Policy Framework Working Group                                 B. Moore
 INTERNET-DRAFT                                              E. Ellesson
 Category: Standards Track                                           IBM
                                                             J. Strassner
                                                            A. Westerinen
                                                            Cisco Systems
                                                               July, 2000
 
 
 
 
          Policy Core Information Model -- Version 1 Specification
 
                 <draft-ietf-policy-core-info-model-07.txt>
                       Friday, July 14, 2000, 1:33 PM
 
 Status of this Memo
 
   This document is an Internet-Draft and is in full conformance with all
   provisions of Section 10 of RFC2026.
 
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 Copyright Notice
 
   Copyright (C) The Internet Society (2000).  All Rights Reserved.
 
 Abstract
 
   This document presents the object-oriented information model for
   representing policy information developed jointly in the IETF Policy
   Framework WG and as extensions to the Common Information Model (CIM)
   activity in the Distributed Management Task Force (DMTF).  This model
   defines two hierarchies of object classes:  structural classes
   representing policy information and control of policies, and
   association classes that indicate how instances of the structural
   classes are related to each other. Subsequent documents will define
   mappings of this information model to various concrete
   implementations, for example, to a directory that uses LDAPv3 as its
   access protocol.  The components of the CIM schema are available via
   the following URL:  http://www.dmtf.org/spec/cims.html [1].
 
 
 
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   Table of Contents
 
   1. Introduction......................................................4
   2. Modeling Policies.................................................5
      2.1. Policy Scope.................................................7
      2.2. Declarative versus Procedural Model..........................8
   3. Overview of the Policy Core Information Model.....................9
   4. Inheritance Hierarchies for the Policy Core Information Model....12
   5. Details of the Model.............................................13
      5.1. Reusable versus Rule-Specific Conditions and Actions........13
      5.2. Roles.......................................................15
      5.2.1. Roles and Role Combinations...............................15
      5.2.2. The PolicyRoles Property..................................18
      5.3. Local Time and UTC Time in PolicyTimePeriodConditions.......18
      5.4. CIM Data Types..............................................20
   6. Class Definitions................................................20
      6.1. The Abstract Class "Policy".................................21
      6.1.1. The Property "CommonName (CN)"............................22
      6.1.2. The Multi-valued Property "PolicyKeywords"................22
      6.1.3. The Property "Caption" (Inherited from ManagedElement)....23
      6.1.4. The Property "Description" (Inherited from ManagedElement)23
      6.2. The Class "PolicyGroup".....................................23
      6.3. The Class "PolicyRule"......................................24
      6.3.1. The Property "Enabled"....................................26
      6.3.2. The Property "ConditionListType"..........................26
      6.3.3. The Property "RuleUsage"..................................27
      6.3.4. The Property "Priority"...................................27
      6.3.5. The Property "Mandatory"..................................27
      6.3.6. The Property "SequencedActions"...........................28
      6.3.7. The Multi-valued Property "PolicyRoles"...................28
      6.4. The Class "PolicyCondition".................................29
      6.5. The Class "PolicyTimePeriodCondition".......................31
      6.5.1. The Property "TimePeriod".................................32
      6.5.2. The Property "MonthOfYearMask"............................33
      6.5.3. The Property "DayOfMonthMask".............................34
      6.5.4. The Property "DayOfWeekMask"..............................35
      6.5.5. The Property "TimeOfDayMask"..............................35
      6.5.6. The Property "LocalOrUtcTime".............................36
      6.6. The Class "VendorPolicyCondition"...........................36
      6.6.1. The Multi-valued Property "Constraint"....................37
      6.6.2. The Property "ConstraintEncoding".........................38
      6.7. The Class "PolicyAction"....................................38
      6.8. The Class "VendorPolicyAction"..............................39
      6.8.1. The Multi-valued Property "ActionData"....................39
      6.8.2. The Property "ActionEncoding".............................40
      6.9. The Class "PolicyRepository"................................40
   7. Association and Aggregation Definitions..........................41
      7.1. Associations................................................41
      7.2. Aggregations................................................41
      7.3. The Abstract Aggregation "PolicyComponent...................41
      7.4. The Aggregation "PolicyGroupInPolicyGroup"..................41
      7.4.1. The Reference "GroupComponent"............................42
      7.4.2. The Reference "PartComponent".............................42
 
