPAPolicyStructure object, and zero or more SUPAPolicyStructure objects may aggregate this particular SUPAPolicySource object. 5.3.2.2. The Association Class "SUPAHasPolicySourceDetail" This is an optional concrete association class, and defines the semantics of the SUPAHasPolicySource aggregation. The attributes and relationships of this class can be used to define which SUPAPolicySource objects can be attached to which particular set of SUPAPolicyStructure objects. 5.3.2.2.1. The Attribute "supaPolSrcIsAuthenticated" This is an optional Boolean attribute. If the value of this attribute is true, then this SUPAPolicySource object has been authenticated by this particular SUPAPolicyStructure object. 5.3.2.2.2. The Attribute "supaPolSrcIsTrusted" This is an optional Boolean attribute. If the value of this attribute is TRUE, then this particular SUPAPolicySource object has been verified to be trusted by this particular SUPAPolicyStructure object. 5.3.2.3. The Aggregation "SUPAHasPolicyTarget" This is an optional aggregation, and defines the set of SUPAPolicyTargets that are attached to this particular SUPAPolicyStructure. The semantics of this aggregation is defined by the SUPAHasPolicyTargetDetail association class. The purpose of this class is to explicitly identify managed objects that will be affected by the execution of one or more SUPAPolicies. Strassner, et al. Expires November 30, 2017 [Page 59]
Internet-Draft SUPA Generic Policy Model May 2017 The multiplicity of this aggregation is 0..n - 0..n. This means that it is an optional aggregation; zero or more SUPAPolicyTarget objects may be aggregated by this SUPAPolicyStructure object, and zero or more SUPAPolicyStructure objects may aggregate this particular SUPAPolicyTarget object. 5.3.2.4. The Association Class "SUPAHasPolicyTargetDetail" This is an optional concrete association class, and defines the semantics of the SUPAPolicyTargetOf aggregation. The attributes and relationships of this class can be used to define which SUPAPolicyTargets can be attached to which particular set of SUPAPolicyStructure objects. 5.3.2.4.1. The Attribute "supaPolTgtIsAuthenticated" This is an optional Boolean attribute. If the value of this attribute is true, then this SUPAPolicyTarget object has been authenticated by this particular SUPAPolicyStructure object. 5.3.2.4.2. The Attribute "supaPolTgtIsEnabled" This is an optional Boolean attribute. If its value is TRUE, then this SUPAPolicyTarget is able to be used as a SUPAPolicyTarget. This means that it meets two specific criteria: 1. it has agreed to play the role of a SUPAPolicyTarget (i.e., it is willing to have SUPAPolicies applied to it, and 2. it is able to either process (directly or with the aid of a proxy) SUPAPolicies or receive the results of a processed SUPAPolicy and apply those results to itself. 5.3.2.5. The Association "SUPAHasPolExecFailTakeAction" This is an optional association that defines which, if any, actions should be taken if this SUPAPolicyStructure object instance fails to execute correctly. The semantics of this association are defined in the SUPAHasPolExecFailTakeActionDetail association class. For a given SUPAPolicyStructure object A, this association defines a set of policy action objects B to execute if (and only if) the SUPAPolicyStructure object A failed to execute correctly. The multiplicity of this association is defined as 0..n on the owner (A) side and 1..n on the part (B) side. This means that this association is optional; if it is instantiated, then at least one SUPAPolicyStructure MUST be instantiated by this SUPAPolicyStructure object. Similarly, one or more SUPAPolicyStructure objects may be associated with this given SUPAPolicyStructure object. Strassner, et al. Expires November 30, 2017 [Page 60]
Internet-Draft SUPA Generic Policy Model May 2017 5.3.2.6. The Association Class "SUPAHasPolExecFailTakeActionDetail" This is an optional concrete class that defines the semantics for the SUPAHasPolExecFailTakeAction association. The attributes and/or relationships of this association class can be used to determine which policy action objects are executed in response to a failure of the SUPAPolicyStructure object instance that owns this association. The association defines the set of policy actions from one SUPAPolicyStructure object to be executed if another SUPAPolicyStructure object fails to execute properly. Figure 21 illustrates this approach. A +---------------------------+ 0..n | +---------------------------------+ | | SUPAHasPolExecFailTakeAction | | SUPAPolicyStructure |/ | | + --------------+-----------------+ | |\ ^ +---------------------------+ 1..n | | C | +------------------+-----------------+ | SUPAHasPolExecFailTakeActionDetail | +------------------------------------+ Figure 21. SUPAHasPolExecFailTakeAction Association 5.3.2.6.1. The Attribute "supaPolExecFailActionEncoding" This is an optional enumerated, non-negative integer attribute that defines how to find the set of SUPAPolicyActions contained in each element of the supaPolExecFailTakeActionName class attribute. Values include: 0: error 1: init 2: URI 3: GUID 4: UUID 5: FQDN 6: FQPN 7: string 8: string_instance_id Strassner, et al. Expires November 30, 2017 [Page 61]
Internet-Draft SUPA Generic Policy Model May 2017 The values 0 and 1 represent an error state and an initialization state, respectively. Values 2-6 define a representation for the SUPAPolicyAction. A value of 7 defines an ASCII string that contains the name of the SUPAPolicyAction to be executed (e.g., to be used in a regex search). A value of 8 defines the canonical representation, in ASCII, of an instance ID of this object. 5.3.2.6.2. The Attribute "supaPolExecFailActionName[1..n]" This is an optional array of string attributes that identifies the set of SUPAPolicyActions to take if the SUPAPolicyStructure object that owns this association failed to execute properly. The interpretation of this string attribute is defined by the supaPolExecFailTakeActionEncoding class attribute. The association defines the SUPAPolicyStructure that contains the set of policy actions to execute, and this attribute defines which of these actions are to be executed. That there is no need to execute a SUPAPolicy, since the event and failure have already occurred. Note: [1..n] means that this is a multi-valued property that has at least one (and possibly more) attributes. 5.3.2.7. The Aggregation "SUPAHasPolicyClause" This is an optional aggregation that defines the set of SUPAPolicyClauses that are aggregated by this particular SUPAPolicyStructure instance. The semantics of this aggregation are defined by the SUPAHasPolicyClauseDetail association class. Every SUPAPolicyStructure object instance MUST aggregate at least one SUPAPolicyClause object instance. However, the converse is NOT true. For example, a SUPAPolicyClause could be instantiated and then stored for later use in a policy repository. Furthermore, the same SUPAPolicyClause could be used by zero or more SUPAPolicyStructure object instances at a given time. Thus, the multiplicity of this aggregation is defined as 0..1 on the aggregate (i.e., the SUPAPolicyStructure side) and 1..n on the part (i.e., the SUPAPolicyClause side). This means that at least one SUPAPolicyClause MUST be aggregated by this SUPAPolicyStructure object. Similarly, a SUPAPolicyClause may be aggregated by this particular SUPAPolicyStructure object. Strassner, et al. Expires November 30, 2017 [Page 62]
Internet-Draft SUPA Generic Policy Model May 2017 5.3.2.8. The Association Class "SUPAHasPolicyClauseDetail" This is an optional abstract association class, and defines the semantics of the SUPAHasPolicyClause aggregation. The attributes and/or relationships of this association class can be used to determine which SUPAPolicyClauses are aggregated by which SUPAPolicyStructure objects. 5.4. The Abstract Class "SUPAPolicyComponentStructure" This is a mandatory abstract class. It is the superclass of all objects that represent different types of components of a SUPAPolicy. Different types of policies have different types of structural components. This is accommodated by defining two generic abstract subclasses, called SUPAPolicyClause and SUPAPolicyClauseComponentDecorator, which are both common to different policy types. These two classes represent convenient control points for defining characteristics and behavior that are common to objects that serve as components of a SUPAPolicy. SUPAPolicyClause defines a basic building block for writing parts of a SUPAPolicy. It is analogous to a clause in a sentence. For example, in an ECA Policy Rule, the Event, Condition, and Action clauses are each made up of at least one (concrete subclass of a) SUPAPolicyClause. Similalry, declarative Policy Rules can also be defined using (its own subclasses of) SUPAPolicyClauses. This class is defined in section 5.5. SUPAPolicyClauseComponentDecorator implements the decorator pattern [11]. The decorator pattern enables all or part of one or more objects to "wrap" another concrete object (as described in Section 4.2.1.2). This enables the definition of an extensible set of subclasses that can augment the definition of a SUPAPolicyClause. This class is defined in section 5.7. Note that there are significant differences between the definition of the SUPAPolicyComponentStructure class, and its attributes and relationships, and the definition of the corresponding class (and its attributes and relationships) in [5]. 5.4.1. SUPAPolicyComponentStructure Attributes No attributes are currently defined for this class. 5.4.2. SUPAPolicyComponentStructure Relationships SUPAPolicyComponentStructure participates in a single relationship, SUPAHasDecoratedPolicyComponent, as defined in section 5.7.3. It also inherits the SUPAHasPolicyMetadata aggregation (see section 5.17.2.1.). Strassner, et al. Expires November 30, 2017 [Page 63]
Internet-Draft SUPA Generic Policy Model May 2017 5.5. The Abstract Class "SUPAPolicyClause" This is a mandatory abstract class that separates the representation of a SUPAPolicy from its implementation. SUPAPolicyClause was abstracted from DEN-ng [2]. This abstraction is missing in [RFC3060], [RFC3460], [4], and [6]. This class is called PolicyStatement in [5], but the class and relationship definitions differ significantly from the corresponding designs in this document. A SUPAPolicy, regardless of its structure and semantics, can be abstracted into a set of sentences. Each sentence can in turn be abstracted into a set of clauses. A SUPAPolicyClause is, as its name implies, a clause (i.e., a part of a statement), and defines the content of a SUPAPolicy. The decorator pattern is used to enable an extensible set of objects to "wrap" the SUPAPolicyClause; this enables the contents of a SUPAPolicyClause to be adjusted dynamically at runtime without affecting other objects. This document defines two different types of policy clauses: SUPAEncodedClause (which is generic, and can be used by any type of policy), and SUPABooleanClause (which is also generic, but is typically used by SUPAECAPolicyRule objects, since it is used specifically to represent Boolean clauses). SUPAPolicyClauses are objects in their own right, which facilitates their reuse. SUPAPolicyClauses can aggregate a set of any of the subclasses of SUPAPolicyClauseComponentDecorator; this was shown in Figures 12 and 13. These five subclasses (i.e., SUPAPolicyTerm, SUPAGenericDecoratedComponent, SUPAECAComponent, SUPACollection, and SUPAPolicyComponentDecorator) provide several different ways to construct a SUPAPolicyClause: 1) a SUPAPolicyClause can be made up of a set of three SUPAPolicyTerms, which enables constructing an expression consiting of a {variable, operator, value} 3-tuple, for building SUPAPolicyClauses 2) a SUPAPolicyClause can be made up of one or more SUPAEncodedClauses, which enables a SUPAPolicyClause to be formed as an encoded object (e.g., to pass YANG or CLI code) 3) a SUPAPolicyClause can be made up of a set of SUPACollections, which define a Collection (e.g., set, bad, associative arrays) of objects that can be assembled into SUPAPolicyClauses after further processing 4) a SUPAPolicyClause can be made up of one or more SUPAECAComponents, which enables a SUPAPolicyClause to be formed using (reusable) Event, Condition, and/or Action objects 5) any or all of the above methods can be augmented with more complex decorated structures using SUPAPolicyComponentDecorator Strassner, et al. Expires November 30, 2017 [Page 64]
Internet-Draft SUPA Generic Policy Model May 2017 SUPAPolicyClauses are formed by aggregating a set of concrete subclasses of the SUPAPolicyClauseComponentDecorator class using the SUPAPolicyClauseHasDecorator aggregation (see Figure 12). The resulting SUPAPolicyClause is then aggregated by a concrete subclass of the SUPAPolicyStructure class, which enables a SUPAPolicy to be made up of one or more SUPAPolicyClauses. 5.5.1. SUPAPolicyClause Attributes This section defines the attributes of the SUPAPolicyClause class, which are inherited by all SUPAPolicyClause subclasses. 5.5.1.1. The Attribute "supaPolClauseDeployStatus" This is an optional enumerated, non-negative integer attribute. The purpose of this attribute is to indicate that this SUPAPolicyClause can or cannot be deployed by the policy management system. This attribute enables the policy manager to know which SUPAPolicyClauses to retrieve, and may be useful for the policy execution system for planning the staging of SUPAPolicies. Values include: 0: error 1: init 2: deployed and enabled 3: deployed and in test 4: deployed but not enabled 5: ready to be deployed 6: cannot be deployed The values 0 and 1 represent an error state and an initialization state, respectively. If the value of this attribute is 0 or 6, then the policy management system SHOULD ignore this SUPAPolicy. Otherwise, the policy management system MAY use this SUPAPolicyClause (once this SUPAPolicyClause is deployed and enabled). However, a value of 4 means that this policy is not admininstratively enabled for use and SHOULD NOT be used in OAM&P policies. 5.5.2. SUPAPolicyClause Relationships SUPAPolicyClause participates in two relationships. The first, SUPAHasPolicyClause, was defined in section 5.3.2.7. The second, SUPAPolicyClauseHasDecorator, is defined below. Note that SUPAPolicyClause uses the SUPAPolicyClauseHasDecorator aggregation to implement the decorator pattern; this enables a SUPAPolicyClause to be "wrapped" with instances of the (concrete) subclasses of the SUPAPolicyClauseComponentDecorator object. Strassner, et al. Expires November 30, 2017 [Page 65]
Internet-Draft SUPA Generic Policy Model May 2017 5.5.2.1. The Aggregation "SUPAPolicyClauseHasDecorator" This is a mandatory aggregation, and is part of a decorator pattern. It is used to enable a concrete instance of a SUPAPolicyClauseComponentDecorator to dynamically add behavior to a specific type (of concrete subclass) of a SUPAPolicyClause object. The semantics of this aggregation are defined by the SUPAPolicyClauseHasDecoratorDetail association class. The multiplicity of this aggregation is 0..n - 0..n. This means that a SUPAPolicyClause does not have to be decorated; however, if it is, then zero or more concrete subclasses of the SUPAPolicyClauseComponentDecorator class may be used to decorate the concrete subclass of SUPAPolicyClause. 5.5.2.2. The Association Class "SUPAPolicyClauseHasDecoratorDetail" This is a mandatory concrete association class, and defines the semantics of the SUPAPolicyClauseHasDecorator aggregation. The purpose of this class is to use the Decorator pattern to determine which SUPAPolicyClauseComponentDecorator object instances, if any, are required to augment the functionality of the concrete subclass of the SUPAPolicyClause that is being used. Currently, there are two attributes defined for this class, which are described in the following subsections. Both attributes are used in this association class to **constrain the relationship** between the concrete subclass of SUPAPolicyClauseComponentDecorator that is wrapping the concrete subclass of SUPAPolicyClause. Note that class attributes of SUPAPolicyClauseComponentDecorator (see section 5.9.2) only affect that specific subclass. 5.5.2.2.1. The Attribute "supaPolClauseDecConstraintEncoding" This is a mandatory non-negative enumerated integer that defines how to interpret each string in the supaPolClauseDecConstraint class attribute. Values include: 0: error 1: init 2: OCL 2.4 3: OCL 2.x 4: OCL 1.x 5: QVT 1.2 - Relations Language 6: QVT 1.2 - Operational language 7: Alloy 8: ASCII Text Strassner, et al. Expires November 30, 2017 [Page 66]
Internet-Draft SUPA Generic Policy Model May 2017 Enumerations 0 and 1 signify an error state and an initialization state, respectively. Enumerations 2-4 are dedicated to OCL (with OCL 2.4 being the latest version as of this writing). QVT defines a set of languages [20] (the two most powerful and useful are defined by enumerations 5 and 6). Alloy is a language for describing constraints, and uses a SAT solver to guarantee correctness [21]. Enumeration 8 (ASCII Text) is not recommended (since it is informal, and hence, not verifiable), but is included for completeness. 5.5.2.2.2. The Attribute "supaPolClauseDecConstraint[0..n]" This is a mandatory array of string attributes. Each attribute specifies a constraint to be applied using the encoding defined in the supaPolCompConstraintEncoding class attribute. This provides a more rigorous and flexible treatment of constraints than is possible in [RFC3460], [4], [5], and [6]. Note: [0..n] means that this is a multi-valued property that may have zero or more attributes. 5.6. The Concrete Class "SUPAEncodedClause" This is a mandatory concrete class that refines the behavior of a SUPAPolicyClause. This class defines a generalized extension mechanism for representing SUPAPolicyClauses that have not been modeled with other SUPAPolicy objects. This class encodes the contents of the policy clause directly into the attributes of the SUPAEncodedClause. Hence, SUPAEncodedClause objects are reusable at the object level, whereas SUPABooleanClause clauses are reusable at the individual Boolean expression level. This class uses two of its attributes (supaEncodedClauseContent and supaEncodedClauseEncoding) for defining the content and type of encoding used in a given SUPAPolicyClause. The benefit of a SUPAEncodedClause is that it enables direct encoding of the text of the SUPAPolicyClause, without having the "overhead" of using other objects. However, note that while this method is efficient, it does not reuse other SUPAPolicy objects. Furthermore, its potential for reuse is reduced, as only SUPAPolicies that can use the exact encoding of this clause can reuse this object. 5.6.1. SUPAEncodedClause Attributes This section defines the attributes of the SUPAEncodedClause class. Prescriptive and/or descriptive information about the usage of this SUPAEncodedClause may be provided by one or more SUPAPolicyMetadata objects, which are each attached to the object instance of this SUPAEncodedClause. Strassner, et al. Expires November 30, 2017 [Page 67]
Internet-Draft SUPA Generic Policy Model May 2017 5.6.1.1. The Attribute "supaEncodedClauseContent" This is a mandatory string attribute, and defines the content of this clause. It works with another class attribute, called supaEncodedClauseEncoding, which defines how to interpret the value of this attribute (e.g., as a string or reference). These two attributes form a tuple, and together enable a machine to understand the syntax and value of this object instance. 5.6.1.2. The Attribute "supaEncodedClauseEncoding" This is a mandatory non-negative integer attribute, and defines how to interpret the value of the supaEncodedClauseContent. It works with another class attribute (supaEncodedClauseContent), which defines the content of the encoded clause. These two attributes form a tuple, and together enable a machine to understand the syntax and value of the encoded clause for the object instance of this class. This attribute is NOT required in all data model implementations. Values include: 0: error (i.e., an error state) 1: init (i.e., an initialization state) 2: primary_key 3: foreign_key 4: GUID 5: UUID 6: URI 7: FQDN 8: FQPN 9: string_instance_id The values 0 and 1 represent an error state and an initialization state, respectively. The value 9 defines the canonical representation, in ASCII, of an instance ID of this object. 5.6.1.3. The Attribute "supaEncodedClauseLanguage" This is mandatory non-negative integer attribute, and defines the type of language used in this encoded clause. Values include: 0: error 1: init 2: Text 3: YANG 4: XML 5: TL1 The values 0 and 1 represent an error state and an initialization state, respectively. Strassner, et al. Expires November 30, 2017 [Page 68]
Internet-Draft SUPA Generic Policy Model May 2017 5.6.1.4. The Attribute "supaEncodedClauseResponse" This is an optional Boolean attribute that emulates a Boolean response of this clause, so that it may be combined with other subclasses of the SUPAPolicyClause that provide a status as to their correctness and/or evaluation state. This enables this object to be used to construct more complex Boolean clauses. Note that this attribute does NOT have to be implemented by all data model implementations (e.g., [15]). 5.6.2. SUPAEncodedClause Relationships SUPAPolicyClause participates in two inherited relationships. These are SUPAHasPolicyClause, as defined in section 5.3.2.7, and SUPAPolicyClauseHasDecorator, as defined in section 5.7.2. 5.7. The Abstract Class "SUPAPolicyClauseComponentDecorator" This is a mandatory class, and is used to implement the decorator pattern. The decorator pattern enables all or part of one or more objects to "wrap" another concrete object. This means that any any concrete subclass of SUPAPolicyClause can be wrapped by any concrete subclass of SUPAPolicyClauseComponentDecorator, as shown in Figure 22 below. SUPAHasPolicyClause +----------------+----------------------------+ | ^ | | | | | C | | | +-------------+----------------------+ | | | SUPAPolicyClauseHasDecoratorDetail | | | +-------------+----------------------+ | | | | | / \ | A | A \ / 0..n A \ / 1..n +--------+-----------+ +---------------------------+--------+ | SUPAPolicyClause | | SUPAPolicyClauseComponentDecorator | +----------+---------+ +--------------+---------------------+ I I I I / \ / \ Concrete Subclasses, Concrete Subclasses (e.g., SUPAEncodedClause) (e.g., SUPAPolicyEvent) that are being wrapped that are the wrapping object(s) Figure 22. SUPAPolicyClauseComponentDecorator Strassner, et al. Expires November 30, 2017 [Page 69]
Internet-Draft SUPA Generic Policy Model May 2017 The SUPAHasPolicyClause aggregation enables one or more concrete subclasses of SUPAPolicyClauseComponentDecorator to wrap a concrete subclass of SUPAPolicyClause. Its semantics are defined by the SUPAPolicyClauseHasDecoratorDetail association class. 5.7.1. SUPAPolicyClauseComponentDecorator Attributes Currently, there are two attributes defined for this class, which are described in the following subsections. Both attributes are used by subclasses to **constrain the behavior of that subclass**; they do **not** affect the relationship between the concrete subclass of SUPAPolicyClauseComponentDecorator that is wrapping the concrete subclass of SUPAPolicyClause. This is different than the use of similar attributes defined in the SUPAPolicyClauseHasDecoratorDetail association class. The attributes of SUPAPolicyClauseComponentDecorator are used to constrain the (concrete subclass of) SUPAPolicyClause that this SUPAPolicyClauseComponentDecorator is wrapping. In contrast, the attributes of SUPAPolicyClauseHasDecoratorDetail are used to define which concrete subclasses of SUPAPolicyClause can be wrapped by which concrete subclasses of SUPAPolicyClauseComponentDecorator. 5.7.1.1. The Attribute "supaPolClauseConstraintEncoding" This is a mandatory non-negative enumerated integer that defines how to interpret each string in the supaPolCompConstraint class attribute. Values include: 0: error 1: init 2: OCL 2.4 3: OCL 2.x 4: OCL 1.x 5: QVT 1.2 - Relations Language 6: QVT 1.2 - Operational language 7: Alloy 8: ASCII Text Enumerations 0 and 1 signify an error state and an initialization state, respectively. Enumerations 2-4 are dedicated to OCL (with OCL 2.4 being the latest version as of this writing). QVT defines a set of languages [20] (the two most powerful and useful are defined by enumerations 5 and 6). Alloy is a language for describing constraints, and uses a SAT solver to guarantee correctness [21]. Enumeration 8 (ASCII Text) is not recommended (since it is informal, and hence, not verifiable), but is included for completeness. Strassner, et al. Expires November 30, 2017 [Page 70]
Internet-Draft SUPA Generic Policy Model May 2017 5.7.1.2. The Attribute "supaPolClauseConstraint[0..n]" This is a mandatory array of string attributes. Each attribute specifies a constraint to be applied using the encoding defined in the supaPolCompConstraintEncoding class attribute. This provides a more rigorous and flexible treatment of constraints than is possible in [RFC3460], [4], [5], and [6]. Note: [0..n] means that this is a multi-valued property that may have zero or more attributes. 5.7.2. SUPAPolicyClauseComponentDecorator Relationships This class currently participates in two relationships. The first, SUPAPolicyClauseHasDecorator, was defined in Section 5.5.2. The second, SUPAHasDecoratedPolicyComponent, is defined in Section 5.14.2. 5.7.3. Illustration of Constraints in the Decorator Pattern Figure 23 builds a simple SUPAPolicyClause that has both types of relationships, and illustrates how the different constraints defined in sections 5.7.2 (class attribute constraints) and section 5.7.3 (relationship constraints) can be used. A A +----------------+ 0..1 +----------------------------------+ | | 1..n / \| | |SUPAPolicyClause+------+---- A +SUPAPolicyClauseComponentDecorator| | | ^ \ /| | +---------+------+ | +-----------+----------------------+ / \ | / \ I | I I | I C I | C I +--------+--------+ | +---------+---------+ |SUPAEncodedClause| | | SUPAPolicyEvent | +-----------------+ | +-------------------+ | C | +---------------+------------+ |SUPAPolicyHasDecoratorDetail| +----------------------------+ Figure 23. Constraints in the Decorator Pattern Figure 23 says that a SUPAPolicyClause, realized as a SUPAEncodedClause object, is wrapped by a SUPAPolicyClauseComponentDecorator, realized as a SUPAPolicyEvent object. The attributes in the SUPAPolicyClauseComponentDecorator object, which are inherited by the SUPAPolicyEvent object, are used to constrain the behavior of the SUPAPolicyEvent object. Strassner, et al. Expires November 30, 2017 [Page 71]
Internet-Draft SUPA Generic Policy Model May 2017 Put another way, the SUPAPolicyClauseHasDecorator aggregation enables a concrete subclass of SUPAPolicyClause to be decorated by concrete subclasses of SUPAPolicyClauseComponentDecorator. The decorator pattern is implemente by the SUPAHasDecoratedPolicyComponent aggregation. Hence, attributes in the SUPAHasDecoratedPolicyComponentDetail association class are used to contrain the behavior of the decorator (e.g., restricting which concrete subclasses of the SUPAPolicyComponentDecorator can be used as decorators). For example, the attributes in the SUPAPolicyClauseComponentDecorator class, when instantiated in an instance of a concrete subclass, could restrict which SUPAPolicyEvent objects are allowed to be used with which SUPAEncodedClause objects. 5.8. The Abstract Class "SUPAPolicyTerm" This is a mandatory abstract class that is the parent of SUPAPolicy objects that can be used to define a standard way to test or set the value of a variable. It does this by defining a 3-tuple, in the form {variable, operator, value}, where each element of the 3-tuple is defined by a concrete subclass of the appropriate type (i.e., SUPAPolicyVariable, SUPAPolicyOperator, and SUPAPolicyValue classes, respectively). For example, a generic test or set of the value of a variable is expressed as: {variable, operator, value}. For event and condition clauses, this is typically as written above (e.g., does variable = value); for action clauses, it is typically written as <operator> <variable> <value> (e.g., SET var to 1). A class diagram is shown in Figure 24. A +----------------+ | SUPAPolicyTerm | +--------+-------+ / \ I I I +-----------------+---+--------------------+ I I I I I I C I C I C I +--------+---------+ +--------+---------+ +-------+-------+ |SUPAPolicyVariable| |SUPAPolicyOperator| |SUPAPolicyValue| +------------------+ +------------------+ +---------------+ Figure 24. SUPAPolicyTerm Class Hierarchy Strassner, et al. Expires November 30, 2017 [Page 72]
Internet-Draft SUPA Generic Policy Model May 2017 Note that generic test and set expressions do not have to only use objects that are subclasses of SUPAPolicyTerm. For example, the supaGenericDecoratedCompContent attribute of the SUPAGenericDecoratedComponent could be used as the variable (or the value) term of a get or set expression that is in the above form. Hence, the utility of the subclasses of SUPAPolicyTerm is in the ability of its subclasses to define a generic framework for implementing get and set expressions. This is in contrast to previous designs (e.g., [RFC3460] and [6]), which depended on defining a broad set of subclasses of PolicyVariable and PolicyValue. (Note that [4] does not have this generic capability). 5.8.1. SUPAPolicyTerm Attributes Currently, SUPAPolicyTerm defines a single attribute, as described in the following subsection. Constraints on the subclasses of SUPAPolicyTerm can be applied in two different ways: 1. use SUPAPolicyComponentDecorator attributes to constrain just that individual subclass, and/or 2. use SUPAHasDecoratedPolicyComponentDetail association class attributes to constrain the relationship between the concrete subclass of SUPAPolicyClause and the concrete subclass of the SUPAPolicyTerm class; this determines which concrete subclasses of SUPAPolicyTerm can be used to construct this particular SUPAPolicyClause. 5.8.1.1. The Attribute "supaPolTermIsNegated" This is a mandatory Boolean attribute. If the value of this attribute is true, then this particular SUPAPolicyTerm subclass (which represents a term) is negated; otherwise, it is not. 5.8.2. SUPAPolicyTerm Relationships Currently, no dedicated relationships are defined for the SUPAPolicyTerm class (as there are in [RFC3460] and [6]) that aggregate policy variable and policy value objects into a policy rule). This is: 1) to enable the subclasses of SUPAPolicyTerm to be used by other SUPAPolicyComponentDecorator objects, and 2) because the decorator pattern replaces how such relationships were used in [RFC3460] and [6]. SUPAPolicyTerm, and its subclasses, inherit the SUPAPolicyClauseHasDecorator aggregation, which was defined in Section 5.5.2, as well as the SUPAHasDecoratedPolicyComponent aggregation, which was defined in section 5.7.3. Strassner, et al. Expires November 30, 2017 [Page 73]
Internet-Draft SUPA Generic Policy Model May 2017 5.9. The Concrete Class "SUPAPolicyVariable" This is a mandatory concrete class that defines information that forms a part of a SUPAPolicyClause. It specifies a concept or attribute that represents a variable, which should be compared to a value, as specifed in this SUPAPolicyClause. If it is used in a SUPAECAPolicyRule, then its value MAY be able to be changed at any time, including run-time, via use of the decorator pattern. This is not possible in previous designs ([RFC3460, [4], and [6]). The value of a SUPAPolicyVariable is typically compared to the value of a SUPAPolicyValue using the type of operator defined in a SUPAPolicyOperator. However, other objects may be used instead of a SUPAPolicyValue object, and other operators may be defined in addition to those defined in the SUPAPolicyOperator class. SUPAPolicyVariables are used to abstract the representation of a SUPAPolicyClause from its implementation. Some SUPAPolicyVariables are restricted in the values and/or the data type that they may be assigned. For example, port numbers cannot be negative, and they cannot be floating-point numbers. These and other constraints may be defined in two different ways: 1. use SUPAPolicyClauseComponentDecorator attributes to constrain just that individual object, and/or 2. use the SUPAPolicyClauseHasDecoratorDetail association class attributes to constrain the relationship between the concrete subclass of SUPAPolicyClause and the concrete subclass of the SUPAPolicyVariable class Please refer to the examples in section 7, which show how to restrict the value, data type, range, and other semantics of the SUPAPolicyVariable when used in a SUPAPolicyClause. 5.9.1. Problems with the RFC3460 Version of PolicyValue Please see Appendix A for a detailed comparison. 5.9.2. SUPAPolicyVariable Attributes SUPAPolicyVariable defines one attribute, as described below. 5.9.2.1. The Attribute "supaPolVarName" This is an optional string attribute that contains the name of this SUPAPolicyVariable. This variable name forms part of the {variable, operator, value} canonical form of a SUPAPolicyClause. Strassner, et al. Expires November 30, 2017 [Page 74]
Internet-Draft SUPA Generic Policy Model May 2017 5.9.3. SUPAPolicyVariable Relationships Currently, no relationships are defined for the SUPAPolicyVariable class (note that the decorator pattern obviates the need for relationships such as those defined in [RFC3460] and [6]). This is because SUPAPolicyVariable, and its subclasses, inherit the SUPAHasDecoratedPolicyComponent aggregation, which was defined in section 5.7.3. 5.10. The Concrete Class "SUPAPolicyOperator" This is a mandatory concrete class for modeling different types of operators that are used in a SUPAPolicyClause. The restriction of the type of operator used in a SUPAPolicyClause restricts the semantics that can be expressed in that SUPAPolicyClause. It is typically used with SUPAPolicyVariables and SUPAPolicyValues to form a SUPAPolicyClause. 5.10.1. Problems with the RFC3460 Version Please see Appendix A for a detailed comparison. 5.10.2. SUPAPolicyOperator Attributes Currently, SUPAPolicyOperator defines a single generic attribute, as described below. 5.10.2.1. The Attribute "supaPolOpType" This is a mandatory non-negative enumerated integer that specifies the various types of operators that are allowed to be used in this particular SUPAPolicyClause. Values include: 0: error 1: init 2: Greater than 3: Greater than or equal to 4: Less than 5: Less than or equal to 6: Equal to 7: Not equal to 8: IN 9: NOT IN 10: SET 11: CLEAR (0 for integers, "" for strings, FALSE for Booleans) 12: BETWEEN (inclusive) 13: regular expression, PERL-based 14: regular expression, POSIX-based (BRE, basic) 15: regular expression, POSIX-based (ERE, extended) Strassner, et al. Expires November 30, 2017 [Page 75]
Internet-Draft SUPA Generic Policy Model May 2017 Note that 0 and 1 represent error and initialization states, respectively. Their purpose is to support dynamically building a SUPAPolicyClause by enabling the application to set the value of this attribute to a standard value. This list has been influenced by the work in the I2NSF WG. Specifically, references [22] and [23] categorize selectors as exact-match, range-based, regular expressions, and custom match. In this categorization, the values in the above enumeration are mapped as follows: o "Exact-match" is used to check for equality. The result is an unstructured unordered set. This includes values 6 and 7. o "Range-based" are **ordered** sets, where ranges that map to integers are used. This includes values 2-5, 8, 9, and 12. o "Regular expressions", which include the use of special characters that collectively define a search pattern. Two different syntaxes are specified; they are documented in [24] (for value 14) and [25]. This maps to values 13-15. Note that POSIX-based simple regular expressions (SRE) are **deprecated** by POSIX-based basic regular expressions (BRE). Additional operators may be defined in future work. For example, if SUPAPolicyVariables and SUPAPolicyValues are expanded to/from include structured objects, then "deep" versions of operators 1-6 could also be defined. In this case, values 1-6 will be edited to explicitly indicate that they perform "shallow" comparison operations. 5.10.3. SUPAPolicyOperator Relationships Currently, no relationships are defined for the SUPAPolicyOperator class (note that the decorator pattern obviates the need for relationships such as those in [6]). This is because SUPAPolicyOperator, and its subclasses, inherit the SUPAHasDecoratedPolicyComponent aggregation, which was defined in section 5.7.3. Please refer to the examples in section 7, which show how to restrict the value, data type, range, and other semantics of the SUPAPolicyOperator when used in a SUPAPolicyClause. 5.11. The Concrete Class "SUPAPolicyValue" The SUPAPolicyValue class is a mandatory concrete class for modeling different types of values and constants that occur in a SUPAPolicyClause. SUPAPolicyValues are used to abstract the representation of a SUPAPolicyRule from its implementation. Therefore, the design of SUPAPolicyValues depends on two important factors. Strassner, et al. Expires November 30, 2017 [Page 76]
Internet-Draft SUPA Generic Policy Model May 2017 First, just as with SUPAPolicyVariables (see Section 5.9), some types of SUPAPolicyValues are restricted in the values and/or the data type that they may be assigned. Second, there is a high likelihood that specific applications will need to use their own variables that have specific meaning to a particular application. In general, there are two ways to apply constraints to an object instance of a SUPAPolicyValue: 1. use SUPAPolicyClauseComponentDecorator attributes to constrain just that individual object, and/or 2. use the SUPAPolicyClauseHasDecoratorDetail association class attributes to constrain the relationship between the concrete subclass of SUPAPolicyClause and the concrete subclass of the SUPAPolicyVariable class The value of a SUPAPolicyValue is typically compared to the value of a SUPAPolicyVariable using the type of operator defined in a SUPAPolicyOperator. However, other objects may be used instead of a SUPAPolicyVariable object, and other operators may be defined in addition to those defined in the SUPAPolicyOperator class. Please refer to the examples in section 7, which show how to restrict the value, data type, range, and other semantics of the SUPAPolicyVariable when used in a SUPAPolicyClause. 5.11.1. Problems with the RFC3460 Version of PolicyValue Please see Appendix A for a detailed comparison. 5.11.2. SUPAPolicyValue Attributes Currently, SUPAPolicyValue defines two generic attributes, as described below. 5.11.2.1. The Attribute "supaPolValContent[0..n]" This is a mandatory attribute that defines an array of strings. The array contains the value(s) of this SUPAPolicyValue object instance. Its data type is defined by the supaPolValEncoding class attribute. Note: [0..n] means that this is a multi-valued property that has zero or more attributes. 5.11.2.2. The Attribute "supaPolValEncoding" This is a mandatory string attribute that contains the data type of the SUPAPolicyValue object instance. Its value is defined by the supaPolValContent class attribute. Values include: Strassner, et al. Expires November 30, 2017 [Page 77]
Internet-Draft SUPA Generic Policy Model May 2017 0: error 1: init 2: String 3: Integer 4: Boolean 5: Floating Point 6: DateTime 7: GUID 8: UUID 9: URI 10: DN 11: FQDN 12: FQPN 13: NULL Note that 0 and 1 represent error and initialization states, respectively. A string is a sequence of zero or more characters. An Integer is a whole number, and has no fractional part. A Boolean may take the values TRUE and FALSE. A floating point number may contain fractional values, as well as an exponent. A DateTime represents a value that has a date and/or a time component (as in the Java or Python libraries). A NULL explicitly models the lack of a value. 5.11.3. SUPAPolicyValue Relationships Currently, no relationships are defined for the SUPAPolicyValue class (note that the decorator pattern obviates the need for relationships such as those in [6]). SUPAPolicyValue, and its subclasses, inherit the SUPAHasDecoratedPolicyComponent aggregation, which was defined in section 5.7.3. Please refer to the examples in section 7, which show how to restrict the value, data type, range, and other semantics of the SUPAPolicyValue when used in a SUPAPolicyClause. 5.12. The Concrete Class "SUPAGenericDecoratedComponent" A SUPAGenericDecoratedComponent enables a generic object to be defined and used in a SUPAPolicyClause. This class was derived from [2], but is not present in [RFC3460], [4], [5], or [6]. This class should not be confused with the SUPAEncodedClause class. The SUPAGenericDecoratedComponent class represents a single, atomic object that defines a **portion** of a SUPAPolicyClause, whereas a SUPAEncodedClause represents an **entire** SUPAPolicyClause. 5.12.1. SUPAGenericDecoratedComponent Attributes Currently, SUPAGenericDecoratedComponent defines two generic attributes, as described below. Strassner, et al. Expires November 30, 2017 [Page 78]
Internet-Draft SUPA Generic Policy Model May 2017 5.12.1.1. The Attribute "supaGenericDecoratedCompContent[0..n]" This is a mandatory attribute that defines an array of strings. This array contains the value(s) of the SUPAGenericDecoratedComponent object instance that are used to construct a portion of a SUPAPolicyClause. Its data type is defined by the supaGenericDecoratedCompEncoding class attribute. Note: [0..n] means that this is a multi-valued property that has zero or more attributes. 5.12.1.2. The Attribute "supaGenericDecoratedCompEncoding" This is a mandatory integer attribute that defines the format of the supaGenericDecoratedCompContent class attribute. Values include: 0: error 1: init 2: String 3: Integer 4: Boolean 5: Floating Point 6: DateTime 7: GUID 8: UUID 9: URI 10: DN 11: FQDN 12: FQPN 13: NULL Note that 0 and 1 represent error and initialization states, respectively. A string is a sequence of zero or more characters. An Integer is a whole number, and has no fractional part. A Boolean may take the values TRUE and FALSE. A floating point number may contain fractional values, as well as an exponent. A DateTime represents a value that has a date and/or a time component (as in the Java or Python libraries). A NULL explicitly models the lack of a value. 5.12.2. SUPAGenericDecoratedComponent Relationships Currently, no relationships are defiend for the SUPAGenericDecoratedComponent class (note that the decorator pattern obviates the need for relationships such as those in [6]). SUPAGenericDecoratedComponent participates in a single relationship, SUPAHasDecoratedPolicyComponent, as defined in section 5.7.3. Strassner, et al. Expires November 30, 2017 [Page 79]