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      7.5. The Aggregation "PolicyRuleInPolicyGroup"...................42
      7.5.1. The Reference "GroupComponent"............................43
      7.5.2. The Reference "PartComponent".............................43
      7.6. The Aggregation "PolicyConditionInPolicyRule"...............43
      7.6.1. The Reference "GroupComponent"............................44
      7.6.2. The Reference "PartComponent".............................44
      7.6.3. The Property "GroupNumber"................................44
      7.6.4. The Property "ConditionNegated"...........................44
      7.7. The Aggregation "PolicyRuleValidityPeriod"..................45
      7.7.1. The Reference "GroupComponent"............................45
      7.7.2. The Reference "PartComponent".............................45
      7.8. The Aggregation "PolicyActionInPolicyRule"..................46
      7.8.1. The Reference "GroupComponent"............................46
      7.8.2. The Reference "PartComponent".............................46
      7.8.3. The Property "ActionOrder"................................47
      7.9. The Abstract Association "PolicyInSystem"...................48
      7.10. The Weak Association "PolicyGroupInSystem".................48
      7.10.1. The Reference "Antecedent"...............................48
      7.10.2. The Reference "Dependent"................................49
      7.11. The Weak Association "PolicyRuleInSystem"..................49
      7.11.1. The Reference "Antecedent"...............................49
      7.11.2. The Reference "Dependent"................................49
      7.12. The Association "PolicyConditionInPolicyRepository"........49
      7.12.1. The Reference "Antecedent"...............................50
      7.12.2. The Reference "Dependent"................................50
      7.13. The Association "PolicyActionInPolicyRepository"...........50
      7.13.1. The Reference "Antecedent"...............................50
      7.13.2. The Reference "Dependent"................................51
      7.14. The Aggregation "PolicyRepositoryInPolicyRepository".......51
      7.14.1. The Reference "GroupComponent"...........................51
      7.14.2. The Reference "PartComponent"............................51
   8. Intellectual Property............................................52
   9. Acknowledgements.................................................52
   10. Security Considerations.........................................52
   11. References......................................................54
   12. Authors' Addresses..............................................55
   13. Full Copyright Statement........................................56
   14. Appendix A - Class Identification in a Native CIM Implementation57
      14.1. Naming Instances of PolicyGroup and PolicyRule.............57
      14.1.1. PolicyGroup's CIM Keys...................................57
      14.1.2. PolicyRule's CIM Keys....................................58
      14.2. Naming Instances of PolicyCondition and Its Subclasses.....59
      14.2.1. PolicyCondition's CIM Keys...............................61
      14.3. Naming Instances of PolicyAction and Its Subclasses........62
      14.4. Naming Instances of PolicyRepository.......................64
      14.5. Role of the CreationClassName Property in Naming...........64
      14.6. Object References..........................................65
 
 
 
 
 
 
 
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 1. Introduction
 
   This document presents the object-oriented information model for
   representing policy information currently under joint development in
   the IETF Policy Framework WG and as extensions to the Common
   Information Model (CIM) activity in the Distributed Management Task
   Force (DMTF).  This model defines two hierarchies of object classes:
   structural classes representing policy information and control of
   policies, and association classes that indicate how instances of the
   structural classes are related to each other. Subsequent documents
   will define mappings of this information model to various concrete
   implementations, for example, to a directory that uses LDAPv3 as its
   access protocol.
 
   The policy classes and associations defined in this model are
   sufficiently generic to allow them to represent policies related to
   anything.  However, it is expected that their initial application in
   the IETF will be for representing policies related to QoS (DiffServ
   and IntServ) and to IPSec.  Policy models for application-specific
   areas such as these may extend the Core Model in several ways.  The
   preferred way is to use the PolicyGroup, PolicyRule, and
   PolicyTimePeriodCondition classes directly, as a foundation for
   representing and communicating policy information.  Then, specific
   subclasses derived from PolicyCondition and PolicyAction can capture
   application-specific definitions of conditions and actions of
   policies.
 
   Two subclasses, VendorPolicyCondition and VendorPolicyAction, are also
   included in this document, to provide a standard extension mechanism
   for vendor-specific extensions to the Policy Core Information Model.
 
   This document fits into the overall framework for representing,
   deploying, and managing policies being developed by the Policy
   Framework Working Group.  It traces its origins to work that was
   originally done for the Directory-enabled Networks (DEN)
   specification, reference [5].  Work on the DEN specification by the
   DEN Ad-Hoc Working Group itself has been completed.  Further work to
   standardize the models contained in it will be the responsibility of
   selected working groups of the CIM effort in the Distributed
   Management Task Force (DMTF).  DMTF standardization of the core policy
   model is the responsibility of the SLA Policy working group in the
   DMTF.
 