Internet-Draft SUPA Generic Policy Model May 2017 5.13. The Concrete Class "SUPAPolicyCollection" A SUPAPolicyCollection is an optional concrete class that enables a collection (e.g., set, bag, or other, more complex, collections of elements) of **arbitrary objects** to be defined and used as part of a SUPAPolicyClause. This class was derived from [2], but is not present in [RFC3460], [4], [5], or [6]. 5.13.1. Motivation One of the problems with ECA policy rules is when an enumeration occurs in the event and/or condition clauses. For example, if a set of events is received, the policy system may need to wait for patterns of events to emerge (e.g., any number of Events of type A, followed by either one event of type B or two events of type Event C). Similarly, for conditions, testing the value of a set of attributes may need to be performed. Both of these represent behavior similar to a set of if-then-else statements or a switch statement in imperative programming languages. It is typically not desirable for the policy system to represent each choice in such clauses as its own policy clause (i.e., a 3-tuple), as this creates object explosion and poor performance. Furthermore, in these cases, it is often required to have a set of complex logic to be executed, where the logic varies according to the particular event or condition that was selected. It is much too complex to represent this using separate objects, especially when the logic is application- and/or vendor-specific. However, recall that one of the goals of this document was to facilitate the machine-driven construction of policies. Therefore, a solution to this problem is needed. 5.13.2. Solution Therefore, this document defines the concept of a collection of entities, called a SUPAPolicyCollection. Conceptually, the items to be collected (e.g., events or conditions) are aggregated in one or more SUPAPolicyCollection objects of the appropriate type. Another optional SUPAPolicyCollection object could be used to aggregate logic blocks (including SUPAPolicies) to execute. Once finished, all appropriate SUPAPolicyCollection objects are sent to an external system for evaluation. The computation(s) represented by the SUPAPolicyCollection may be part of a larger SUPAPolicyClause, since SUPAPolicyCollection is a subclass of SUPAPolicyComponentDecorator, and can be used to decorate a SUPAPolicyClause. Therefore, the external system is responsible for providing a Boolean TRUE or FALSE return value, so that the policy system can use that value to represent the computation of the function(s) performed in the SUPAPolicyCollection in a Boolean clause. Strassner, et al. Expires November 30, 2017 [Page 80]
Internet-Draft SUPA Generic Policy Model May 2017 5.13.3. SUPAPolicyCollection Attributes Currently, SUPAGenericDecoratedComponent defines five attributes, as described below. 5.13.3.1. The Attribute "supaPolCollectionContent[0..n]" This is an optional attribute that defines an array of strings. Each string in the array defines a domain-suitable identifier of an object that is collected by this SUPAPolicyCollection instance. Note: [0..n] means that this is a multi-valued property that has zero or more attributes. 5.13.3.2. The Attribute "supaPolCollectionEncoding" This is a mandatory non-negative enumerated integer that defines the format of the identifier of all objects in this collection instance. Values include: 0: error (i.e., an error state) 1: init (i.e., an initialization state) 2: primary_key 3: foreign_key 4: GUID 5: UUID 6: URI 7: FQDN 8: FQPN 9: string_instance_id Note that 0 and 1 represent error and initialization states, respectively. Values 2-8 define the content as a reference. The value 9 defines the canonical representation, in ASCII, of an instance ID of this object. 5.13.3.3. The Attribute "supaPolCollectionFunction" This is an optional non-negative enumerated integer that defines the function of this collection instance. Values include: 0: error 1: init 2: event collection 3: condition collection 4: action collection 5: processing logic collection Strassner, et al. Expires November 30, 2017 [Page 81]
Internet-Draft SUPA Generic Policy Model May 2017 Note that 0 and 1 represent error and initialization states, respectively. Values 2-4 define a collection of objects that are to be used to populate the event, condition, or action clauses, respectively, of a SUPAECAPolicyRule. A value of 5 indicates that this collection contains objects that define logic for processing a SUPAPolicy. 5.13.3.4. The Attribute "supaPolCollectionIsOrdered" This is an optional Boolean attribute. If the value of this attribute is TRUE, then all elements in this instance of this SUPAPolicyCollection are ordered. 5.13.3.5. The Attribute "supaPolCollectionType" This is an optional non-negative enumerated integer that defines the type of collection that this instance is. Values include: 0: error 1: init 2: set 3: bag (e.g., multi-set) 4: dictionary (e.g., associative array) Note that 0 and 1 represent error and initialization states, respectively. A set is an unordered collection of elements that MUST NOT have duplicates. A bag is an unordered collection of elements; it MAY have duplicates. A dictionary is a table that associates a key with a value. Sets have a number of important functions, including: o membership: returns TRUE if the element being tested is in the set, and FALSE otherwise o subset: returns TRUE if all elements in the first set are also in the second set o union: returns all elements from both sets with no duplicates o intersection: returns all elements that are in both sets with no duplicates o difference: returns all elements in the first set that are not in the second set Bags have a number of important functions in addition to the functions defined for sets (note that while the above set of functions for a set and a bag are the same, a bag is a different data type than a set): o multiplicity: returns the number of occurrences of an element in the bag Strassner, et al. Expires November 30, 2017 [Page 82]
Internet-Draft SUPA Generic Policy Model May 2017 o count: returns the number of all items, including duplicates o countDistinct: returns the number of items, where all duplicates are ignored A dictionary is an unordered set of key:value pairs, where each key is unique within a given dictionary. The combination of a key and a value is called an item. The format of an item is defined as one element (the key) followed by a colon followed by a second element (the value). Each item in a set of items is separated by a comma. Keys MUST NOT be NULL; values MAY be NULL. An example of a dictionary is {20:"FTP", 21:"FTP", 22: "SSH"}. An example of a null dictionary is simply {}. 5.13.4. SUPAPolicyCollection Relationships Currently, no relationships are defined for the SUPAGenericDecoratedComponent class (note that the decorator pattern obviates the need for relationships such as those in [6]). SUPAPolicyCollection participates in a single relationship, SUPAHasDecoratedPolicyComponent, as defined in section 5.7.3. 5.14. The Abstract Class "SUPAPolicyComponentDecorator" This is an optional class, and represents how the decorator pattern can be applied to objects that decorate another object. This is shown in Figure 25 below. A +--------------+---------------------+ | |/ | SUPAPolicyClauseComponentDecorator +------------+ | |\ | +----------+-------------------------+ 0..n | | SUPAHasDecoratedPolicyComponent | +---------------------------------+ ^ | | | C | | +---------------+---------------------+ | |SUPAHasDecoratedPolicyComponentDetail| / \ +---------------+---------------------+ A A \ / 0..1 +---------------+--------------+ | SUPAPolicyComponentDecorator | +------------------------------+ Figure 25. Decorating Objects that Decorate Another Object Strassner, et al. Expires November 30, 2017 [Page 83]
Internet-Draft SUPA Generic Policy Model May 2017 Figure 25 realizes a recursive decorator pattern, in that any concrete subclass of SUPAPolicyClauseComponentDecorator can be decorated by any concrete subclass of SUPAPolicyComponentDecorator. The SUPAHasPolicyClause aggregation enables one or more concrete subclasses of SUPAPolicyClauseComponentDecorator to wrap a concrete subclass of SUPAPolicyClause. Its semantics are defined by the SUPAPolicyClauseHasDecoratorDetail association class. 5.14.1. SUPAPolicyComponentDecorator Attributes Currently, there are two attributes defined for this class, which are described in the following subsections. Both attributes are used by subclasses to **constrain the behavior of that subclass**; they do **not** affect the relationship between the concrete subclass of SUPAPolicyComponentDecorator that is wrapping the concrete subclass of SUPAPolicyClauseComponentDecorator. This is different than the use of similar attributes defined in the SUPAHasDecoratedPolicyComponentDetail association class. The attributes of SUPAPolicyComponentDecorator are used to constrain the (concrete subclass of) the SUPAPolicyClauseComponentDecorator that is being wrapped. In contrast, the attributes of SUPAHasDecoratedPolicyComponentDetail are used to define which concrete subclasses of SUPAPolicyClauseComponentDecorator can be wrapped by which concrete subclasses of the SUPAPolicyComponentDecorator class. 5.14.1.1. The Attribute "supaPolCompConstraintEncoding" This is a mandatory non-negative enumerated integer that defines how to interpret each string in the supaPolCompConstraint class attribute. Values include: 0: error 1: init 2: OCL 2.4 3: OCL 2.x 4: OCL 1.x 5: QVT 1.2 - Relations Language 6: QVT 1.2 - Operational language 7: Alloy 8: ASCII Text Enumerations 0 and 1 signify an error state and an initialization state, respectively. Enumerations 2-4 are dedicated to OCL (with OCL 2.4 being the latest version as of this writing). QVT defines a set of languages [20] (the two most powerful and useful are defined by enumerations 5 and 6). Alloy is a language for describing constraints, and uses a SAT solver to guarantee correctness [21]. Enumeration 8 (ASCII Text) is not recommended (since it is informal, and hence, not verifiable), but is included for completeness. Strassner, et al. Expires November 30, 2017 [Page 84]
Internet-Draft SUPA Generic Policy Model May 2017 5.14.1.2. The Attribute "supaPolCompConstraint[0..n]" This is a mandatory array of string attributes. Each attribute specifies a constraint to be applied using the encoding defined in the supaPolCompConstraintEncoding class attribute. This provides a more rigorous and flexible treatment of constraints than is possible in [RFC3460], [4], [5], and [6]. Note: [0..n] means that this is a multi-valued property that may have zero or more attributes. 5.14.2. SUPAPolicyComponentDecorator Relationships A single relationship is currently defined for the SUPAPolicyComponentDecorator, which is described below. 5.14.2.1 The Aggregation "SUPAHasDecoratedPolicyComponent" This is a mandatory aggregation, and is part of a recursive decorator pattern. It is used to enable a concrete instance of a SUPAPolicyComponentDecorator to dynamically add behavior to a specific type (of concrete subclass) of a SUPAPolicyClauseComponentDecorator object. The semantics of this aggregation are defined by the SUPAHasDecoratedPolicyComponentDetail association class. 5.14.2.2. The Association Class "SUPAHasDecoratedPolicyComponentDetail" This is a mandatory concrete association class, and defines the semantics of the SUPAHasDecoratedPolicyComponent aggregation. The purpose of this class is to use the Decorator pattern to determine which concrete subclasses of the SUPAPolicyComponentDecorator class, if any, are required to augment the functionality of the concrete subclass of SUPAPolicyClauseComponentDecorator that is being used. Currently, there are two attributes defined for this class, which are described in the following subsections. Both attributes are used in this association class to constrain the **relationship** between the concrete subclass of SUPAPolicyComponentDecorator that is wrapping the concrete subclass of the SUPAPolicyClauseComponentDecorator class. 5.14.2.1.1. The Attribute "supaPolCompConstraintEncoding" This is a mandatory non-negative enumerated integer that defines how to interpret each string in the supaDecoratedConstraint class attribute. Values include: Strassner, et al. Expires November 30, 2017 [Page 85]
Internet-Draft SUPA Generic Policy Model May 2017 0: error 1: init 2: OCL 2.4 3: OCL 2.x 4: OCL 1.x 5: QVT 1.2 - Relations Language 6: QVT 1.2 - Operational language 7: Alloy 8: ASCII Text Enumerations 0 and 1 signify an error state and an initialization state, respectively. Enumerations 2-4 are dedicated to OCL (with OCL 2.4 being the latest version as of this writing). QVT defines a set of languages [20] (the two most powerful and useful are defined by enumerations 5 and 6). Alloy is a language for describing constraints, and uses a SAT solver to guarantee correctness [21]. Enumeration 8 (ASCII Text) is not recommended (since it is informal, and hence, not verifiable), but is included for completeness. If this class is instantiated, then this attribute SHOULD also be instantiated, and SHOULD be part of a conformant implementation. 5.14.2.1.2. The Attribute "supaPolCompConstraint[0..n]" This is a mandatory array of string attributes. Its purpose is to collect a set of constraints to be applied to a decorated object. The interpretation of each constraint in the array is defined in the supaDecoratedConstraintsEncoding class attribute. Note: [0..n] means that this is a multi-valued property that may have zero or more attributes. 5.15. The Concrete Class "SUPAPolicySource" This is an optional class that defines a set of managed entities that authored, or are otherwise responsible for, this SUPAPolicyRule. Note that a SUPAPolicySource does NOT evaluate or execute SUPAPolicies. Its primary use is for auditability and the implementation of deontic and/or alethic logic. A class diagram is shown in Figure 15. A SUPAPolicySource SHOULD be mapped to a role or set of roles (e.g., using the role-object pattern [11]). This enables role-based access control to be used to restrict which entities can author a given policy. Note that Role is a type of SUPAPolicyMetadata. 5.15.1. SUPAPolicySource Attributes Currently, no attributes are defined for this class. Strassner, et al. Expires November 30, 2017 [Page 86]
Internet-Draft SUPA Generic Policy Model May 2017 5.15.2. SUPAPolicySource Relationships SUPAPolicySource participates in a single relationship, SUPAHasPolicySource, as defined in section 5.3.2.1. SUPAPolicySource, and its subclasses, inherit the SUPAHasPolicyMetadata aggregation, which is defined in section 5.17.2.1. 5.16. The Concrete Class "SUPAPolicyTarget" This is an optional class that defines a set of managed entities that a SUPAPolicy is applied to. Figure 15 shows a class diagram of the SUPAPolicyTarget. A managed object must satisfy two conditions in order to be defined as a SUPAPolicyTarget. First, the set of managed entities that are to be affected by the SUPAPolicy must all agree to play the role of a SUPAPolicyTarget. In general, a managed entity may or may not be in a state that enables SUPAPolicies to be applied to it to change its state; hence, a negotiation process may need to occur to enable the SUPAPolicyTarget to signal when it is willing to have SUPAPolicies applied to it. Second, a SUPAPolicyTarget must be able to process (directly or with the aid of a proxy) SUPAPolicies. If a proposed SUPAPolicyTarget meets both of these conditions, it SHOULD set its supaPolicyTargetEnabled Boolean attribute to a value of TRUE. A SUPAPolicyTarget SHOULD be mapped to a role (e.g., using the role-object pattern). This enables role-based access control to be used to restrict which entities can author a given policy. Note that Role is a type of SUPAPolicyMetadata. 5.16.1. SUPAPolicyTarget Attributes Currently, no attributes are defined for the SUPAPolicyTarget class. 5.16.2. SUPAPolicyTarget Relationships SUPAPolicyTarget participates in a single relationship, SUPAHasPolicyTarget, as defined in section 5.3.2.3. It also inherits the SUPAHasPolicyMetadata aggregation (see section 5.17.2.1.). Strassner, et al. Expires November 30, 2017 [Page 87]
Internet-Draft SUPA Generic Policy Model May 2017 5.17. The Abstract Class "SUPAPolicyMetadata" Metadata is information that describes and/or prescribes characteristics and behavior of another object that is **not** an inherent, distinguishing characteristic or behavior of that object (otherwise, it would be an integral part of that object). For example, a socialSecurityNumber attribute should not be part of a generic Person class. First, most countries in the world do not know what a social security number is, much less use them. Second, a person is not created with a social security number; rather, a social security number is used to track people for administering social benefits, though it is also used as a form of identification. Continuing the example, a better way to add this capability to a model would be to have a generic Identification class, then define a SocialSecurityNumber subclass, populate it as necessary, and then define a composition between a Person and it (this is a composition because social security numbers are not reused). Since social security numbers are given to US citizens, permanent residents, and temporary working residents, and because it is also used to administer benefits, the composition is realized as an association class to define how it is being used. An example of descriptive metadata for network elements would be documentation about best current usage practices (this could also be in the form of a reference). An example of prescriptive metadata for network elements would be the definition of a time period during which specific types of operations are allowable. This is an optional class that defines the top of a hierarchy of model elements that are used to define different types of metadata that can be applied to policy and policy component objects. This enables common metadata to be defined as objects and then reused when the metadata are applicable. One way to control whether SUPAPolicyMetadata objects are reused is by using the attributes of the SUPAHasPolicyMetadataDetail association class. It is recommended that this class, along with its SUPAPolicyConcreteMetadata and SUPAPolicyMetadataDecorator subclasses, be used as part of a conformant implementation. It is defined to be optional, since metadata is not strictly required. However, metadata can help specify and describe SUPAPolicyObject entities, and can also be used to drive dynamic behavior. Strassner, et al. Expires November 30, 2017 [Page 88]
Internet-Draft SUPA Generic Policy Model May 2017 5.17.1. SUPAPolicyMetadata Attributes This section defines the attributes of the SUPAPolicyMetadata class. 5.17.1.1. The Attribute "supaPolMetadataDescription" This is an optional string attribute that defines a free-form textual description of this metadata object. 5.17.1.2. The Attribute "supaPolMetadataIDContent" This is a mandatory string attribute that represents part of the object identifier of an instance of this class. It defines the content of the object identifier. It works with another class attribute, called supaPolMetadataIDEncoding, which defines how to interpret this attribute. These two attributes form a tuple, and together enable a machine to understand the syntax and value of an object identifier for the object instance of this class. 5.17.1.3. The Attribute "supaPolMetadataIDEncoding" This is an optional non-zero enumerated integer attribute that represents part of the object identifier of an instance of this class. It defines the format of the object identifier. It works with another class attribute, called supaPolMetadataIDContent, which defines the content of the object ID. These two attributes form a tuple, and together enable a machine to understand the syntax and value of an object identifier for the object instance of this class. The supaPolMetadataIDEncoding attribute is mapped to the following values: 0: error (i.e., an error state) 1: init (i.e., an initialization state) 2: primary_key 3: foreign_key 4: GUID 5: UUID 6: URI 7: FQDN 8: FQPN 9: string_instance_id Note that 0 and 1 represent error and initialization states, respectively. Values 2-8 define the content as a reference. Value 9 defines the content as a string that is the canonical representation, in ASCII, of an instance ID of this object. Strassner, et al. Expires November 30, 2017 [Page 89]
Internet-Draft SUPA Generic Policy Model May 2017 5.17.1.4. The Attribute "supaPolMetadataName" This is an optional string attribute that defines the name of this SUPAPolicyMetadata object. 5.17.2. SUPAPolicyMetadata Relationships SUPAPolicyMetadata participates in two aggregations. The first, SUPAHasPolicyMetadata, which is defined in the following subsection. The second, SUPAHasMetadataDecorator, is defined in section 5.19.2. 5.17.2.1. The Aggregation "SUPAHasPolicyMetadata" This is a mandatory aggregation that defines the set of SUPAPolicyMetadata that are aggregated by this particular SUPAPolicyObject. The multiplicity of this relationship is defined as 0..n on the aggregate (SUPAPolicyObject) side, and 0..n on the part (SUPAPolicyMetadata) side. This means that this relationship is optional. However, it is recommended that this aggregation be used as part of a conformant implementation, because it enables metadata to be attached to all objects that inherit from the SUPAPolicyObject class. The semantics of this aggregation are implemented using the SUPAHasPolicyMetadataDetail association class. 5.17.2.2. The Abstract Class "SUPAHasPolicyMetadataDetail" This is a mandatory concrete association class, and defines the semantics of the SUPAHasPolicyMetadata aggregation. Its purpose is to determine which SUPAPolicyMetadata object instances should be attached to which particular object instances of the SUPAPolicyObject class. This is done by using the attributes and relationships of the SUPAPolicyMetadataDetail class to constrain which SUPAPolicyMetadata objects can be aggregated by which particular SUPAPolicyObject instances. 5.17.2.2.1. The Attribute "supaPolMetadataConstraintEncoding" This is an optional non-negative enumerated integer that defines how to interpret each string in the supaPolMetadataConstraint class attribute. Values include: 0: error 1: init 2: OCL 2.4 3: OCL 2.x 4: OCL 1.x 5: QVT 1.2 - Relations Language 6: QVT 1.2 - Operational language 7: Alloy 8: ASCII Text Strassner, et al. Expires November 30, 2017 [Page 90]
Internet-Draft SUPA Generic Policy Model May 2017 Enumerations 0 and 1 signify an error state and an initialization state, respectively. Enumerations 2-4 are dedicated to OCL (with OCL 2.4 being the latest version as of this writing). QVT defines a set of languages [20] (the two most powerful and useful are defined by enumerations 5 and 6). Alloy is a language for describing constraints, and uses a SAT solver to guarantee correctness [21]. Enumeration 8 (ASCII Text) is not recommended (since it is informal, and hence, not verifiable), but is included for completeness. If this class is instantiated, then this attribute SHOULD also be instantiated, and SHOULD be part of a conformant implementation. 5.17.2.2.2. The Attribute "supaPolMetadataConstraint[0..n]" This is an optional array of string attributes. Each attribute specifies a constraint to be applied using the format identified by the value of the supaPolMetadataPolicyConstraintEncoding class attribute. This provides a more rigorous and flexible treatment of constraints than is possible in [RFC3460]. If this class is instantiated, then this attribute SHOULD also be instantiated, and should be part of a conformant implementation. Note: [0..n] means that this is a multi-valued property that has zero or more attributes. 5.17.2.2.3. The Attribute "supaPolMetadataIsApplicable" This is an optional Boolean attribute. If the value of this attribute is TRUE, then the SUPAPolicyMetadata object(s) of this particular SUPAHasPolicyMetadata aggregation SHOULD be aggregated by this particular SUPAPolicyObject. 5.18. The Concrete Class "SUPAPolicyConcreteMetadata" This is an optional concrete class. It defines an object that will be wrapped by concrete instances of the SUPAPolicyMetadataDecorator class. It can be viewed as a "carrier" for metadata that will be attached to a subclass of SUPAPolicyObject. Since the decorator pattern is used, any number of concrete subclasses of the SUPAPolicyMetadataDecorator class can wrap an instance of the SUPAPolicyConcreteMetadata class. It is recommended that this class be used as part of a conformant implementation. 5.18.1. SUPAPolicyConcreteMetadata Attributes Currently, two attributes are defined for the SUPAPolicyConcreteMetadata class, and are described in the following subsections. Strassner, et al. Expires November 30, 2017 [Page 91]
Internet-Draft SUPA Generic Policy Model May 2017 5.18.1.1. The Attribute "supaPolMDValidPeriodEnd" This is an optional attribute. Its data type should be able to express a date and a time. This attribute defines the ending date and time that this Metadata object is valid for. 5.18.1.2. The Attribute "supaPolMDValidPeriodStart" This is an optional attribute. Its data type should be able to express a date and a time. This attribute defines the starting date and time that this Metadata object is valid for. 5.18.2. SUPAPolicyConcreteMetadata Relationships This class inherits the relationships of the SUPAPolicyMetadata class; see section 5.17.2. It can also be used by subclasses of the SUPAPolicyMetadataDecorator class, and hence, can participate in the SUPAHasMetadataDecorator aggregation; see section 5.19.2. 5.19. The Abstract Class "SUPAPolicyMetadataDecorator" This is an optional class, and is used to implement the decorator pattern (see section 4.2.1.2.) for metadata objects. This pattern enables all or part of one or more SUPAPolicyMetadataDecorator subclasses to "wrap" a SUPAPolicyConcreteMetadata object instance. It is recommended that this class be used as part of a conformant implementation. 5.19.1. SUPAPolicyMetadataDecorator Attributes Currently, no attributes are defined for this class. 5.19.2. SUPAPolicyMetadataDecorator Relationships This class inherits the relationships of the SUPAPolicyMetadata class; see section 5.17.2. It also defines a single aggregation, SUPAHasMetadataDecorator, which is used to implement the decorator pattern, as described in the following subsections. 5.19.2.1. The Aggregation "SUPAHasMetadataDecorator" This is an optional aggregation, and is part of a decorator pattern. It is used to enable a concrete instance of a SUPAPolicyMetadataDecorator to dynamically add behavior to a SUPAPolicyConcreteMetadata object instance. The semantics of this aggregation are defined by the SUPAHasMetadataDecoratorDetail association class. It is recommended that this aggregation be part of a conformant implementation. Strassner, et al. Expires November 30, 2017 [Page 92]
Internet-Draft SUPA Generic Policy Model May 2017 The multiplicity of this aggregation is 0..1 on the aggregate (SUPAPolicyMetadataDecorator) side and 1..n on the part (SUPAPolicyMetadata) side. This means that if this aggregation is defined, then at least one SUPAPolicyMetadata object (e.g., a concrete subclass of SUPAPolicyMetadataDecorator) must also be instantiated and wrapped by this SUPAPolicyConcreteMetadata object instance. The semantics of this aggregation are defined by the SUPAHasMetadataDecoratorDetail association class. 5.19.2.2. The Association Class "SUPAHasMetadataDecoratorDetail" This is an optional concrete association class, and defines the semantics of the SUPAHasMetadataDecorator aggregation. The purpose of this class is to use the Decorator pattern to determine which SUPAPolicyMetadataDecorator object instances, if any, are required to augment the functionality of the SUPAPolicyConcreteMetadata object instance that is being used. Three attributes are defined for this class, which are described in the following subsections. It is recommended that this association class be part of a conformant implementation. 5.19.2.2.1. The Attribute "supaPolMetadataDecConstraintEncoding" This is an optional non-negative enumerated integer that defines how to interpret each string in the supaPolMetadataDecConstraint class attribute. Values include: 0: error 1: init 2: OCL 2.4 3: OCL 2.x 4: OCL 1.x 5: QVT 1.2 - Relations Language 6: QVT 1.2 - Operational language 7: Alloy 8: ASCII Text Enumerations 0 and 1 signify an error state and an initialization state, respectively. Enumerations 2-4 are dedicated to OCL (with OCL 2.4 being the latest version as of this writing). QVT defines a set of languages [20] (the two most powerful and useful are defined by enumerations 5 and 6). Alloy is a language for describing constraints, and uses a SAT solver to guarantee correctness [21]. Enumeration 8 (ASCII Text) is not recommended (since it is informal, and hence, not verifiable), but is included for completeness. If this class is instantiated, then this attribute SHOULD also be instantiated, and SHOULD be part of a conformant implementation. Strassner, et al. Expires November 30, 2017 [Page 93]
Internet-Draft SUPA Generic Policy Model May 2017 5.19.2.2.2. The Attribute "supaPolMetadataDecConstraint[0..n]" This is an optional array of string attributes. Each attribute specifies a constraint to be applied using the format identified by the value of the supaPolMetadataDecConstraintEncoding class attribute. This provides a more rigorous and flexible treatment of constraints than is possible in [RFC3460]. If this class is instantiated, then this attribute SHOULD also be instantiated, and should be part of a conformant implementation. Note: [0..n] means that this is a multi-valued property that has zero or more attributes. 5.19.2.2.3. The Attribute "supaPolMetadataDecIsApplicable" This is an optional Boolean attribute. If the value of this attribute is TRUE, then the SUPAPolicyMetadataDecorator object(s) of this particular SUPAHasMetadataDecorator aggregation SHOULD be aggregated by this particular SUPAPolicyConcreteMetadata object. 5.20. The Concrete Class "SUPAPolicyAccessMetadataDef" This is an optional concrete class that defines access control information, in the form of metadata, that can be added to a SUPAPolicyObject. This is done using the SUPAHasPolicyMetadata aggregation (see section 5.2.2.). This enables all or part of a standardized description and/or specification of access control for a given SUPAPolicyObject to be easily changed at runtime by wrapping an object instance of the SUPAPolicyConcreteMetadata class (or its subclass) with all or part of this object, and then adorning the SUPAPolicyObject with the SUPAPolicyConcreteMetadata object instance. 5.20.1. SUPAPolicyAccessMetadataDef Attributes Currently, the SUPAPolicyAccessMetadataDef class defines three attributes; these are described in the following subsections. 5.20.1.1. The Attribute "supaPolAccessPrivilegeDef" This is an optional non-negative enumerated integer attribute. It specifies the access privileges that external Applications have when interacting with a specific SUPAPolicyObject that is adorned with an instance of this SUPAPolicyAccessMetadataDef object. This enables the management system to control, in a consistent manner, the set of operations that external Applications have for SUPAPolicies and components of SUPAPolicies. Values include: Strassner, et al. Expires November 30, 2017 [Page 94]
Internet-Draft SUPA Generic Policy Model May 2017 0: error 1: init 2: read only (for all policy components) 3: read and write (for all policy components) 4: privileges are specified by an external MAC model 5: privileges are specified by an external DAC model 6: privileges are specified by an external RBAC model 7: privileges are specified by an external ABAC model 8: privileges are specified by an external custom model Note that 0 and 1 represent error and initialization states, respectively. Values 4-8 indicate that a formal external access control model is used. The name of this model, and its location, are specified in two other class attributes, called supaPolAccessPrivilegeModelName and supaPolAccessPrivilegeModelRef. MAC, DAC, RBAC, and ABAC (values 4-7 stand for Mandatory Access Control, Discretionary Access Control, Role-Based Access Control, and Attribute-Based Access Control, respectively. They are defined in [13]. A value of 8 indicates that a formal external model that is not MAC, DAC, RBAC, or ABAC is used. 5.20.1.2. The Attribute "supaPolAccessPrivilegeModelName" This is an optional string attribute that contains the name of the access control model being used. If the value of the supaPolAccessPrivilegeDef is 0-2, then the value of this attribute is not applicable. Otherwise, the text in this class attribute should be interpreted according to the value of the supaPolAccessPrivilegeModelRef class attribute. 5.20.1.3. The Attribute "supaPolAccessPrivilegeModelRef" This is an optional non-negative enumerated integer attribute that defines the data type of the supaPolAccessPrivilegeModelName attribute. If the value of the supaPolAccessPrivilegeDef class attribute is 0-2, then the value of this attribute is not applicable. Otherwise, the value of this class attribute defines how to interpret the text in the supaPolAccessPrivilegeModelRef class attribute. Values include: 0: error 1: init 2: GUID 3: UUID 4: URI 5: FQDN 6: FQPN 7: string_instance_id Strassner, et al. Expires November 30, 2017 [Page 95]
Internet-Draft SUPA Generic Policy Model May 2017 Note that 0 and 1 represent error and initialization states, respectively. Values 2-6 define the content as a reference. Value 7 defines the content as a string that is the canonical representation, in ASCII, of an instance ID of this object. 5.21. The Concrete Class "SUPAPolicyVersionMetadataDef" This is an optional concrete class that defines versioning information, in the form of metadata, that can be added to a SUPAPolicyObject. This enables all or part of a standardized description and/or specification of version information for a given SUPAPolicyObject to be easily changed at runtime by wrapping an object instance of the SUPAPolicyConcreteMetadata class (or its subclass) with all or part of this object. 5.21.1. SUPAPolicyVersionMetadataDef Attributes Version information is defined in a generic format based on the Semantic Versioning Specification [18] as follows: <major>.<minor>.<patch>[<pre-release>][<build-metadata>] where the first three components (major, minor, and patch) MUST be present, and the latter two components (pre-release and build- metadata) MAY be present. A version number MUST take the form <major>.<minor>.<patch>, where <major>, <minor>, and <patch> are each non-negative integers that MUST NOT contain leading zeros. In addition, the value of each of these three elements MUST increase numerically. In this approach: o supaVersionMajor denotes a new release; this number MUST be incremented when either changes are introduced that are not backwards-compatible, and/or new functionality not previously present is introduced o supaVersionMinor denotes a minor release; this number MUST be incremented when new features and/or bug fixes to a major release that are backwards-compatible are introduced, and/or if any features are marked as deprecated o supaVersionPatch denotes a version that consists ONLY of bug fixes, and MUST be incremented when these bug fixes are Not backwards-compatible When multiple versions exist, the following rules define their precedence: 1. Precedence MUST be calculated by separating the version into major, minor, patch, and pre-release identifiers, in that order. Note that build-metadata is NOT used to calculated precedence. Strassner, et al. Expires November 30, 2017 [Page 96]
Internet-Draft SUPA Generic Policy Model May 2017 2. Precedence is determined by the first difference when comparing each of these identifiers, from left to right, as follows: a. Major, minor, and patch versions are always compared numerically (e.g., 1.0.0 < 2.0.0 < 2.1.0 < 2.1.1) b. When major, minor, and patch are equal, a pre-release version has LOWER precedence than a normal version (e.g., 1.0.0-alpha < 1.0.0) c. Precedence for two pre-release versions with the same major, minor, and patch version MUST be determined by comparing each dot separated identifier from left to right until a difference is found as follows: - identifiers consisting only of digits are compared numerically and identifiers with letters and/or hyphens are compared lexically in ASCII sort order - Numeric identifiers always have lower precedence than non-numeric identifiers - A larger set of pre-release fields has a higher precedence than a smaller set, if all of the preceding identifiers are equal 3. Example: 1.0.0-alpha < 1.0.0-alpha.1 < 1.0.0-alpha-beta < 1.0.0-beta < 1.0.0-beta.2 < 1.0.0-rc.1 < 1.0.0. Currently, the SUPAPolicyVersionMetadataDef class defines five attributes; these are described in the following subsections. 5.21.1.1. The Attribute "supaVersionMajor" This is a mandatory string attribute, and contains a string representation of an integer that is greater than or equal to zero. It indicates that a significant increase in functionality is present in this version. It MAY also indicate that this version has changes that are NOT backwards-compatible; this MAY be denoted in the supaVersionBuildMetadata class attribute. The special string "0.1.0" is for initial development that MUST NOT be considered stable. Improvements to this initial version, before they are released to the public, are denoted by incrementing the minor and patch version numbers. The major version X (i.e., X.y.z, where X > 0) MUST be incremented if any backwards incompatible changes are introduced. It MAY include minor and patch level changes. The minor and patch version numbers MUST be reset to 0 when the major version number is incremented. Strassner, et al. Expires November 30, 2017 [Page 97]
Internet-Draft SUPA Generic Policy Model May 2017 5.21.1.2. The Attribute "supaVersionMinor" This is a mandatory string attribute, and contains a string representation of an integer that is greater than or equal to zero. It indicates that this release contains a set of features and/or bug fixes that MUST be backwards-compatible. The minor version Y (i.e., x.Y.z, where x > 0) MUST be incremented if new, backwards-compatible changes are introduced. It MUST be incremented if any features are marked as deprecated. It MAY be incremented if new functionality or improvements are introduced. It MAY include patch level changes. The patch version number MUST be reset to 0 when the minor version number is incremented. 5.21.1.3. The Attribute "supaVersionPatch" This is a mandatory string attribute, and contains a string representation of an integer that is greater than or equal to zero. It indicates that this version contains ONLY bug fixes. The patch version Z (i.e., x.y.Z, where x > 0) MUST be incremented if new, backwards-compatible changes are introduced. A bug fix is defined as an internal change that fixes incorrect behavior. 5.21.1.4. The Attribute "supaVersionPreRelease" This is an optional string attribute, and contains a string defining the pre-release version. A pre-release version MAY be denoted by appending a hyphen and a series of dot-separated identifiers immediately following the patch version. Identifiers MUST comprise only ASCII alphanumerics and a hyphen. Identifiers MUST NOT be empty. Numeric identifiers MUST NOT include leading zeroes. Pre-release versions have a lower precedence than the associated normal version. A pre-release version indicates that the version is unstable and might not satisfy the intended compatibility requirements as denoted by its associated normal version. Examples include: 1.0.0-alpha, 1.0.0-alpha.1, 1.0.0-0.3.7, and 1.0.0-x.7.z.92. 5.21.1.5. The Attribute "supaVersionBuildMetadata" This is an optional string attribute, and contains a string defining the build metadata. Build metadata MAY be denoted by appending a plus sign and a series of dot-separated identifiers immediately following the patch or pre-release version. Identifiers MUST be made up of only ASCII alphanumerics and a hyphen. Identifiers MUST NOT be empty. Build metadata SHOULD be ignored when determining version precedence. Examples include: 1.0.0.-alpha+1, 1.0.0+20130313144700, and 1.0.0-beta+exp.sha.5114f85. Strassner, et al. Expires November 30, 2017 [Page 98]
Internet-Draft SUPA Generic Policy Model May 2017 6. SUPA ECAPolicyRule Information Model This section defines the classes, attributes, and relationships of the SUPA ECAPolicyRule Information Model (EPRIM). Unless otherwise stated, all classes (and attributes) defined in this section were abstracted from DEN-ng [2], and a version of them are in the process of being added to [5]. 6.1. Overview Conceptually, the EPRIM is a set of subclasses that specialize the concepts defined in the GPIM for representing the components of a Policy that uses ECA semantics. This is shown in Figure 26 (only new EPRIM subclasses and their GPIM superclasses are shown; note that the SUPAPolicyMetadata hierarchy is used **as is**). (Class of another model that SUPA is integrating into) | +---SUPAPolicyObject (5.2) | +---SUPAPolicyStructure (5.3) | | | +---SUPAECAPolicyRule (6.4) | | | +---SUPAECAPolicyRuleAtomic (6.5) | | | +---SUPAECAPolicyRuleComposite (6.6) | +---SUPAPolicyComponentStructure (5.4) | +---SUPAPolicyClause (5.5) | | | +---SUPABooleanClause (6.7) | | | +---SUPABooleanClauseAtomic (6.8) | | | +---SUPABooleanClauseComposite (6.9) | +---SUPAPolicyClauseComponentDecorator (5.7) | +---SUPAECAComponent(6.10) | +---SUPAPolicyEvent (6.11) | +---SUPAPolicyCondition (6.12) | +---SUPAPolicyAction (6.13) Figure 26. The EPRIM Class Hierarchy Strassner, et al. Expires November 30, 2017 [Page 99]