   This document is organized in the following manner:
 
   o  Section 2 provides a general overview of policies and how they are
      modeled.
 
   o  Section 3 presents a high-level overview of the classes and
      associations comprising the Policy Core Information Model.
 
   o  The remainder of the document presents the detailed specifications
      for each of the classes and associations.
 
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   o  Appendix A overviews naming for native CIM implementations.  Other
      mappings, such as LDAPv3, will have their own naming mechanisms.
 
   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 RFC 2119, reference
   [3].
 
 
 2. Modeling Policies
 
   The classes comprising the Policy Core Information Model are intended
   to serve as an extensible class hierarchy (through specialization) for
   defining policy objects that enable application developers, network
   administrators, and policy administrators to represent policies of
   different types.
 
   One way to think of a policy-controlled network is to first model the
   network as a state machine and then use policy to control which state
   a policy-controlled device should be in or is allowed to be in at any
   given time.  Given this approach, policy is applied using a set of
   policy rules.  Each policy rule consists of a set of conditions and a
   set of actions.  Policy rules may be aggregated into policy groups.
   These groups may be nested, to represent a hierarchy of policies.
 
   The set of conditions associated with a policy rule specifies when the
   policy rule is applicable.  The set of conditions can be expressed as
   either an ORed set of ANDed sets of condition statements or an ANDed
   set of ORed sets of statements.  Individual condition statements can
   also be negated.  These combinations are termed, respectively,
   Disjunctive Normal Form (DNF) and Conjunctive Normal Form (CNF) for
   the conditions.
 
   If the set of conditions associated with a policy rule evaluates to
   TRUE, then a set of actions that either maintain the current state of
   the object or transition the object to a new state may be executed.
   For the set of actions associated with a policy rule, it is possible
   to specify an order of execution, as well as an indication of whether
   the order is required or merely recommended.  It is also possible to
   indicate that the order in which the actions are executed does not
   matter.
 
   Policy rules themselves can be prioritized.  One common reason for
   doing this is to express an overall policy that has a general case
   with a few specific exceptions.
 
   For example, a general QoS policy rule might specify that traffic
   originating from members of the engineering group is to get Bronze
   Service.  A second policy rule might express an exception: traffic
   originating from John, a specific member of the engineering group, is
   to get Gold Service.  Since traffic originating from John satisfies
   the conditions of both policy rules, and since the actions associated
   with the two rules are incompatible, a priority needs to be
 
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   established.  By giving the second rule (the exception) a higher
   priority than the first rule (the general case), a policy
   administrator can get the desired effect: traffic originating from
   John gets Gold Service, and traffic originating from all the other
   members of the engineering group gets Bronze Service.
 
   Policies can either be used in a stand-alone fashion or aggregated
   into policy groups to perform more elaborate functions. Stand-alone
   policies are called policy rules. Policy groups are aggregations of
   policy rules, or aggregations of policy groups, but not both. Policy
   groups can model intricate interactions between objects that have
   complex interdependencies. Examples of this include a sophisticated
   user logon policy that sets up application access, security, and
   reconfigures network connections based on a combination of user
   identity, network location, logon method and time of day. A policy
   group represents a unit of reusability and manageability in that its
   management is handled by an identifiable group of administrators and
   its policy rules would be consistently applied
 
   Stand-alone policies are those that can be expressed in a simple
   statement. They can be represented effectively in schemata or MIBs.
   Examples of this are VLAN assignments, simple YES/NO QoS requests, and
   IP address allocations. A specific design goal of this model is to
   support both stand-alone and aggregated policies.
 
   Policy groups and rules can be classified by their purpose and intent.
   This classification is useful in querying or grouping policy rules.
   It indicates whether the policy is used to motivate when or how an
   action occurs, or to characterize services (that can then be used, for
   example, to bind clients to network services).  Describing each of
   these concepts in more detail,
 
   o Motivational Policies are solely targeted at whether or how a
     policy's goal is accomplished.  Configuration and Usage Policies
     are specific kinds of Motivational Policies.  Another example is
     the scheduling of file backup based on disk write activity from 8am
     to 3pm, M-F.
 
   o Configuration Policies define the default (or generic) setup of a
     managed entity (for example, a network service).  Examples of
     Configuration Policies are the setup of a network forwarding
     service or a network-hosted print queue.
 
   o Installation Policies define what can and cannot be put on a system
     or component, as well as the configuration of the mechanisms that
     perform the install. Installation policies typically represent
     specific administrative permissions, and can also represent
     dependencies between different components (e.g., to complete the
     installation of component A, components B and C must be previously
     successfully installed or uninstalled).
 
 
 
 
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   o Error and Event Policies. For example, if a device fails between
     8am and 9pm, call the system administrator, otherwise call the Help
     Desk.
 
   o Usage Policies control the selection and configuration of entities
     based on specific "usage" data.  Configuration Policies can be
     modified or simply re-applied by Usage Policies.  Examples of Usage
     Policies include upgrading network forwarding services after a user
     is verified to be a member of a "gold" service group, or
     reconfiguring a printer to be able to handle the next job in its
     queue.
 
   o Security Policies deal with verifying that the client is actually
     who the client purports to be, permitting or denying access to
     resources, selecting and applying appropriate authentication
     mechanisms, and performing accounting and auditing of resources.
 
   o Service Policies characterize network and other services (not use
     them). For example, all wide-area backbone interfaces shall use a
     specific type of queuing.
 
     Service policies describe services available in the network. Usage
     policies describe the particular binding of a client of the network
     to services available in the network.
 
   These categories are represented in the Policy Core Information Model
   by special values defined for the PolicyKeywords property of the
   abstract class Policy.
 
 2.1. Policy Scope
 
   Policies represent business goals and objectives.  A translation must
   be made between these goals and objectives and their realization in
   the network. An example of this could be a Service Level Agreement
   (SLA), and its objectives and metrics (Service Level Objectives, or
   SLOs), that are used to specify services that the network will provide
   for a given client.  The SLA will usually be written in high-level
   business terminology. SLOs address more specific metrics in support of
   the SLA. These high-level descriptions of network services and metrics
   must be translated into lower-level, but also vendor- and device-
   independent specifications. The Policy Core Information Model classes
   are intended to serve as the foundation for these lower-level, vendor-
   and device-independent specifications.
 
   It is envisioned that the definition of the Policy Core Informational
   Model in this draft is generic in nature and is applicable to Quality
   of Service (QoS), to non-QoS networking applications (e.g., DHCP and
   IPSec), and to non-networking applications (e.g., backup policies,
   auditing access, etc.).
 
 
 
 
 
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 2.2. Declarative versus Procedural Model
 
   The design of the Policy Core Information Model is influenced by a
   declarative, not procedural, approach. More formally, a declarative
   language is used to describe relational and functional languages.
   Declarative languages describe relationships between variables in
   terms of functions or inference rules, to which the interpreter or
   compiler can apply a fixed algorithm in order to produce a result. An
   imperative (or procedural) language specifies an explicit sequence of
   steps to follow in order to produce a result.
 
   It is important to note that this information model does not rule out
   the use of procedural languages. Rather, it recognizes that both
   declarative as well as procedural languages can be used to implement
   policy. This information model is better viewed as being declarative
   because the sequence of steps for doing the processing of declarative
   statements tends to be left to the implementer. However, we have
   provided the option of expressing the desired order of action
   execution in this policy information model, and for expressing whether
   the order is mandatory or not. In addition, rather than trying to
   define algorithms or sets of instructions or steps that must be
   followed by a policy rule, we instead define a set of modular building
   blocks and relationships that can be used in a declarative or
   procedural fashion to define policies.
 
   Compare this to a strictly procedural model. Taking such an approach
   would require that we specify the condition testing sequence, and the
   action execution sequence, in the policy repository itself. This
   would, indeed, constrain the implementer. This is why the policy model
   is characterized as a declarative one. That is, the information model
   defines a set of attributes, and a set of entities that contain these
   attributes. However, it does NOT define either the algorithm to
   produce a result using the attributes or an explicit sequence of steps
   to produce a result.
 
   There are several design considerations and trade-offs to make in this
   respect.
 
  1.  On the one hand, we would like a policy definition language to be
      reasonably human-friendly for ease of definitions and diagnostics.
      On the other hand, given the diversity of devices (in terms of
      their processing capabilities) which could act as policy decision
      points, we would like to keep the language somewhat machine-
      friendly. That is, it should be relatively simple to automate the
      parsing and processing of the language in network elements. The
      approach taken is to provide a set of classes and attributes that
      can be combined in either a declarative or procedural approach to
      express policies that manage network elements and services. The key
      point is to avoid trying to standardize rules or sets of steps to
      be followed in defining a policy. These must be left up to an
      implementation. Interoperability is achieved by standardizing the
      building blocks that are used to represent policy data and
      information.
 