Internet-Draft SUPA Generic Policy Model May 2017 Specifically, the EPRIM specializes the SUPAPolicyStructure class class to create a SUPAECAPolicyRule (see sections 6.4 - 6.6); it also specializes two subclasses of the SUPAPolicyComponentStructure class to create two new sets of policy components. These two SUPAPolicyComponentStructure subclasses are: o a new subclass of SUPAPolicyClause, called SUPABooleanClause (see sections 6.7 - 6.9), is defined for constructing Boolean clauses that are specific to the needs of ECA Policy Rules o a new subclass of SUPAPolicyClauseComponentDecorator, called SUPAECAComponent (see sections 6.10 - 6.13), is defined for constructing reusable objects that represent Events, Conditions, and Actions The EPRIM provides new functionality, based on the GPIM, by extending the GPIM to define new classes and relationships. The EPRIM does NOT define new classes that are not inherited from existing GPIM classes. This ensures that the semantics of the GPIM are not changed, even though new functionality (for ECA Policy Rules and components) are being defined. The overall strategy for refining the GPIM is as follows: o SUPAECAPolicyRule is defined as a subclass of the GPIM SUPAPolicyStructure class o A SUPAECAPolicyRule has event, condition, and action clauses o Conceptually, this can be viewed as three aggregations between the SUPAECAPolicyRule and each clause o Each aggregation uses an instance of a concrete subclass of SUPAPolicyClause; this can be a SUPABooleanClause (making it ECA-specific), a SUPAEncodedClause (making it generic in nature), or a new subclass of SUPAPolicyClause o Concrete subclasses of SUPAPolicyClause may be decorated with zero or more concrete subclasses of the SUPAPolicyComponentDecorator class o An optional set of GPIM SUPAPolicySource objects can be defined to represent the authoring of a SUPAECAPolicyRule o An optional set of GPIM SUPAPolicyTarget objects can be defined to represent the set of managed entities that will be affected by this SUPAECAPolicyRule o An optional set of SUPAPolicyMetadata can be defined for any of the objects that make up a SUPAECAPolicyRule, including any of its components Strassner, et al. Expires November 30, 2017 [Page 100]
Internet-Draft SUPA Generic Policy Model May 2017 6.2. Constructing a SUPAECAPolicyRule There are several different ways to construct a SUPAECAPolicyRule; they differ in which set of components are used to define the content of the SUPAECAPolicyRule, and whether each component is decorated or not. The following are some examples of creating a SUPAECAPolicyRule: o Define three types of SUPABooleanClauses, one each for the event, condition, and action clauses that make up a SUPAECAPolicyRule, and then o For one or more of the above clauses, associate an appropriate set of SUPAPolicyEvent, SUPAPolicyCondition, or SUPAPolicyAction objects, and complete the clause using an appropriate SUPAPolicyOperator and a corresponding SUPAPolicyValue or SUPAPolicyVariable (e.g., resulting in the phrase "SUPAPolicyAction = SUPAPolicyEvent") o Define a SUPAPolicyCollection component, which is used to aggregate a set of objects appropriate for a clause, and complete the clause using an appropriate SUPAPolicyOperator and a corresponding SUPAPolicyValue or SUPAPolicyVariable o Create a new concrete subclass of SUPAPolicyClauseComponentDecorator (i.e., a sibling class of SUPAECAComponent) that can wrap concrete instances of SUPAPolicyClause (i.e., SUPABooleanClause); note that this approach enables the new concrete subclass of SUPAPolicyClauseComponentDecorator to optionally be decorated as well o Create a new concrete subclass of SUPAPolicyStructure that provides ECA-specific functionality, and define all or part of its content by aggregating a set of SUPAPolicyClauses Note that compound Boolean clauses may be formed using one or more SUPABooleanClauseComposite objects with one or more SUPABooleanClauseAtomic objects. 6.3. Working With SUPAECAPolicyRules A SUPAECAPolicyRule is a type of SUPAPolicy. It is a tuple that MUST have three clauses, defined as follows: o The event clause defines a Boolean expression that, if TRUE, triggers the evaluation of its condition clause (if the event clause is not TRUE, then no further action for this policy rule takes place). o The condition clause defines a Boolean expression that, if TRUE, enables the actions in the action clause to be executed (if the condition clause is not TRUE, then no further action for this policy rule takes place). Strassner, et al. Expires November 30, 2017 [Page 101]
Internet-Draft SUPA Generic Policy Model May 2017 o The action clause contains a set of actions that MAY be executed; which particular actions are executed are defined by metadata and the supaECAEvalStrategy attribute (see section 6.6.1.1.). Each of the above clauses can be a simple Boolean expression (of the form {variable operator value}, or a compound Boolean expression consisting of Boolean combinations of clauses. Compound Boolean expressions SHOULD be in CNF or DNF. Note that each of the above three clauses MAY have a set of SUPAPolicyMetadata objects that can constrain, or otherwise affect, how that clause is treated. For example, a set of SUPAPolicyMetadata MAY affect whether none, some, or all actions are executed, and what happens if an action fails. Each of the three clauses can be constructed from either a SUPAEncodedClause or a SUPABooleanClause. The advantage of using SUPAEncodedClauses is simplicity, as the content of the clause is encoded directly into the attributes of the SUPAEncodedClause. The advantage of using SUPABooleanClauses is reusability, since each term in each clause is potentially a reusable object. Since a SUPABooleanClause is a subclass of a SUPAPolicyClause (see Section 6.7), it can be decorated by one or more concrete subclasses of SUPAPolicyClauseComponentDecorator. Therefore, a SUPAECAPolicyRule can be built entirely from objects defined in the GPIM and EPRIM, which facilitates the construction of SUPAPolicies by a machine. The relation between a SUPAECAPolicyRule and a SUPAPolicyClause is shown in Figure 27, and is further explained in Section 6.4. A A +---------------------+ +------------------+ | |/ \ SUPAHasPolicyClause \| | | SUPAPolicyStructure | A ---------+------------+ SUPAPolicyClause | | |\ / ^ /| | +---------+-----------+ 0..n | 1..n +--------+---------+ / \ | / \ I | I A I | A I +-------+-----------+ | +--------+----------+ | SUPAECAPolicyRule | | | SUPABooleanClause | +-------------------+ | +-------------------+ | A | +---------------+-----------+ | SUPAHasPolicyClauseDetail | +---------------------------+ Figure 27. SUPAECAPolicyRule Clauses Strassner, et al. Expires November 30, 2017 [Page 102]
Internet-Draft SUPA Generic Policy Model May 2017 The SUPAHasPolicyClause aggregation is implemented using the SUPAHasPolicyClauseDetail association class. These were described in sections 5.3.2.7 and 5.3.2.8, respectively. 6.4. The Abstract Class "SUPAECAPolicyRule" This is a mandatory abstract class, which is a PolicyContainer that aggregates PolicyEvents, PolicyConditions, PolicyActions into a type of policy rule known as an Event-Condition-Action (ECA) policy rule. As previously explained, this has the following semantics: IF the event clause evaluates to TRUE IF the condition clause evaluates to TRUE THEN execute actions in the action clause ENDIF ENDIF The event clause, condition clause, and action clause collectively form a three-tuple. Each clause MUST be defined by at least one SUPAPolicyClause (which MAY be decorated with other elements, using concrete subclasses of the SUPAPolicyClauseComponentDecorator class, as described in section 5.7). Each of the three types of clauses is a 3-tuple of the form: {variable operator value} Each of the three clauses MAY be combined with additional clauses using any combination of logical AND, OR, and NOT operators; this forms a "compound" Boolean clause. For example, if A, B, and C are three attributes in an event, then a valid event clause could be: (A AND B) OR C Note that the above expression is in DNF; the equivalent CNF form is ((A OR C) AND (B OR C)). In either case, the output of all three clauses is either TRUE or FALSE; this facilitates combining and chaining SUPAECAPolicyRules. An action clause MAY invoke a SUPAPolicyAction from the same or a different SUPAECAPolicyRule. However, a SUPAPolicy MUST NOT be called directly by a SUPAECAPolicyRule action clause; this is because the semantics of a SUPAECAPolcyRule dictate that some type of event triggers its evaluation (among other reasons). Strassner, et al. Expires November 30, 2017 [Page 103]
Internet-Draft SUPA Generic Policy Model May 2017 An ECAPolicyRule MAY be optionally augmented with SUPAPolicySource and/or SUPAPolicyTarget objects (see sections 5.15 and 5.16, respectively). All objects that make up a SUPAECAPolicyRule MAY have SUPAPolicyMetadata objects (see section 5.17) attached to them to further describe and/or specify behavior. When defined in an information model, each of the event, condition, and action clauses MUST be represented as an aggregation between a SUPAECAPolicyRule (the aggregate) and a set of event, condition, or action objects (the components). However, a data model MAY map these definitions to a more efficient form (e.g., by flattening these three types of object instances, along with their respective aggregations, into a single object instance). The composite pattern [3] is applied to the SUPAECAPolicyRule class, enabling its (concrete) subclasses to be used as either a stand-alone policy rule or as a hierarchy of policy rules. SUPAECAPolicyRuleComposite and SUPAECAPolicyRuleAtomic both inherit from SUPAECAPolicyRule. This means that they are both a type of SUPAECAPolicyRule. Hence, the HasSUPAECAPolicyRule aggregation enables a particular SUPAECAPolicyRuleComposite object to aggregate both SUPAECAPolicyRuleComposite as well as SUPAECAPolicyRuleAtomic objects. In contrast, a SUPAECAPolicyRuleAtomic can NOT aggregate either a SUPAECAPolicyRuleComposite or a SUPAECAPolicyRuleAtomic. SUPAECAPolicyRuleAtomic and SUPAECAPolicyRuleComposite are defined in sections 6.5 and 6.6, respectively. This is shown in Figure 28. A 1..n +-------------------+ \| | +--------------- + SUPAECAPolicyRule | | /| | | +--------+----------+ | / \ | SUPAHasECAPolicyRule I | I | I | I | +---------------+-------------+ | I I / \ I I A I I C \ / 0..1 I C I +-----+---------+----------+ +-----------+-----------+ |SUPAECAPolicyRuleComposite| |SUPAECAPolicyRuleAtomic| +--------------------------+ +-----------------------+ Figure 28. The Composite Pattern Applied to a SUPAECAPolicyRule Strassner, et al. Expires November 30, 2017 [Page 104]
Internet-Draft SUPA Generic Policy Model May 2017 Note that the HasSUPAECAPolicyRule aggregation is defined by the HasSUPAECAPolicyRuleDetail association class; both are defined in sections 6.6.2 and 6.6.3, respectively. 6.4.1. SUPAECAPolicyRule Attributes Currently, the SUPAECAPolicyRule defines two attributes, as described in the following subsections. 6.4.1.1. The Attribute "supaECAPolicyRulePriority" This is a mandatory non-negative integer attribute that defines the priority of this particular SUPAECAPolicyRule. A larger value indicates a higher priority. A default value of 0 MAY be assigned. Priority is used primarily for 2 reasons: (1) to resolve conflicts among policy actions (e.g., given a set of conflicting actions, which one will execute) and (2) to define the execution order of policy actions (e.g., when one action may depend on the output of one or more previous actions). 6.4.1.2. The Attribute "supaECAPolicyRuleStatus" This is an optional non-negative enumerated integer whose value defines the current status of this policy rule. Values include: 0: error 1: init 2: In development, not ready to be deployed 1: Ready to be deployed 2: Deployed but not enabled 3: Deployed and enabled, but not executed 4: Executed without errors 5: Executed with errors 6: Aborted during execution Note that 0 and 1 represent error and initialization states, respectively. 6.4.2. SUPAECAPolicyRule Relationships Currently, the SUPAECAPolicyRule does not define any relationships. It inherits all four relationships defined by the SUPAPolicyStructure class (see section 5.3.2.). 6.5. The Concrete Class "SUPAECAPolicyRuleAtomic" This is a mandatory concrete class. This class is a type of PolicyContainer, and represents a SUPAECAPolicyRule that can operate as a single, stand-alone, manageable object. Strassner, et al. Expires November 30, 2017 [Page 105]
Internet-Draft SUPA Generic Policy Model May 2017 Put another way, a SUPAECAPolicyRuleAtomic object can NOT be modeled as a set of hierarchical SUPAECAPolicyRule objects; if this is required, then a SUPAECAPolicyRuleComposite object should be used instead. 6.5.1. SUPAECAPolicyRuleAtomic Attributes Currently, the SUPAECAPolicyRuleAtomic class defines a single attribute, as described in the following subsection. 6.5.1.1. The Attribute "supaECAPolActionEvalStrategy" This is a mandatory, non-zero, integer attribute that enumerates a set of allowable alternatives that define how the set of SUPAPolicyAction object instances in a SUPAECAPolicyRuleAtomic object instance are evaluated. It is assumed that the event and condition clauses of this SUPAECAPolicyRule have evaluated to TRUE. This attribute controls which SUPAPolicyActions are executed for a given SUPAPolicyRuleAtomic object instance when it contains multiple SUPAPolicyActions. Values include: 0: error 1: init 2: execute the first SUPAPolicyAction in the SUPAPolicyRuleAtomic object and then terminate 3: execute the last SUPAPolicyAction in the SUPAPolicyRuleAtomic object and then terminate 4: execute only the highest priority SUPAPolicyAction(s) in the SUPAPolicyRuleAtomic object and then terminate 5: execute all SUPAPolicyActions in prioritized order (if any) regardless of whether other SUPAPolicyActions succeed or fail 6: execute all SUPAPolicyActions in prioritized order (if any) until at least one SUPAPolicyAction fails, and then terminate Note that 0 and 1 represent error and initialization states, respectively. Values 2 and 3 MUST execute a single SUPAPolicyAction, and then terminate execution of the SUPAECAPolicyRuleAtomic object. If the value of supaECAPolActionEvalStrategy is 4, 5 or 6, then all SUPAPolicyActions that have a priority will be executed first, starting with the SUPAPolicyAction(s) that have the highest priority, and then descending in prioritized order. During this process, any SUPAPolicyActions that have the SAME priority MAY be executed in any order. After all SUPAPolicyActions that have an associated priority have executed, then all SUPAPolicyAction(s) that do not have a priority are then executed (in any order). Assume that the actions in a given SUPAPolicyAction are defined as follows: Strassner, et al. Expires November 30, 2017 [Page 106]
Internet-Draft SUPA Generic Policy Model May 2017 SUPAPolicyAction A, priority 0 SUPAPolicyAction B, priority 10 SUPAPolicyAction C, priority 5 SUPAPolicyAction D, no priority SUPAPolicyAction E, no priority Then, if the supaECAPolActionEvalStrategy attribute value equals: 0: an error is issued 1: this SUPAPolicyAction MUST NOT be used (since it is not yet properly initialized) 2: only SUPAPolicyAction A is executed 3: only SUPAPolicyAction E is executed 4: only SUPAPolicyAction B is executed 5: all SUPAPolicyActions are executed, regardless of any failures; the order of execution is B, then C, then A, then one of either D or E, then the other of D or E 6: all SUPAPolicyActions are executed until a failure is detected, and then execution for all SUPAPolicyActions terminate; the execution order (up to the occurrence of the failure) is B, then C, then A, then one of either D or E, then the other of D or E 6.5.2. SUPAECAPolicyRuleAtomic Relationships Currently, the SUPAECAPolicyRuleAtomic class does not define any relationships. 6.6. The Concrete Class "SUPAECAPolicyRuleComposite" This is a mandatory concrete class. This class is a type of PolicyContainer, and represents a SUPAECAPolicyRule as a hierarchy of SUPAPolicy objects, where the hierarchy contains instances of a SUPAECAPolicyRuleAtomic and/or SUPAECAPolicyRuleComposite objects. Each of the SUPAPolicy objects, including the outermost SUPAECAPolicyRuleComposite object, are separately manageable. More importantly, each SUPAECAPolicyRuleComposite object represents an aggregated object that is itself manageable. The difference between a SUPAECAPolicyRuleComposite and ability SUPAECAPolicyRuleAtomic is that each SUPAECAPolicyRuleComposite defines its own scope. This means that all instances of the SUPAECAPolicyRuleAtomic and SUPAECAPolicyRuleComposite classes will execute according to their priorities. This means that the priority of the SUPAECAPolicyRuleComposite object is used to determine the position that its containing SUPAPolicyActions will be executed; the priorities of the contained SUPAPolicyActions are then used. Consider the following example: Strassner, et al. Expires November 30, 2017 [Page 107]
Internet-Draft SUPA Generic Policy Model May 2017 +--A (SUPAECAPolicyRuleAtomic), priority 5 | +--B (SUPAECAPolicyRuleAtomic), priority 0 | +--C (SUPAECAPolicyRuleComposite), priority 10 | | | +--C1 (SUPAECAPolicyRuleAtomic), priority 2 | | | +--C2 (SUPAECAPolicyRuleAtomic), priority 1 | +--D (SUPAECAPolicyRuleAtomic), no priority The execution order will be C1, followed by C2, followed by A, followed by B, followed by D. 6.6.1. SUPAECAPolicyRuleComposite Attributes Currently, the SUPAECAPolicyRuleComposite class defines one attribute, as described in the following subsection. 6.6.1.1. The Attribute "supaECAEvalRuleStrategy" This is a mandatory, non-zero, integer attribute that enumerates a set of allowable alternatives that define how the set of SUPAPolicyAction object instances in a SUPAECAPolicyRuleComposite object are evaluated. It is assumed that the event and condition clauses of the SUPAECAPolicyRuleComposite have evaluated to TRUE (e.g., the event has occurred and the conditions were met). Values include: 0: error 1: init 2: execute the first SUPAPolicyAction in the SUPAECAPolicyRuleComposite object and then terminate 3: execute the last SUPAPolicyAction in the SUPAECAPolicyRuleComposite object and then terminate 4: execute only the highest priority SUPAPolicyAction(s) in the SUPAECAPolicyRuleComposite object and then terminate 5: execute all SUPAPolicyActions in prioritized order (if any) in that particular SUPAECAPolicyRuleComposite object, regardless of whether other SUPAPolicyActions succeed or fail 6: execute all SUPAPolicyActions in prioritized order (if any) in that particular SUPAECAPolicyRuleComposite object until at least one SUPAPolicyAction fails, and then terminate Note that 0 and 1 represent error and initialization states, respectively. Values 2 and 3 MUST execute a single SUPAPolicyAction, and then terminate execution of all SUPAPolicyActions in this SUPAECAPolicyRuleComposite object. Strassner, et al. Expires November 30, 2017 [Page 108]
Internet-Draft SUPA Generic Policy Model May 2017 If the value of the supaECAEvalStrategy attribute is 4, 5 or 6, then all SUPAPolicyActions that have a priority will be executed first, starting with the SUPAPolicyAction(s) that have the highest priority, and then descending in prioritized order. During this process, any SUPAPolicyActions that have the SAME priority MAY be executed in any order. After all SUPAPolicyActions that have an associated priority have executed, then all SUPAPolicyAction(s) that do not have a priority are then executed (in any order). Assume that a SUPAECAPolicyRuleComposite object contains three SUPAECAPolicyRuleAtomic objects as well as one SUPAECAPolicyRuleComposite object (that contains two SUPAECAPolicyRuleAtomic objects), as shown below. Z (SUPAECAPolicyRuleComposite) | +--A (SUPAECAPolicyRuleAtomic), priority 5 | +--B (SUPAECAPolicyRuleAtomic), priority 0 | +--C (SUPAECAPolicyRuleComposite), priority 10 | | | +--C1 (SUPAECAPolicyRuleAtomic), priority 2 | | | +--C2 (SUPAECAPolicyRuleAtomic), priority 1 | +--D (SUPAECAPolicyRuleAtomic), no priority Then, if the supaECAEvalStrategy attribute value of Z equals: 0: an error is issued 1: all SUPAPolicyActions MUST NOT be used (since their containing SUPAECAPolicyRuleComposite object is not properly initialized) 2: only SUPAPolicyAction A is executed 3: only SUPAPolicyAction D is executed 4: two SUPAPolicyActions are executed: C1, followed by C2 5: all SUPAPolicyActions are executed, regardless of any failures; the order of execution is C1, then C2, then A, then B, then D 6: all SUPAPolicyActions are executed until a failure is detected, and then execution for all SUPAPolicyActions terminate; the execution order (up to the occurrence of the failure) is C1, then C2, then A, then B, then D Note that the supaECAEvalRuleStrategy defines the same semantics as the supaECAPolActionEvalStrategy. The difference is that the former is applied to a SUPAECAPolicyRuleComposite object, and the latter is applied to a SUPAECAPolicyRuleAtomic object. Strassner, et al. Expires November 30, 2017 [Page 109]