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  2.  An important decision to make is the semantic style of the
      representation of the information.
 
      The declarative approach that we are describing falls short of
      being a "true" declarative model. Such a model would also specify
      the algorithms used to combine the information and policy rules to
      achieve particular behavior. We avoid specifying algorithms for the
      same reason that we avoid specifying sets of steps to be followed
      in a policy rule. However, the design of the information model more
      closely follows that of a declarative language, and may be easier
      to understand if such a conceptual model is used. This leads to our
      third point, acknowledging a lack of "completeness" and instead
      relying on presenting information that the policy processing entity
      will work with.
 
  3.  It is important to control the complexity of the specification,
      trading off richness of expression of data in the core information
      model for ease of implementation and use. It is important to
      acknowledge the collective lack of experience in the field
      regarding policies to control and manage network services and
      hence avoid the temptation of aiming for "completeness". We should
      instead strive to facilitate definition of a set of common policies
      that customers require today (e.g., VPN and QoS) and allow
      migration paths towards supporting complex policies as customer
      needs and our understanding of these policies evolve with
      experience. Specifically, in the context of the declarative style
      language discussed above, it is important to avoid having full
      blown predicate calculus as the language, as it would render many
      important problems such as consistency checking and policy decision
      point algorithms intractable. It is useful to consider a reasonably
      constrained language from these perspectives.
 
 
  The Policy Core Information Model strikes a balance between complexity
  and lack of power by using the well understood logical concepts of
  Disjunctive Normal Form and Conjunctive Normal Form for combining
  simple policy conditions into more complex ones.
 
 
 3. Overview of the Policy Core Information Model
 
   The following diagram provides an overview of the five central classes
   comprising the Policy Core Information Model, their associations to
   each other, and their associations to other classes in the overall CIM
   model.  Note that the abstract class Policy and the two extension
   classes VendorPolicyCondition and VendorPolicyAction are not shown.
 
   NOTE:  For cardinalities, "*" is an abbreviation for "0..n".
 
 
 
 
 
 
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                                  +-----------+
                                  |  System   |
               .....              +--^-----^--+       .....
               .   .                1.    1.          .   .
              *.(a).*                .(b)  .(c)      *.(d).*
            +--v---v---------+       .     .        +-v---v------------+
            |  PolicyGroup   <........     .        | PolicyRepository |
            |                | w *         .        |                  |
            +------^---------+             .        +-----^---------^--+
                  *.                       .         0..1 .    0..1 .
                   .(e)                    .              .(f)      .(g)
                  *.                       .              .         .
            +------v------+ w *            .              .         .
            |             <.................              .         .
            | PolicyRule  |                               .         .
            |             |                               .         .
            |             |                               .         .
            |             <........................       .         .
            |             |*      (h)             .       .         .
            |             |                       .       .         .
            |             |                       .       .         .
            |             |                       .       .         .
            |             |                       .       .         .
            |             |                       .       .         .
            |             |                       .       .         .
            |             |                       .*      .*        .
            |             |             +---------v-------v--+      .
            |             |             |  PolicyCondition   |      .
            |             |            *+--------------------+      .
            |             |       (i)             ^                 .
            |             <..............         I                 .
            |             |*            .         I                 .
            |             |             .*        ^                 .
            |             |        +----v----------------------+    .
            |             |        | PolicyTimePeriodCondition |    .
            |             |        +---------------------------+    .
            |             |       (j)                               .
            |             <.........................                .
            |             |*                       .                .
            |             |                        .*               .
            |             |             +----------v---------+*     .
            |             |             | PolicyAction       <.......
            +-------------+             +--------------------+
 
   Figure 1.    Overview of the Core Policy Classes and Relationships
 
   In this figure the boxes represent the classes, and the dotted arrows
   represent the associations.  The following associations appear:
 
   (a)     PolicyGroupInPolicyGroup
 
   (b)     PolicyGroupInSystem
 
 
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   (c)     PolicyRuleInSystem
 
   (d)     PolicyRepositoryInPolicyRepository
 
   (e)     PolicyRuleInPolicyGroup
 
   (f)     PolicyConditionInPolicyRepository
 
   (g)     PolicyActionInPolicyRepository
 
   (h)     PolicyConditionInPolicyRule
 
   (i)     PolicyRuleValidityPeriod
 
   (j)     PolicyActionInPolicyRule
 
   An association always connects two classes.  The "two" classes may,
   however, be the same class, as is the case with the
   PolicyGroupInPolicyGroup association, which represents the recursive
   containment of PolicyGroups in other PolicyGroups.  The
   PolicyRepositoryInPolicyRepository association is recursive in the
   same way.
 
   An association includes cardinalities for each of the related classes.
   These cardinalities indicate how many instances of each class may be
   related to an instance of the other class.  For example, the
   PolicyRuleInPolicyGroup association has the cardinality range "*'
   (that is, "0..n") for both the PolicyGroup and PolicyRule classes.
   These ranges are interpreted as follows:
 
   o The "*" written next to PolicyGroup indicates that a PolicyRule may
     be related to no PolicyGroups, to one PolicyGroup, or to more than
     one PolicyGroup via the PolicyGroupInPolicyGroup association.  In
     other words, a PolicyRule may be contained in no PolicyGroups, in
     one PolicyGroups, or in more than one PolicyGroup.
 
   o The "*" written next to PolicyRule indicates that a PolicyGroup may
     be related to no PolicyRules, to one PolicyRule, or to more than
     one PolicyRule via the PolicyGroupInPolicyGroup association.  In
     other words, a PolicyGroup may contain no PolicyRules, one
     PolicyRule, or more than one PolicyRule.
 
   The "w" written next to the PolicyGroupInSystem and PolicyRuleInSystem
   indicates that these are what CIM terms "aggregations with weak
   references", or more briefly, "weak aggregations."   A weak
   aggregation is simply an indication of a naming scope.  Thus these two
   aggregations indicate that an instance of a PolicyGroup or PolicyRule
   is named within the scope of a System object.  A weak aggregation
   implicitly has the cardinality 1..1 at the end opposite the 'w'.
 
   The associations shown in Figure 1 are discussed in more detail in
   Section 7.
 
 
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 4. Inheritance Hierarchies for the Policy Core Information Model
 
   The following diagram illustrates the inheritance hierarchy for the
   core policy classes:
 
     ManagedElement (abstract)
      |
      +--Policy (abstract)
      |  |
      |  +---PolicyGroup
      |  |
      |  +---PolicyRule
      |  |
      |  +---PolicyCondition
      |  |          |
      |  |          +---PolicyTimePeriodCondition
      |  |          |
      |  |          +---VendorPolicyCondition
      |  |
      |  +---PolicyAction
      |             |
      |             +---VendorPolicyAction
      |
      +--ManagedSystemElement (abstract)
         |
         +--LogicalElement (abstract)
            |
            +--System (abstract)
               |
               +--AdminDomain (abstract)
                  |
                  +---PolicyRepository
 
 
   Figure 2.    Inheritance Hierarchy for the Core Policy Classes
 
   ManagedElement, as well as the four additional CIM classes from which
   PolicyRepository is derived, are defined in the CIM schema [1].  These
   classes are not discussed in detail in this document.
 
   In CIM, associations are also modeled as classes.  For the Policy Core
   Information Model, the inheritance hierarchy for the associations is
   as follows:
 
 
 
 
 
 
 
 
 
 
 
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     [unrooted]
      |
      +---PolicyComponent (abstract)
      |   |
      |   +---PolicyGroupInPolicyGroup
      |   |
      |   +---PolicyRuleInPolicyGroup
      |   |
      |   +---PolicyConditionInPolicyRule
      |   |
      |   +---PolicyRuleValidityPeriod
      |   |
      |   +---PolicyActionInPolicyRule
      |
      +---Dependency (abstract)
      |   |
      |   +---PolicyInSystem (abstract)
      |       |
      |       +---PolicyGroupInSystem
      |       |
      |       +---PolicyRuleInSystem
      |       |
      |       +---PolicyConditionInPolicyRepository
      |       |
      |       +---PolicyActionInPolicyRepository
      |
      +---Component (abstract)
          |
          +---SystemComponent
              |
              +---PolicyRepositoryInPolicyRepository
 
 
   Figure 3.    Inheritance Hierarchy for the Core Policy Associations
 
 
 5. Details of the Model
 
   The following subsections discuss several specific issues related to
   the Policy Core Information Model.
 
 5.1. Reusable versus Rule-Specific Conditions and Actions
 
   Policy conditions and policy actions can be partitioned into two
   groups:  ones associated with a single policy rule, and ones that are
   reusable, in the sense that they may be associated with more than one
   policy rule.  Conditions and actions in the first group are termed
   "rule-specific" conditions and actions; those in the second group are
   characterized as "reusable".
 