Internet-Draft SUPA Generic Policy Model May 2017 6.6.2. SUPAECAPolicyRuleComposite Relationships Currently, the SUPAECAPolicyRuleComposite defines a single aggregation between it and SUPAECAPolicyRule, as described below. 6.6.2.1. The Aggregation "SUPAHasECAPolicyRule" This is an optional aggregation that implements the composite pattern. The multiplicity of this aggregation is 0..1 on the aggregate (SUPAECAPolicyRuleComposite) side and 1..n on the part (SUPAECAPolicyRule) side. This means that if this aggregation is defined, then at least one SUPAECAPolicyRule object (which may be either an instance of a SUPAECAPolicyRuleAtomic or a SUPAECAPolicyRuleComposite class) must also be instantiated and aggregated by this particular SUPAECAPolicyRuleComposite object. The semantics of this aggregation are defined by the SUPAHasECAPolicyRuleDetail association class. 6.6.2.2. The Association Class "SUPAHasECAPolicyRuleDetail" This is an optional concrete association class, and defines the semantics of the SUPHasECAPolicyRule aggregation. This enables the attributes and relationships of the SUPAHasECAPolicyRuleDetail class to be used to constrain which SUPAECAPolicyRule objects can be aggregated by this particular SUPAECAPolicyRuleComposite object instance. It contains a single attribute, defined below. 6.6.2.2.1. The Attribute "supaECAPolicyIsDefault" This is an optional Boolean attribute. If the value of this attribute is true, then this SUPAECAPolicyRule is a default policy, and will be executed if no other SUPAECAPolicyRule in the SUPAECAPolicyRuleComposite container has been executed. This is a convenient way for error handling, though care should be taken to ensure that only one default policy rule is defined per SUPAECAPolicyRuleComposite container. 6.7. The Abstract Class "SUPABooleanClause" A SUPABooleanClause specializes a SUPAPolicyClause, and defines a Boolean expression consisting of a standard structure in the form of a SUPAPolicyVariable, a SUPAPolicyOperator, and a SUPAPolicyValue. For example, this enables the following Boolean clause to be defined: Foo >= Baz where 'Foo' is a PolicyVariable, '>=' is a PolicyOperator, and 'Baz' is a PolicyValue. Strassner, et al. Expires November 30, 2017 [Page 109]
Internet-Draft SUPA Generic Policy Model May 2017 Note that in this approach, the SUPAPolicyVariable and SUPAPolicyValue terms are defined as an appropriate subclass of the SUPAPolicyComponentDecorator class; it is assumed that the SUPAPolicyOperator is an instance of the SUPAPolicyOperator class. This enables the EPRIM, in conjunction with the GPIM, to be used as a reusable class library. This encourages interoperability, since each element of the clause is itself an object defined by the SUPA object hierarchy. An entire SUPABooleanClause may be negated by setting the supaBoolClauseIsNegated class attribute of the SUPABooleanClause class to TRUE. Individual terms of a Boolean clause can be negated by using the supaTermIsNegated Boolean attribute in the SUPAPolicyTerm class (see section 5.10). A PolicyClause is in Conjunctive Normal Form (CNF) if it is a sequence of logically ANDed terms, where each term is a sequence of logically ORed terms. A PolicyClause is in Disjunctive Normal Form (DNF) if it is a sequence of logically ORed terms, where each term is a sequence of logically ANDed terms. The construction of more complex clauses, which consist of a set of simple clauses in CNF or DNF (as shown in the above example), is provided by using the composite pattern [3] to construct two concrete subclasses of the abstract SUPABooleanClause class. These are called SUPABooleanClauseAtomic and SUPABooleanClauseComposite, and are defined in sections 6.8 and 6.9, respectively. This enables instances of either a SUPABooleanClauseAtomic and/or a SUPABooleanClauseComposite to be aggregated into a SUPABooleanClauseComposite object. 6.7.1. SUPABooleanClause Attributes The SUPABooleanClause class currently defines three attributes, which are defined in the following subsections. 6.7.1.1. The Attribute "supaBoolClauseBindValue" This is a mandatory non-zero integer attribute, and defines the order in which terms bind to a clause. For example, the Boolean expression "((A AND B) OR (C AND NOT (D OR E)))" has the following binding order: terms A and B have a bind value of 1; term C has a binding value of 2, and terms D and E have a binding value of 3. 6.7.1.2. The Attribute "supaBoolClauseIsCNF" This is an optional Boolean attribute. If the value of this attribute is TRUE, then this SUPABooleanClauseComposite is in CNF form. Otherwise, it is in DNF form. Strassner, et al. Expires November 30, 2017 [Page 110]
Internet-Draft SUPA Generic Policy Model May 2017 6.7.1.3. The Attribute "supaBoolClauseIsNegated" This is a mandatory Boolean attribute. If the value of this attribute is TRUE, then this (entire) SUPABooleanClause is negated. Note that the supaPolTermIsNegated class attribute of the SUPAPolicyTerm class is used to negate a single term. 6.7.2. SUPABooleanClause Relationships Currently, no relationships are defined for this class. 6.8. The Concrete Class "SUPABooleanClauseAtomic" This is a mandatory concrete class that represents a SUPABooleanClause that can operate as a single, stand-alone, manageable object. A SUPABooleanClauseAtomic object can NOT be modeled as a set of hierarchical clauses; if this functionality is required, then a SUPABooleanClauseComposite object must be used. Examples of Boolean clauses that could be contained in a SUPABooleanClauseAtomic include P, NOT P, and (P OR Q), where P and Q are literals (e.g., a variable name that can be either true or false, or a formula that evaluates to a literal). Examples of Boolean clauses that are NOT in CNF are NOT(P AND Q), (P AND Q) OR R, and P AND (Q OR (R AND S)); their CNF equivalent forms are NOT P AND NOT Q, (P AND R) OR (Q AND R), and P AND (Q OR S) AND (Q OR S), respectively. 6.8.1. SUPABooleanClauseAtomic Attributes No attributes are currently defined for this class. 6.8.2. SUPABooleanClauseAtomic Relationships Currently, no relationships are defined for this class. 6.9. The Concrete Class "SUPABooleanClauseComposite" This is a mandatory concrete class that represents a SUPABooleanClause that can operate as a hierarchy of SUPAPolicyClause objects, where the hierarchy contains instances of SUPABooleanClauseAtomic and/or SUPABooleanClauseComposite objects. Each of the SUPABooleanClauseAtomic and SUPABooleanClauseComposite objects, including the outermost SUPABooleanClauseComposite object, are separately manageable. More importantly, each SUPABooleanClauseComposite object represents an aggregated object that is itself manageable. Strassner, et al. Expires November 30, 2017 [Page 111]
Internet-Draft SUPA Generic Policy Model May 2017 Examples of Boolean clauses that could be contained in a SUPABooleanClauseComposite object include ((P OR Q) AND R), and ((NOT P OR Q) AND (R OR NOT S) AND T), where P, Q, R, S, and T are literals. 6.9.1. SUPABooleanClauseComposite Attributes No attributes are currently defined for this class. 6.9.2. SUPABooleanClauseComposite Relationships Currently, the SUPABooleanClauseComposite class defines a single aggregation, which is described in the following subsection. 6.9.2.1. The Aggregation "SUPAHasBooleanClause" This is a mandatory aggregation that defines the set of SUPABooleanClause objects that are aggregated by this SUPABooleanClauseComposite object. The multiplicity of this relationship is 0..1 on the aggregate (SUPABooleanClauseComposite) side, and 1..n on the part (SUPABooleanClause) side. This means that one or more SUPABooleanClauses are aggregated and used to define this SUPABooleanClauseComposite object. The 0..1 cardinality on the SUPABooleanClauseComposite side is necessary to enable SUPABooleanClauses to exist (e.g., in a PolicyRepository) before they are used by a SUPABooleanClauseComposite. The semantics of this aggregation is defined by the SUPAHasBooleanClauseDetail association class. 6.9.2.2. The Association Class "SUPAHasBooleanClauseDetail" This is a mandatory concrete association class that defines the semantics of the SUPAHasBooleanClause aggregation. This enables the attributes and relationships of the SUPAHasBooleanClauseDetail class to be used to constrain which SUPABooleanClause objects can be aggregated by this particular SUPABooleanClauseComposite object instance. 6.9.2.2.1. The Attribute "supaIsHornClause" This is an optional attribute of type Boolean. If the value of this attribute is TRUE, then this SUPABooleanClause is a Horn clause. This has important properties for logic programming and model theory. For example, a Horn clause is able to express implication of one variable from a set of other variables. Strassner, et al. Expires November 30, 2017 [Page 112]
Internet-Draft SUPA Generic Policy Model May 2017 6.10. The Abstract Class "SUPAECAComponent" This is a mandatory abstract class that defines three concrete subclasses, one each to represent the concepts of reusable events, conditions, and actions. They are called SUPAPolicyEvent, SUPAPolicyCondition, and SUPAPolicyAction, respectively. SUPAECAComponents provide two different ways to construct SUPAPolicyClauses. The first is for the SUPAECAComponent to be used as either a SUPAPolicyVariable or a SUPAPolicyValue, and the second is for the SUPAECAComponent to contain the entire clause text. For example, suppose it is desired to define a policy condition clause with the text 'queueDepth > 10'. Two approaches could satisfy this as follows: Approach #1 (canonical form): SUPAPolicyCondition.supaPolicyConditionData contains the text 'queueDepth' SUPAPolicyOperator.supaPolOpType is set to '1' (greater than) SUPAPolicyValue.supaPolValContent is set to '10' Approach #2 (SUPAECAComponent represents the entire clause): SUPAPolicyCondition.supaPolicyConditionData contains the text 'queueDepth > 10' The class attribute supaECACompIsTerm, defined in subsection 6.10.1.1, is used to identify which of these two approaches is used by an object instance of this class. 6.10.1. SUPAECAComponent Attributes A single attribute is currently defined for this class, and is described in the following subsection. 6.10.1.1. The Attribute "supaECACompIsTerm" This is an optional Boolean attribute. If the value of this attribute is TRUE, then this SUPAECAComponent is used as the value of a SUPAPolicyTerm to construct a SUPAPolicyClause (this is approach #1 in section 6.10 above). If the value of this attribute is FALSE, then this SUPAECAComponent contains the text of the entire corresponding SUPAPolicyClause (this is approach #2 in section 6.10 above). 6.10.2. SUPAECAComponent Relationships No relationships are currently defined for this class. Strassner, et al. Expires November 30, 2017 [Page 113]
Internet-Draft SUPA Generic Policy Model May 2017 6.11. The Concrete Class "SUPAPolicyEvent" This is a mandatory concrete class that represents the concept of an Event that is applicable to a policy management system. Such an Event is defined as anything of importance to the management system (e.g., a change in the system being managed and/or its environment) occuring on a time-axis (as defined in [19]). It should be noted that instances of this class are not themselves events. Rather, instances of this class appear in SUPAPolicyClauses to describe what types of events the SUPAPolicy is triggered by and/or uses. SUPAPolicyEvents can be used as part of a SUPAPolicyClause; this is done by specifying the attribute name and value of an Event in the supaPolicyEventData attribute of the SUPAPolicyEvent. This enables event attributes to be used as part of a SUPAPolicyClause. Information from events that trigger SUPAPolicies need to be made available for use in condition and action clauses, as well as inappropriate decorator objects. Subclasses (such as one for using YANG notifications as policy events) need to define how the iformation from the environment or event is used to populate variables that can be used by decorator, condition, or action objects. 6.11.1. SUPAPolicyEvent Attributes Currently, five attributes are defined for the SUPAPolicyEvent class, which are described in the following subsections. 6.11.1.1. The Attribute "supaPolicyEventData[1..n]" This is a mandatory attribute that defines an array of strings. Each string in the array represents an attribute name and value of an Event object. The format of each string is defined as name:value. The 'name' part is the name of the SUPAPolicyEvent attribute, and the 'value' part is the value of that attribute. Note: [1..n] means that this is a multi-valued property that has at least one (and possibly more) attributes. For example, if this value of this attribute is: {(startTime:0800), (endTime:1700), (date:2016-05-11), (timeZone:-08:00)} then this attribute contains four properties, called startTime, endTime, date, and timeZone, whose values are 0800, 1700, May 11 2016, and Pacific Standard Time, respectively. Strassner, et al. Expires November 30, 2017 [Page 114]
Internet-Draft SUPA Generic Policy Model May 2017 This attribute works with another class attribute, called supaPolicyEventEncoding, which defines how to interpret this attribute. These two attributes form a tuple, and together enable a machine to understand the syntax and value of the data carried by the object instance of this class. 6.11.1.2. The Attribute "supaPolicyEventEncoding" This is a mandatory non-zero enumerated integer attribute, and defines how to interpret the supaPolicyEventData class attribute. These two attributes form a tuple, and together enable a machine to understand the syntax and value of the data carried by the object instance of this class. Values include: 0: error 1: init 2: String 3: Integer 4: Boolean 5: Floating Point 6: DateTime 7: Object referenced by GUID 8: Object referenced by URI 9: Object referenced by FQDN 10: Object referenced by FQPN 11: Object referenced by string_instance_id Enumerations 0 and 1 signify an error state and an initialization state, respectively. Enumerations 2-6 define fundamental data types; for example, the event payload could carry such a value. The final five enumerations define an object reference. The value 11 defines the canonical representation, in ASCII, of an instance ID of this object. 6.11.1.3. The Attribute "supaPolicyEventIsPreProcessed" This is an optional Boolean attribute. If the value of this attribute is TRUE, then this SUPAPolicyEvent has been pre- processed by an external entity, such as an Event Service Bus, before it was received by the Policy Management System. 6.11.1.4. The Attribute "supaPolicyEventIsSynthetic" This is an optional Boolean attribute. If the value of this attribute is TRUE, then this SUPAPolicyEvent has been produced by the Policy Management System. If the value of this attribute is FALSE, then this SUPAPolicyEvent has been produced by an entity in the system being managed. Strassner, et al. Expires November 30, 2017 [Page 115]
Internet-Draft SUPA Generic Policy Model May 2017 6.11.1.5. The Attribute "supaPolicyEventTopic[0..n]" This is a mandatory array of string attributes, and contains the subject that this PolicyEvent describes. Note: [0..n] means that this is a multi-valued property that has zero or more attributes. 6.11.2. SUPAPolicyEvent Relationships No relationships are currently defined for this class. 6.12. The Concrete Class "SUPAPolicyCondition" This is a mandatory concrete class that represents the concept of an Condition that will determine whether or not the set of Actions in the SUPAECAPolicyRule to which it belongs are executed or not. Condition clauses needs to be able to access information fromhe the policy environment (e.g., the network element or policy engine applying the policy) or the triggering event. This may be done using SUPAPolicyVariable objects as decorators. If the subclass of a SUPAPolicyCondition uses some other encoding, the definition of that class needs to indicate how information from the environment or event will be used. SUPAPolicyConditions can be used as part of a SUPAPolicyClause (e.g., var = SUPAPolicyCondition.supaPolicyConditionData) or as a standalone SUPAPolicyClause (e.g., the supaPolicyConditionData attribute contains text that defines the entire condition clause). This is defined in the supaECACompIsTerm attribute of the SUPAECAComponent class (see section 6.10). 6.12.1. SUPAPolicyCondition Attributes Currently, two attributes are defined for the SUPAPolicyCondition class, which are described in the following subsections. 6.12.1.1. The Attribute "supaPolicyConditionData[1..n]" This is a mandatory array of string attributes that contains the content of this SUPAPolicyCondition object. Note: [1..n] means that this is a multi-valued property that has at least one (and possibly more) attributes. If this class is instantiated, then this attribute SHOULD also be instantiated, and SHOULD be part of a conformant implementation. Strassner, et al. Expires November 30, 2017 [Page 116]
Internet-Draft SUPA Generic Policy Model May 2017 6.12.1.2. The Attribute "supaPolicyConditionEncoding" This is a mandatory non-zero enumerated integer attribute, and defines the data type of the supaPolicyConditionData attribute. These two attributes form a tuple, and together enable a machine to understand the syntax and value of the content of this SUPAPolicyCondition object. Values include: 0: error 1: init 2: OCL 2.4 3: OCL 2.x 4: OCL 1.x 5: QVT 1.2 - Relations Language 6: QVT 1.2 - Operational language 7: Alloy 8: ASCII Text Enumerations 0 and 1 signify an error state and an initialization state, respectively. Enumerations 2-4 are dedicated to OCL (with OCL 2.4 being the latest version as of this writing). QVT defines a set of languages [20] (the two most powerful and useful are defined by enumerations 5 and 6). Alloy is a language for describing constraints, and uses a SAT solver to guarantee correctness [21]. Enumeration 8 (ASCII Text) is not recommended (since it is informal, and hence, not verifiable), but is included for completeness. If this class is instantiated, then this attribute SHOULD also be instantiated, and SHOULD be part of a conformant implementation. 6.12.2. SUPAPolicyCondition Relationships No relationships are currently defined for this class. 6.13. The Concrete Class "SUPAPolicyAction" This is a mandatory concrete class that represents the concept of an Action, which is a part of a SUPAECAPolicyRule. The Action MAY be executed when both the event and the condition clauses of its owning SUPAECAPolicyRule evaluate to true. Action clauses needs to be able to access information fromhe the policy environment (e.g., the network element or policy engine applying the policy) or the triggering event. This may be done using SUPAPolicyVariable objects as decorators. If the subclass of a SUPAPolicyAction uses some other encoding, the definition of that class needs to indicate how information from the environment or event will be used. Strassner, et al. Expires November 30, 2017 [Page 117]
Internet-Draft SUPA Generic Policy Model May 2017 The execution of this action is determined by its SUPAPolicy container, and any applicable SUPAPolicyMetadata objects. SUPAPolicyActions can be used in three different ways: o as part of a SUPAPolicyClause (e.g., var = SUPAPolicyAction.supaPolicyActionData) o as a standalone SUPAPolicyClause (e.g., the supaPolicyActionData attribute contains text that defines the entire action clause) o to invoke one or more SUPAPolicyActions in a different SUPAECAPolicyRule In the third case, the execution semantics should not be affected, since all SUPAPolicyActions are reusable objects. Note that this is NOT invoking a different SUPAECAPolicyRule, but rather, invoking a SUPAPolicyAction that is contained in a different SUPAECAPolicyRule. 6.13.1. Restrictions about SUPAPolicyActions Calling SUPAPolicies There was confusion as to whether a SUPAPolicyAction could call a SUPAPolicy or not. While this appears attractive, it presents several difficult conceptual problems concerning what element has the scope of control. These problems are not solved in [RFC3460]. Consider the following scenario: o Policy A is currently executing o Action A1 executes successfully o Action A2 calls Policy B o Action A3 is either waiting to execute, or is executing When Policy B is called, it presumably should execute under the scope of control of Policy A (since Policy A has not finished executing). However, calling another **ECAPolicyRule** means that now, the event clause of Policy B should be activated. It is very difficult to ensure that the next thing the Policy Engine does is determine if the event clause of B is satisfied or not. Furthermore, what happens to Action A3? Is Policy B supposed to finish execution before Action A3? This requires additional logic (priorities do not work here!), which requires communication between the policy engine and both Policies A and B. Even if these problems are solved, what happens if Action A3 fails, and the supaPolExecFailStrategy has a value of 2 (i.e., if an action fails, then a rollback must be performed)? Does Policy BCP also get rolled back? Therefore, for this version of SUPA, a SUPAPolicyAction can only call another SUPAPolicyAction. Strassner, et al. Expires November 30, 2017 [Page 118]