   It is important to understand that the difference between a rule-
   specific condition or action and a reusable one is based on the intent
   of the policy administrator for the condition or action, rather than
 
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   on the current associations in which the condition or action
   participates.  Thus a reusable condition or action (that is, one that
   a policy administrator has created to be reusable) may at some point
   in time be associated with exactly one policy rule, without thereby
   becoming rule-specific.
 
   There is no inherent difference between a rule-specific condition or
   action and a reusable one.  There are, however, differences in how
   they are treated in a policy repository.  For example, it's natural to
   make the access permissions for a rule-specific condition or action
   identical to those for the rule itself.  It's also natural for a rule-
   specific condition or action to be removed from the policy repository
   at the same time the rule is.  With reusable conditions and actions,
   on the other hand, access permissions and existence criteria must be
   expressible without reference to a policy rule.
 
   The preceding paragraph does not contain an exhaustive list of the
   ways in which reusable and rule-specific conditions should be treated
   differently.  Its purpose is merely to justify making a semantic
   distinction between rule-specific and reusable, and then reflecting
   this distinction in the policy model itself.
 
   An issue is highlighted by reusable and rule-specific policy
   conditions and policy actions:  the lack of a programmatic capability
   for expressing complex constraints involving multiple associations.
   Taking PolicyCondition as an example, there are two aggregations to
   look at.  PolicyConditionInPolicyRule has the cardinality * at both
   ends, and PolicyConditionInPolicyRepository has the cardinality * at
   the PolicyCondition end, and [0..1] at the PolicyRepository end.
 
   Globally, these cardinalities are correct.  However, there's more to
   the story, which only becomes clear if we examine the cardinalities
   separately for the two cases of a rule-specific PolicyCondition and a
   reusable one.
 
   For a rule-specific PolicyCondition, the cardinality of
   PolicyConditionInPolicyRule at the PolicyRule end is [1..1], rather
   than [0..n] (recall that * is an abbreviation for [0..n]), since the
   condition is unique to one policy rule.  And the cardinality of
   PolicyConditionInPolicyRepository at the PolicyRepository end is
   [0..0], since the condition is not in the "re-usable" repository.
   This is OK, since these are both subsets of the specified
   cardinalities.
 
   For a reusable PolicyCondition, however, the cardinality of
   PolicyConditionInPolicyRepository at the PolicyRepository end is
   [1..1], since the condition must be in the repository. And, the
   cardinality of PolicyConditionInPolicyRule at the PolicyRule end is
   [0..n].  This last point is important:  a reusable PolicyCondition may
   be associated with 0, 1, or more than 1 PolicyRules, via exactly the
   same association PolicyConditionInPolicyRule that binds a rule-
   specific condition to its PolicyRule.
 
 
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   Currently the only way to document constraints of this type is
   textually.  More formal methods for documenting complex constraints
   are needed.
 
 5.2. Roles
 
 5.2.1. Roles and Role Combinations
 
   The concept of role is central to the design of the entire Policy
   Framework.  The idea behind roles is a simple one.  Rather than
   configuring, and then later having to update the configuration of,
   hundreds or thousands (or more) of resources in a network, a policy
   administrator assigns each resource to one or more roles, and then
   specifies the policies for each of these roles.  The Policy Framework
   is then responsible for configuring each of the resources associated
   with a role in such a way that it behaves according to the policies
   specified for that role.  When network behavior must be changed, the
   policy administrator can perform a single update to the policy for a
   role, and the Policy Framework will ensure that the necessary
   configuration updates are performed on all the resources playing that
   role.
 
   A more formal definition of a role is as follows:
 
      A role is a type of attribute that is used to select one or more
      policies for a set of entities and/or components from among a much
      larger set of available policies.
 
   Roles can be combined together.  Here is a formal definition of a
   "role-combination":
 
      A role-combination is a set of attributes that are used to select
      one or more policies for a set of entities and/or components from
      among a much larger set of available policies.  As the examples
      below illustrate, the selection process for a role combination
      chooses policies associated with the combination itself, policies
      associated with each of its sub-combinations, and policies
      associated with each of the individual roles in the role-
      combination.
 
   It is important to note that a role is more than an attribute. A role
   defines a particular function of an entity or component that can be
   used to identify particular behavior associated with that entity or
   component. This difference is critical, and is most easily understood
   by thinking of a role as a selector. When used in this manner, one
   role (or role-combination) selects a different set of policies than a
   different role (or role-combination) does.
 