Internet-Draft SUPA Generic Policy Model May 2017 6.13.2. SUPAPolicyAction Attributes Currently, two attributes are defined for the SUPAPolicyCondition class, which are described in the following subsections. 6.13.2.1. The Attribute "supaPolicyActionData[1..n]" This is a mandatory array of string attributes that contains the content of this SUPAPolicyAction object. This attribute works with another class attribute, called supaPolicyActionEncoding, which defines how to interpret this attribute. These two attributes form a tuple, and together enable a machine to understand the syntax and value of the data carried by the object instance of this class. Note: [1..n] means that this is a multi-valued property that has at least one (and possibly more) attributes. Since this attribute could represent a term in a SUPAPolicyClause (e.g., var = SUPAPolicyAction.supaPolicyActionData), a complete SUPAPolicyClause (e.g., the supaPolicyActionData attribute contains text that defines the entire action clause), or the name of a SUPAPolicyAction to invoke, each element in the string array is prepended with one of the following strings: o 't:' (or 'term:'), to denote a term in a SUPAPolicyClause o 'c:' (or 'clause:'), to denote an entire SUPAPolicyClause o 'a:' (or 'action:'), to invoke a SUPAPolicyAction in a a different SUPAECAPolicyRule Note that in the third case, the text must identify a unique SUPAPolicyAction (e.g., the location of the SUPAPolicyAction, including its containing SUPAPolicy if applicable, MUST be specified). 6.13.2.2. The Attribute "supaPolicyActionEncoding" This is a mandatory non-zero enumerated integer attribute, and defines the data type of the supaPolicyActionData attribute. This attribute works with another class attribute, called supaPolicyActionData, which contains the content of the action. These two attributes form a tuple, and together enable a machine to understand the syntax and value of the content of this SUPAPolicyAction object. Values include: 0: error 1: init 2: OCL 2.4 3: OCL 2.x 4: OCL 1.x Strassner, et al. Expires November 30, 2017 [Page 119]
Internet-Draft SUPA Generic Policy Model May 2017 5: QVT 1.2 - Relations Language 6: QVT 1.2 - Operational language 7: Alloy 8: ASCII Text 9: GUID 10: UUID 11: URI 12: FQDN 13: FQPN update me Enumerations 0 and 1 signify an error state and an initialization state, respectively. Enumerations 2-4 are dedicated to OCL (with OCL 2.4 being the latest version as of this writing). QVT defines a set of languages [20] (the two most powerful and useful are defined by enumerations 5 and 6). Alloy is a language for describing constraints, and uses a SAT solver to guarantee correctness [21]. Enumeration 8 (ASCII Text) is not recommended (since it is informal, and hence, not verifiable), but is included for completeness. Enumerations 9-12 define a reference to the SUPAPolicyAction. If this class is instantiated, then this attribute SHOULD also be instantiated, and SHOULD be part of a conformant implementation. 6.13.3. SUPAPolicyAction Relationships No relationships are currently defined for this class. It inherits the relationships defined by the SUPAPolicyComponentDecorator (see section 5.7.3.). Enumerations 1-4 are used to provide a reference to an action object. Enumerations 5-10 are used to express the action to perform as a string. Strassner, et al. Expires November 30, 2017 [Page 120]
Internet-Draft SUPA Generic Policy Model May 2017 7. Examples This section contains some examples that show how to use various objects in this draft to build policy rules. 7.1. Example 1: Blocking SNMP Traffic This example will illustrate how to use the SUPA information model to block inbound and outbound SNMP traffic. 7.1.1. Introduction The following exemplar policy was posted to the SUPA list: ensure that SNMP is blocked on ports at the edgeInterface of the administrative domain to prevent SNMP going out or coming in from outside the enterprise. (1) While this is simple for a human to understand, it is actually quite difficult for a machine to understand in its original form. This is because: 1) the text must be translated to a form that the device can understand 2) the nature of the policy is not clear (due to the inherent ambiguity of English) 7.1.2. Solution Approach First, let's assume the following context: +-----------------------------+ +--------------+ | Enterprise Domain | | Other Domain | | | | | | +-----+ +-----+ +-----+ |/ \| | | | NE1 | | NE2 | | NE3 +--+-------+ | | +-----+ +-----+ +-----+ |\ /| | +-----------------------------+ +--------------+ In the above example, the only "edge" interface is that of NE3. This enables us to simplify (1) to: block SNMP on NE3 (2) This assumes that NE3 exists and is operational. This is a **big** assumption. This leads to the observation that in both (1) and (2), there are at least two different interpretations for each: 1) apply a set of actions directly to a SUPAPolicyTarget, assuming that the SUPAPolicyTarget understands SUPAPolicies, or 2) apply a set of desired actions that are already translated to a form that a SUPAPolicyTarget can understand Strassner, et al. Expires November 30, 2017 [Page 121]
Internet-Draft SUPA Generic Policy Model May 2017 Note that a SUPAPolicyTarget could be the network device or a proxy for the network device. The difference between these interpretations is whether a SUPAPolicy applies one or more SUPAPolicyActions **directly** to a SUPAPolicyTarget (that is without translation to, for example, CLI or YANG) versus whether a SUPAPolicy, as part of its action(s), produces something that the device (or its proxy) can understand. Put another way, the first alternative shows how SUPAPolicies can directly control behavior, while the second alternative shows how a SUPAPolicy can invoke a set of actions that the device (or its proxy) can understand. Thus, policy (1) can be formulated as either: - IF any network element has a port that meets the criterion of the role "edge interface", AND it is inside the EnterpriseDomain, then block SNMP traffic (3) - IF a network element is added within the EnterpriseDomain IF any of its ports take on the role "edge interface" Add a filter to block SNMP traffic for that port (4) The first case is the simplest, and likely what most people thought. Conceptually, it could look as follows: Event: SNMP traffic is sent or received Condition: IF this port implements the "edgeInterface" role AND IF this port is IN the EnterpriseDomain Action: Block SNMP traffic (5) (We will define "edgeInterface" role and "EnterpriseDomain" later in this note.) A possible drawback of (5) is that it is activated by the arrival of a packet event. Such events will be VERY common, meaning that the Policy Engine will be doing a lot of work when most of the time, no policy action is needed. The second case could be addressed as follows: Event: A new port is going to be enabled Condition: IF this interface implements the "edgeInterface" role AND IF this port is IN the EnterpriseDomain Action: InstallFilter("SNMP traffic filter", "block") (6) 7.1.3. Solution for Case 1 (SUPAPolicies Control Behavior) This section describes the strategy for, and outlines the steps taken, to build one exemplar implementation of (5). Strassner, et al. Expires November 30, 2017 [Page 122]
Internet-Draft SUPA Generic Policy Model May 2017 7.1.3.1. Strategy The strategy is to build three clauses, one each to represent the event, condition, and action clauses of our SUPAECAPolicyRule. These are realized by three different **objects**, and aggregated by the SUPAECAPolicyRule (a 4th object) using three different aggregations. Each aggregation is an instance of SUPAHasPolicyClause. This yields a structure similar to that in Figure 7 of the SUPA information model, and is shown below: C C +-------------------------+ +----------------------------+/ | SUPABooleanClauseAtomic | | SUPABooleanClauseComposite +----+ +-------------+-----------+ +----------+-----------------+\ | I I | I I SUPAHasBooleanClause | +---------------------------+ | I | C I | +-------------------------+ A \ / | | SUPAECAPolicyRuleAtomic | +------+------------+/ \ | +-------------+-----------+ | SUPABooleanClause + A ------+ I +--------+----------+\ / I I I I A \ / A \ / +--------+----------+ +--------+-----------+ | SUPAECAPolicyRule | | SUPAPolicyClause | +--+----+----+------+ +-------+----+----+--+ / \ / \ / \ 1..n 0..n / \ / \ / \ A A A | | | \ / \ / \ / | | | | | | | | | | | | SUPAHasPolicyClause #1 | | | | | +--------------------------+ | | | | | | | | SUPAHasPolicyClause #2 | | | +------------------------------------+ | | | | SUPAHasPolicyClause #3 | +----------------------------------------------+ Note: all 3 aggregations have a multiplicity of 1..n - 0..n Figure 29. Creating a SUPAECAPolicyRule Strassner, et al. Expires November 30, 2017 [Page 123]
Internet-Draft SUPA Generic Policy Model May 2017 In Figure 29, the event, condition, and action clauses are represented by the SUPAHasPolicyClause aggregations (#1 - #3). The association classes for these three aggregations are not shown; this is because there are no additional semantics required to define the meaning of each aggregation. This also applies to the SUPAHasBooleanClause in the top right of the above figure. Finally, recall that the "I" arrows stand for inheritance. Hence, both the SUPABooleanClauseAtomic and SUPABooleanClauseComposite classes inherit from SUPABooleanClause, which inherits from SUPAPolicyClause. Another important point to remember in Figure 29 is that classes inherit both attributes and relationships from their superclasses. For example, the SUPAECAPolicyRuleAtomic, as well as both the SUPABooleanClauseAtomic and the SUPABooleanClauseComposite, all inherit the SUPAHasPolicyClause aggregation. More specifically, the SUPAECAPolicyRuleAtomic can aggregate SUPAPolicyClauses, and any type of SUPAPolicyClause can be aggregated by any type of SUPAPolicyStructure (not shown in the Figures; recall that this is the superclass of SUPAECAPolicyRule). The decorator pattern (see Section 4.2.1.2) enables the SUPAPolicyClause (or any of its concrete subclasses) to be optionally wrapped by one or more SUPAPolicyComponentDecorator objects. We will use this feature to adorn the SUPABooleanPolicyClauseAtomic object with one or more SUPAPolicyEvent, SUPAPolicyCondition, and SUPAPolicyAction objects. 7.1.3.2. Implementation Let's build up the representation of (5) using SUPA objects. The SUPAECAPolicyRule is simple - it is just a SUPAECAPolicyRuleAtomic object (see Section 6.5). The SUPAECAPolicyRuleAtomic, as opposed to the SUPAECAPolicyRuleComposite, subclass of SUPAECAPolicyRule is used because there is no need to create a hierarchy of rules. This means that there is no need to instantiate the SUPAECAPolicyRuleComposite class or its SUPAHasECAPolicyRule aggregation for this example. There are several ways to build SUPAPolicyClauses. The following will show two different ways to build individual clauses. Our approach will be to model the event and action clauses as single SUPABooleanClauseAtomic objects, and then model the condition clause as a SUPABooleanClauseComposite object. This is just to show how different parts of the model can be used. The event clause is a Boolean AND of two values; we choose to represent it as a textual string (see Section 6.10). => this means that SUPAECAComponent.supaECACompIsTerm is FALSE Strassner, et al. Expires November 30, 2017 [Page 124]
Internet-Draft SUPA Generic Policy Model May 2017 Both events (SNMP inbound and outbound traffic) can be represented by SUPAPolicyEvents (see Section 6.11) as follows (we are just showing the inbound event; the outbound event is identical except that the value of supaPolicyEventData is '{"SNMP outbound"}'): => supaPolicyEventData is {"SNMP inbound"} => supaPolicyEventEncoding is 2 // string => supaPolicyEventIsPreProcessed is FALSE => supaPolicyEventIsSynthetic is FALSE => supaPolicyEventTopic is {"SNMP traffic"} Here, we chose to instantiate all attributes (mandatory and optional) for the sake of completeness (the first, second, and fifth attributes are all mandatory). The condition clause is also a Boolean AND of two values. The first part of the Boolean clause will test that a device's (sub)-interface belongs to a Role called edgeInterfaceRole, logically ANDed with it sending or receiving SNMP traffic. The following two definitions help clarify the first concept: - a Role is an abstraction that defines a set of functionality, behavior, and responsibilities that an object can take on at any time during its lifecycle. Roles enable the developer to adapt an object to different client's needs through transparently attached Role objects, each one representing a Role the object has to play in that client's context. This decouples the needs of different applications from each other. - an "edge interface" is a Role that represents a set of device (sub)-interfaces that connect two different domains to each other (e.g., router interfaces that connect the Enterprise to the Internet). In this example, the Role is populated by information that is provided from the received event and/or from the current environment (e.g., a topology model). Hence, the first condition clause can be written as: (((port == 161) OR (port == 162)) AND (interfaceRole == "edge")) This can be modeled in a variety of ways in SUPA; the simplest is as a SUPAPolicyCondition (see Section 6.12), as follows: => SUPAECAComponent.supaECAIsTerm is FALSE => supaPolicyConditionData is {"(((port == 161) OR (port == 162)) AND (interfaceRole == "edge"))"} => supaPolicyConditionEncoding is 8 // ASCII text Strassner, et al. Expires November 30, 2017 [Page 125]
Internet-Draft SUPA Generic Policy Model May 2017 For the second condition clause, we choose to again dramatically simplify it by mapping "EnterpriseDomain" to a particular IP subnet. This can also be modeled as a single string in a SUPAPolicyCondition, as follows: => SUPAECAComponent.supaECAIsTerm is FALSE => supaPolicyConditionData is {"IPAddress IN 204.17.5.0/27"} => supaPolicyConditionEncoding is 8 // ASCII text Each of the SUPAPolicyCondition objects decorates a separate instance of a SUPABooleanClauseAtomic object. The three SUPABooleanClauseAtomic objects are then aggregated by a single SUPABooleanClauseComposite object (see Section 6.9). This works because both are concrete subclasses of SUPAPolicyClause, and thus, both inherit the ability to have objects decorate it. This is shown in Figure 30: A +------------------------------+ 1..n | SUPAPolicyComponentStructure +----------------------+ +----------------+-------------+ | / \ | I SUPAHasDecoratedPolicyComponent | I | +--------------+-----------+ | I I | A I A I | +---------+--------+ +--------------+---------------+ 0..1 | | | | |/ \ | | SUPAPolicyClause | | SUPAPolicyComponentDecorator + A -----+ | | | |\ / +---------+--------+ +--------------+---------------+ / \ / \ I I A I A I \+----------+--------+ +---------+--------+ +----+ SUPABooleanClause | | SUPAECAComponent | | /+----------+--------+ +---------+--------+ | / \ / \ | I I | I I | +---+-------+ +----+------+------------+ | I I I I I | C I C I C I C I C I | +---+-----+ +---+----+ +----+---+ +-----+-----+ +----+---+ | / \| SUPA | | SUPA | | SUPA | | SUPA | | SUPA | +---- A + Boolean | | Boolean| | Policy | | Policy | | Policy | \ /| Clause | | Clause | | Event | | Condition | | Action | |Composite| | Atomic | +--------+ +-----------+ +--------+ +---------+ +--------+ Figure 30. Pertinent Classes for Decoration Strassner, et al. Expires November 30, 2017 [Page 126]
Internet-Draft SUPA Generic Policy Model May 2017 The three SUPABooleanClauseAtomic objects each have their supaBoolClauseIsCNF attributes set to TRUE, and their supaBoolClauseIsNegated attributes set to FALSE. The supaBoolClauseBindValue attributes of each are: => 1 for "((port == 161) OR (port == 162))" => 2 for "(interfaceRole == "edge")" => 3 for "("IPAddress IN 204.17.5.0/27")" The first term is shown in Figure X3 below: C +--------------------------------------+ | SUPABooleanClauseAtomic | | C | | +----------------------------------+ | | | SUPAPolicyCondition | | | | | | | | ((port == 161) OR (port == 162)) | | | +----------------------------------+ | +--------------------------------------+ Figure 31. Construction of a Condition Clause Figure 31 represents the SUPAPolicyCondition object wrapping the SUPABooleanClauseAtomic object (see Section 4.3.5). The combination of all three SUPABooleanClauseAtomic objects are then aggregated by a single SUPABooleanClauseComposite object, as shown in Figure 32. The action clause uses a SUPAPolicyAction (see Section 6.13) as follows: => supaPolicyActionData = {"clause: deny"} => supaPolicyActionEncoding is 8 // ASCII text 7.1.4. Solution for Case 2 (SUPAPolicies Do Not Control Behavior) This use case is different, in that its objective is to define a SUPAPolicyAction that is directly readable by a SUPAPolicyTarget. In this example, our SUPAPolicy will invoke a NetConf operation to install a new feature (e.g., an ACL for blocking SNMP traffic) for **any** device whose (sub-)interface takes on the edgeInterface role and that is transmitting or receiving SNMP traffic. 7.1.4.1. Approach Once again, we can use a SUPAECAPolicyRuleAtomic object to represent the SUPAPolicy. This time, we create a new subclass of SUPAPolicyAction, called SUPAPolicyActionNetConf, which is capable of executing NetConf operations. Strassner, et al. Expires November 30, 2017 [Page 127]
Internet-Draft SUPA Generic Policy Model May 2017 C +--------------------------------+ | SUPABooleanClauseComposite | +----+----------+----------+-----+ / \ / \ / \ A A A \ / \ / \ / | | | | | | | | +------------------+ C \ / +---------+ | +--------+----------------+ | | | SUPABooleanClauseAtomic | | | | ( port condition ) | | | +-------------------------+ | | | | C \ / | +------------+------------+ | | SUPABooleanClauseAtomic | | | ( interface role ) | | +-------------------------+ | | C \ / +------------+------------+ | SUPABooleanClauseAtomic | | ( IP address ) | +-------------------------+ Figure 32. Construction of the Condition Clause 7.1.4.2. Implementation The SUPAPolicy is again made up of three clauses, one each to represent the event, condition, and action parts of our SUPAECAPolicyRule. The event clause is a simple Boolean clause; the easiest way to implement it is as a SUPAPolicyEvent (see Section 6.11) as follows: => supaPolicyEventData is {"enable port"} => supaPolicyEventEncoding is 2 // string => supaPolicyEventIsPreProcessed is FALSE => supaPolicyEventIsSynthetic is FALSE => supaPolicyEventTopic is {"new port event"} The condition clause is the same as in section 7.1.3.2. The action clause is more involved. We want to enable SUPA to use NetConf operations, so the easiest thing to do is to create a new subclass of SUPAPolicyAction, called SUPAPolicyActionNetConf. Strassner, et al. Expires November 30, 2017 [Page 128]
Internet-Draft SUPA Generic Policy Model May 2017 This is a concrete class, and has the following attributes (more could be added, of course): => supaPolNetConfContent => supaPolNetConfOperation => supaPolNetConfURL The supaPolNetConfContent attribute contains an XML document that will insert (for example) an ACL into the network device (or tell the proxy for the device to do so). The supaPolNetConfOperation attribute defines the RPC operation that will be performed. The supaPolNetConfURL attribute is an XPath expression that defines what is being manipulated (in this case, the desired device interface). In this example, the SUPAPolicyNetConfOperation will have an XPath expression that selects the new edge interface. The RPC operation is responsible for writing the ACL, and the content is the ACL, which drops traffic on the SNMP UDP ports. Strassner, et al. Expires November 30, 2017 [Page 129]
Internet-Draft SUPA Generic Policy Model May 2017 8. Security Considerations This document defines an object-oriented information model for describing policy information that is independent of any specific repository, language, or protocol. This document does not define any particular system implementation, including a protocol. Hence, it does not have any specific security requirements. 9. IANA Considerations This document has no actions for IANA. 10. Contributors The following people contributed to creating this document, and are listed in alphabetical order: Jason Coleman 11. Acknowledgments This document has benefited from reviews, suggestions, comments and proposed text provided by the following members, listed in alphabetical order: Andy Bierman, Bert Wijnen, Bob Natale, Dave Hood, Fred Feisullin, Georgios Karagiannis, Liu (Will) Shucheng, Marie-Jose Montpetit. 12. References This section defines normative and informative references for this document. 12.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. Strassner, et al. Expires November 30, 2017 [Page 130]
Internet-Draft SUPA Generic Policy Model May 2017 12.2. Informative References [RFC3060] Moore, B., Ellesson, E., Strassner, J., Westerinen, A., "Policy Core Information Model -- Version 1 Specification", RFC 3060, February 2001 [RFC3198] Westerinen, A., Schnizlein, J., Strassner, J., Scherling, M., Quinn, B., Herzog, S., Huynh, A., Carlson, M., Perry, J., Waldbusser, S., "Terminology for Policy-Based Management", RFC 3198, November, 2001 [RFC3460] Moore, B., ed., "Policy Core Information Model (PCIM) Extensions, RFC 3460, January 2003 [1] Strassner, J., "Policy-Based Network Management", Morgan Kaufman, ISBN 978-1558608597, Sep 2003 [2] Strassner, J., ed., "The DEN-ng Information Model", add stable URI [3] Riehle, D., "Composite Design Patterns", Proceedings of the 1997 Conference on Object-Oriented Programming Systems, Languages and Applications (OOPSLA '97). ACM Press, 1997, Page 218-228 [4] DMTF, CIM Schema, v2.44, http://dmtf.org/standards/cim/cim_schema_v2440 [5] Strassner, J., ed., "ZOOM Policy Architecture and Information Model Snapshot", TR235, part of the TM Forum ZOOM project, October 26, 2014 [6] TM Forum, "Information Framework (SID), GB922 and associated Addenda, v14.5, https://www.tmforum.org/information-framework-sid/ [7] Liskov, B.H., Wing, J.M., "A Behavioral Notion of subtyping", ACM Transactions on Programming languages and Systems 16 (6): 1811 - 1841, 1994 [8] Klyus, M., Strassner, J., Liu, W., Karagiannis, G., Bi, J., "SUPA Value Proposition", draft-klyus-supa-value-proposition-00, March 21, 2016 [9] ISO/IEC 10746-3 (also ITU-T Rec X.903), "Reference Model Open Distributed Processing Architecture", April 20, 2010 Strassner, et al. Expires November 30, 2017 [Page 131]
Internet-Draft SUPA Generic Policy Model May 2017 [10] Davy, S., Jennings, B., Strassner, J., "The Policy Continuum - A Formal Model", Proc. of the 2nd Intl. IEEE Workshop on Modeling Autonomic Communication Environments (MACE), Multicon Lecture Notes, No. 6, Multicon, Berlin, 2007, pages 65-78 [11] Gamma, E., Helm, R., Johnson, R., Vlissides, J., "Design Patterns - Elements of Reusable Object-Oriented Software", Addison-Wesley, 1994, ISBN 0-201-63361-2 [12] Strassner, J., de Souza, J.N., Raymer, D., Samudrala, S., Davy, S., Barrett, K., "The Design of a Novel Context-Aware Policy Model to Support Machine-Based Learning and Reasoning", Journal of Cluster Computing, Vol 12, Issue 1, pages 17-43, March, 2009 [13] http://csrc.nist.gov/projects/iden_ac.html [14] Martin, R.C., "Agile Software Development, Principles, Patterns, and Practices", Prentice-Hall, 2002, ISBN: 0-13-597444-5 [15] Halpern, J., Strassner, J., "Generic Policy Data Model for Simplified Use of Policy Abstractions (SUPA)" draft-ietf-supa-generic-policy-data-model-03, April 15, 2017 [16] Wang, Y., Esposito, F., Matta, I., Day, J., "RINA: An Architecture for Policy-based Dynamic Service Management", Tech Report BUCS-TR-2013-014, 2013 [17] Meyer, B., "Object-Oriented Software Construction", Prentice Hall, second edition, 1997 ISBN 0-13-629155-4 [18] http://semver.org/ [19] ISO/IEC:2004(E), "Data elements and interchange formats -- Information interchange -- Representation of dates and times", 2004 [20] http://www.omg.org/spec/QVT/ [21] http://alloy.mit.edu/alloy/ [22] Basile, C., and Lioy, A., "Analysis of Application- Layer Filtering Policies with Application to HTTP", IEEE/ACM Transactions on Networking, Vol 23, Issue 1, February 2015 Strassner, et al. Expires November 30, 2017 [Page 132]
Internet-Draft SUPA Generic Policy Model May 2017 [23] van Lunteren, J., and Engbersen, T., "Fast and Scalable Packet Classification", IEEE Journal on Selected Areas in Communication, vol 21, Issue 4, September 2003 [24] perldoc.perl.org [25] ISO/IEC/IEEE 9945, "Information technology - Portable Operating System Interface (POSIX) Base Specifications, Issue 7", September, 2009 Authors' Addresses John Strassner Huawei Technologies 2330 Central Expressway Santa Clara, CA 95138 USA Email: john.sc.strassner@huawei.com Joel Halpern Ericsson P. O. Box 6049 Leesburg, VA 20178 Email: joel.halpern@ericsson.com Sven van der Meer LM Ericsson Ltd. Ericsson Software Campus Garrycastle Athlone N37 PV44 Ireland Email: sven.van.der.meer@ericsson.com Strassner, et al. Expires November 30, 2017 [Page 133]
Internet-Draft SUPA Generic Policy Model May 2017 Appendix A. Brief Analyses of Previous Policy Work This appendix describes of some of the important problems with previous IETF policy work., and describes the rationale for taking different design decisions in this document. A.1. PolicySetComponent vs. SUPAPolicyStructure The ability to define different types of policy rules is not present in [RFC3060] and [RFC3460], because both are based on [4], and this ability is not present in [4]. [RFC3060], [RFC3460], and [4] are all limited to CA (condition-action) policy rules. In addition, events are NOT defined. These limitations mean that RFC3060], [RFC3460], and [4] can only represent CA Policy Rules. In contrast, the original design goal of SUPA was to define a single class hierarchy that could represent different types of policies (e.g., imperative and declarative). Hence, it was decided to make SUPAPolicyStructure generic in nature, so that different types of policies could be defined as subclasses. This enables a single Policy Framework to support multiple types of policies. A.2. Flat Hierarchy vs. SUPAPolicyComponentStructure Figure 32 shows a portion of the class hierarchy of [RFC3460]. A +--------+ | Policy | +----+---+ / \ | | +---------+------+------+------------+-----------+ | | | | | A | | A | | A | +-----+-----+ | +--------+--------+ | +------+-------+ | PolicySet | | | PolicyCondition | | | PolicyAction | +-----+-----| | +--------+--------+ | +------+-------+ / \ | / \ | / \ | | | | | ... | ... | ... A | A | +-------+--------+ +-------+-----+ | PolicyVariable | | PolicyValue | +-------+--------+ +-------+-----+ / \ / \ | | ... ... Figure 32. Simplified Class Hierarcy of [RFC3460] Strassner, et al. Expires November 30, 2017 [Page 134]
Internet-Draft SUPA Generic Policy Model May 2017 RFC3060], [RFC3460], and [4] defined PolicyConditions and PolicyActions as subclasses of Policy (along with PolicySet, which is the superclass of PolicyRules and PolicyGroups). This means that there is no commonality between PolicyConditions and PolicyActions, even though they are both PolicyRule components. From an object-oriented point-of-view, this is incorrect, since a PolicyRule aggregates both PolicyConditions and PolicyActions. In addition, note that both PolicyVariables and PolicyValues are siblings of PolicyRules, PolicyConditions, and PolicyActions. This is incorrect for several reasons: o a PolicyRule cannot rectly contain PolicyVariables or PolicyValues, so they shouldn't be at the same level of the class hierarchy o both PolicyConditions and PolicyActions can contain PolicyVariables and PolicyValues, which implies that both PolicyVariables and PolicyValues should be lower in the class hierarchy Note that in the current version of [4], PolicyVariable and PolicyValue are both deleted. There are other changes as well, but they are beyond the scope of this Appendix. The original design goal of SUPA was to define a single class hierarchy that could represent different types of policies and policy components. This cannot be accomplished in [RFC3460], since there is no notion of a policy component (or alternatively, PolicyCondition, PolicyAction, PolicyVariable, and PolicyValue are all components at the same abstraction level, which is clearly not correct). Hence, SUPA defined the SUPAPolicyComponentStructure class to capture the concept of a reusable policy component. In summary, SUPAPolicyStructure subclasses define the structure of a policy in a common way, while SUPAPolicyComponentStructure subclasses define the content that is contained in the structure of a policy, also in a common way. A.3. PolicyRules and PolicyGroups vs. SUPAPolicyRules A PolicySetComponent is an aggregation, implemented as an association class, that "collects instances of PolicySet subclasses into coherent sets of Policies". This is a recursive aggregation, with multiplicity 0..n - 0..n, on the PolicySet class. Since this is a recursive aggregation, it means that a PolicySet can aggregate zero or more PolicySets. This is under-specified, and can be interpreted in one of two ways: Strassner, et al. Expires November 30, 2017 [Page 135]
Internet-Draft SUPA Generic Policy Model May 2017 1. A PolicySet subclass can aggregate any PolicySet subclass (PolicyRules can aggregate PolicyRules and PolicyGroups, and vice-versa) 2. PolicyRules can aggregate PolicyRules, and PolicyGroups can aggregate PolicyGroups, but neither class can aggregate the other type of class Both interpretations are ill-suited for policy-based management. The problem with the first is that if PolicyGroup is the mechanism for grouping, why can a PolicyRule aggregate a PolicyGroup? This implies that PolicyGroups are not needed. The problem with the second is that PolicyGroups cannot aggregate PolicyRules (which again implies that PolicyGroups are not needed). Furthermore, there are no mechanisms defined in the [RFC3460] model to prevent loops of PolicyRules. This is a problem, because EVERY PolicyRule and PolicyGroup inherits this recursive aggregation. This is why this document uses the composite pattern. First, this pattern clearly shows what object is aggregating what other object (i.e., a SUPAECAPolicyRuleAtomic cannot aggregate a SUPAECAPolicyRuleComposite). Second, it does not allow a SUPAECAPolicyRule to be aggregated by another SUPAECAPolicyRule (this is discussed more in the following subsection). A.3.1. Sub-rules Sub-rules (also called nested policy rules) enable a policy rule to be contained within another policy rule. These have very complex semantics, are very hard to debug, and provide limited value. They also require a complex set of aggregations (see section A.4.). The main reason for defining sub-rules in [RFC3460] is to enable "complex policy rules to be constructed from multiple simpler policy rules". However, the composite pattern does this much more efficiently than a simple recursive aggregation, and avoids the ambiguous semantics of a recursive aggregation. This latter point is important, because if PolicyRule and/or PolicyGroup is subclassed, then all subclasses still inherit this recursive aggregation, along with its ambiguous semantics. A.4. PolicyConditions and PolicyActions vs. SUPAECAComponent There is no need to use the SimplePolicyCondition and ComplexPolicyCondition objects defined in [RFC3460], since the SUPAPolicyComponentStructure uses the decorator pattern (see section 5.7) to provide more extensible types of conditions than is possible with those classes. This also applies for the SimplePolicyAction and the ComplexPolicyAction classes defined in [RFC3460]. Strassner, et al. Expires November 30, 2017 [Page 136]
Internet-Draft SUPA Generic Policy Model May 2017 More importantly, this removes the need for a complex set of aggregations (i.e., PolicyComponent, PolicySetComponent, PolicyConditionStructure, PolicyConditionInPolicyRule, PolicyConditionInPolicyCondition, PolicyActionStructure, PolicyActionInPolicyRule, and PolicyActionInPolicyAction). Instead, ANY SUPAECAComponent is defined as a decorator (i.e., a subclass of SUPAPolicyComponentDecorator), and hence, Any SUPAECAComponent is wrapped onto a concrete subclass of SUPAPolicyClause using the SAME aggregation (SUPAHasDecoratedPolicyComponent). This is a significantly simpler design that is also more powerful. A.5. The SUPAPolicyComponentDecorator Abstraction One of the problems in building a policy model is the tendency to have a multitude of classes, and hence object instances, to represent different combinations of policy events, conditions, and actions. This can lead to class and/or relationship explosion, as is the case in [RFC3460], [4], and [6]. For example, [RFC3460] defines five subclasses of PolicyCondition: PolicyTimePeriodCondition, VendorPolicyCondition, SimplePolicyCondition, CompoundPolicyCondition, and CompoundFilterCondition. Of these: o PolicyTimePeriodCondition is a data structure, not a class o VendorPolicyCondition represents a condition using two attributes that represent a multi-valued octet string o SimplePolicyCondition, CompoundPolicyCondition, and CompoundFilterCondition all have ambiguous semantics SimplePolicyCondition represents an ordered 3-tuple, in the form {variable, match, value}. However, the match operator is not formally modeled. Specifically, "the 'match' relationship is to be interpreted by analyzing the variable and value instances associated with the simple condition". This becomes problematic for several cases, such as shallow vs. deep object comparisons. More importantly, this requires two separate aggregations (PolicyVariableInSimplePolicyCondition and PolicyValueInSimplePolicyCondition) to associate variables and values to the SimplePolicyCondition, respectively. Since [RFC3460] defines all relationships as classes, this means that the expression "Foo > Bar" requires a total of FIVE objects (one each for the variable and value, one for the SimplePolicyCondition, and one each to associate the variable and value with the SimplePolicyCondition). Strassner, et al. Expires November 30, 2017 [Page 137]
Internet-Draft SUPA Generic Policy Model May 2017 This is exacerbated when SimplePolicyConditions are used to build CompoundPolicyConditions. In addition to the above complexity (which is required for each SimplePolicyCondition), a new aggregation (PolicyConditionInPolicyCondition) is required to aggregation PolicyConditions. Thus, the compound expression: "((Foo > Bar) AND (Foo < Baz))" requires a total of THIRTEEN objects (five for each of the terms being ANDed, plus one for the CompoundPolicyCondition, and two to aggregate each term to the CompoundPolicyCondition). Note that in the above examples, the superclasses of each of the relationships are omitted for clarity. In addition, [RFC3460] is built using inheritance; this means that if a new function is required, a new class must be built (e.g., CompoundFilterCondition is a subclass, but all it adds is one attribute). In constrast, the Decorator Pattern enables behavior to be selectively added to an individual object, either statically or dynamically, without having to build association classes. In addition, the decorator pattern uses composition, instead of inheritance, to avoid class explosion. This means that a new variable, value, or even condition class can be defined at runtime, and then all or part of that class can dynamically wrap an existing object without need for recompilation and redeployment. A.6. The Abstract Class "SUPAPolicyClause" This abstraction is missing in [RFC3060], [RFC3460], [4], and [6]. SUPAPolicyClause was abstracted from DEN-ng [2], and a version of this class is in the process of being added to [5]. However, the class and relationship design in [5] differs significantly from the corresponding designs in this document. SUPAPolicyClause further reinforces the different between a policy rule and a component of a policy rule by abstracting the content of a policy rule as a reusable object. This is fundamental for enabling different types of policy rules (e.g., imperative and declarative) to to be represented using the same constructs. A.7. Problems with the RFC3460 Version of PolicyVariable The following subsections define a brief, and incomplete, set of problems with the implementation of [RFC3460] (note that [RFC3060 did not define variables, operators, and/or values). A.7.1. Object Bloat [RFC3460] used two different and complex mechanisms for providing generic get and set expressions. PolicyVariables were subclassed into two subclasses, even though they performed the same semantic function. This causes additional problems: Strassner, et al. Expires November 30, 2017 [Page 138]
Internet-Draft SUPA Generic Policy Model May 2017 o PolicyExplicitVariables are for CIM compatibility; note that the CIM does not contain either PolicyVariables or PolicyValues ([4]) o PolicyImplicitVariable subclasses do not define attributes; rather, they are bound to an appropriate subclass of PolicyValue using an association Hence, defining a variable is relatively expensive in [RFC3460], as in general, two objects and an association must be used. The objects themselves do not define content; rather, their names are used as a mechanism to identify an object to match. This means that an entire object must be used (instead of, for example, an attribute), which is wasteful. It also make it difficult to adjust constraints at runtime, since the constraint is defined in a class that is statically defined (and hence, requires recompilation and possibly redeployment if it is changed). A.7.2. Object Explosion The above three problems lead to class explosion (recall that in [RFC3060], [RFC3460], and [4], associations are implemented as classes). In contrast to this approach, the approach in this document keeps the idea of the class hierarchy for backwards compatibility, but streamlines the implementation. Specifically: 1. The decorator pattern is an established and very used software pattern (it dates back to at least 1994 [11]). 2. The use of a single association class (i.e., SUPAHasDecoratedPolicyComponentDetail) can represent more constraints than is possible in the approaches of [RFC3460] and [4] in a much more flexible manner, due to its function as a decorator of other objects. 3. Note that there is no way to enforce the constraint matching in [RFC3460] and [6]; the burden is on the developer to check and see if the constraints specified in one class are honored in the other class. 4. If these constraints are not honored, there is no mechanism specified to define the clause as incorrectly formed. A.7.3. Specification Ambiguities There are a number of ambiguities in [RFC3460]. First, [RFC3460] says: "Variables are used for building individual conditions". While this is true, variables can also be used for building individual actions. This is reflected in the definition for SUPAPolicyVariable. Strassner, et al. Expires November 30, 2017 [Page 139]
Internet-Draft SUPA Generic Policy Model May 2017 Second, [RFC3460] says: "The variable specifies the property of a flow or an event that should be matched when evaluating the condition." While this is true, variables can be used to test many other things than "just" a flow or an event. This is reflected in the SUPAPolicyVariable definition. Third, the [RFC3460] definition requires the use of associations in order to properly constrain the variable (e.g., define its data type, the range of its allowed values, etc.). This is both costly and inefficient. Fourth, [RFC3460] is tightly bound to the DMTF CIM schema [4]. The CIM is a data model (despite its name), because: o It uses keys and weak relationships, which are both concepts from relational algebra and thus, not technology-independent o It has its own proprietary modeling language o It contains a number of concepts that are not defined in UML (including overriding keys for subclasses) Fifth, the class hierarchy has two needless classes, called SUPAImplicitVariable and SUPAExplicitVariable. These classes do not define any attributes or relationships, and hence, do not add any semantics to the model. Finally, in [RFC3460], defining constraints for a variable is limited to associating the variable with a PolicyValue. This is both cumbersome (because associations are costly; for example, they equate to a join in a relational database management system), and not scalable, because it is prone to proliferating PolicyValue classes for every constraint (or range of constraints) that is possible. Therefore, in SUPA, this mechanism is replaced with using an association to an association class that defines constraints in a much more general and powerful manner (i.e., the SUPAHasDecoratedPolicyComponentDetail class). A.8. Problems with the RFC3460 Version of PolicyValue The following subsections define a brief, and incomplete, set of problems with the implementation of [RFC3460] (note that [RFC3060 did not define variables, operators, and/or values). A.8.1. Object Bloat [RFC3460] defined a set of 7 subclasses; three were specific to networking (i.e., IPv4 Address, IPv6 Address, MAC Address) and 4 (PolicyStringValue, PolicyBitStringValue, PolicyIntegerValue, and PolicyBooleanValue) were generic in nature. However, each of these objects defined a single class attribute. This has the same two problems as with PolicyVariables (see section 5.9.1.1): Strassner, et al. Expires November 30, 2017 [Page 140]
Internet-Draft SUPA Generic Policy Model May 2017 1. Using an entire object to define a single attribute is very wasteful and expensive 2. It also make it difficult to adjust constraints at runtime, since the constraint is defined in a class that is statically defined (and hence, requires recompilation and possibly redeployment if it is changed). A.8.2. Object Explosion [RFC3460] definition requires the use of associations in order to properly constrain the variable (e.g., define its data type, the range of its allowed values, etc.). This is both costly and inefficient (recall that in [RFC3060], [RFC3460], and [4], associations are implemented as classes). A.8.3. Lack of Constraints There is no generic facility for defining constraints for a PolicyValue. Therefore, there is no facility for being able to change such constraints dynamically at runtime. A.8.4. Tightly Bound to the CIM Schema [RFC3460] is tightly bound to the DMTF CIM schema [4]. The CIM is a data model (despite its name), because: o It uses keys and weak relationships, which are both concepts from relational algebra and thus, not technology-independent o It has its own proprietary modeling language o It contains a number of concepts that are not defined in UML (including overriding keys for subclasses) A.8.5. Specification Ambiguity [RFC3460] says: It is used for defining values and constants used in policy conditions". While this is true, variables can also be used for building individual actions. This is reflected in the SUPAPolicyVariable definition. A.8.6. Lack of Symmetry Most good information models show symmetry between like components. [RFC3460] has no symmetry in how it defines variables and values. In contrast, this document recognizes that variables and values are just terms in a clause; hence, the only difference in the definition of the SUPAPolicyVariable and SUPAPolicyValue classes is that the content attribute in the former is a single string, whereas the content attribute in the latter is a string array. In particular, the semantics of both variables and values are defined using the decorator pattern, along with the attributes of the SUPAPolicyComponentDecorator and the SUPAHasDecoratedPolicyComponentDetail classes. Strassner, et al. Expires November 30, 2017 [Page 141]