   Roles and role-combinations are especially useful in selecting which
   policies are applicable to a particular set of entities or components
   when the policy repository can store thousands or hundreds of
   thousands of policies. This use emphasizes the ability of the role (or
 
 
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   role-combination) to select the small subset of policies that are
   applicable from a huge set of policies that are available.
 
   An example will illustrate how role-combinations actually work.
   Suppose an installation has three roles defined for interfaces:
   "Ethernet", "Campus", and "WAN".  In the Policy Repository, some
   policy rules could be associated with the role "Ethernet"; these rules
   would apply to all Ethernet interfaces, regardless of whether they
   were on the campus side or the WAN side.  Other rules could be
   associated with the role-combination "Campus"+"Ethernet"; these rules
   would apply to the campus-side Ethernet interfaces, but not to those
   on the WAN side.  Finally, a third set of rules could be associated
   with the role-combination "Ethernet"+"WAN"; these rules would apply to
   the WAN-side Ethernet interfaces, but not to those on the campus side.
   (The roles in a role-combination appear in alphabetical order in these
   examples, because that is how they appear in the information model.)
 
   If we have a specific interface A that's associated with the role-
   combination "Ethernet"+"WAN", we see that it should have three
   categories of policy rules applied to it:  those for the "Ethernet"
   role, those for the "WAN" role, and those for the role-combination
   "Ethernet"+"WAN".  Going one step further, if interface B is
   associated with the role-combination "branch-office"+"Ethernet"+"WAN",
   then B should have seven categories of policy rules applied to it -
   those associated with the following role-combinations:
 
     o  "branch-office"
     o  "Ethernet"
     o  "WAN"
     o  "branch-office"+"Ethernet"
     o  "branch-office"+"WAN"
     o  "Ethernet"+"WAN"
     o  "branch-office"+"Ethernet"+"WAN".
 
   In order to get all of the right policy rules for a resource like
   interface B, a PDP must expand the single role-combination it receives
   for B into this list of seven role-combinations, and then retrieve
   from the Policy Repository the corresponding seven sets of policy
   rules.  Of course this example is unusually complicated:  the normal
   case will involve expanding a two-role combination into three values
   identifying three sets of policy rules.
 
   Role-combinations also help to simplify somewhat the problem of
   identifying conflicts between policy rules.  With role-combinations,
   it is possible for a policy administrator to specify one set of policy
   rules for campus-side Ethernet interfaces, and a second set of policy
   rules for WAN-side Ethernet interfaces, without having to worry about
   conflicts between the two sets of rules.  The policy administrator
   simply "turns off" conflict detection for these two sets of rules, by
   telling the policy management system that the roles "Campus" and "WAN"
   are incompatible with each other.  This indicates that the role
   combination will never occur, and therefore conflicts will never
   occur.  In some cases the technology itself might identify
 
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   incompatible roles:  "Ethernet" and "FrameRelay", for example.  But
   for less precise terms like "Campus" and "WAN", the policy
   administrator must say whether they identify incompatible roles.
 
   When the policy administrator does this, there are three effects:
 
   1. If an interface has assigned to it a role-combination involving
      both "Campus" and "WAN", then the policy management system can flag
      it as an error.
 
   2. If a policy rule is associated with a role-combination involving
      both "Campus" and "WAN", then the policy management system can flag
      it as an error.
 
   3. If the policy management system sees two policy rules, where one is
      tied to the role "Campus" (or to a role-combination that includes
      the role "Campus") and the other is tied to the role "WAN" (or to a
      role-combination that includes the role "WAN"), then the system
      does not need to look for conflicts between the two policy rules:
      because of the incompatible roles, the two rules cannot possibly
      conflict.
 
 
 
                        +-------------------+
                        | Policy Repository |
                        +-------------------+
                                  V
                                  V retrieval of policy
                                  V
                             +---------+
                             | PDP/PEP |
                             +---------+
                                  v
                                  v application of policy
                                  v
                          +----------------+
                          | Network Entity |
                          +----------------+
 
   Figure 4.    Retrieval and Application of a Policy
 
   Figure 4, which is introduced only as an example of how the Policy
   Framework might be implemented by a collection of network components,
   illustrates how roles operate within the Policy Framework.  Because
   the distinction between them is not important to this discussion, the
   PDP and the PEP are combined in one box.  The points illustrated here
   apply equally well, though, to an environment where the PDP and the
   PEP are implemented separately.
 
   A role represents a functional characteristic or capability of a
   resource to which policies are applied.  Examples of roles include
   Backbone interface, Frame Relay interface, BGP-capable router, web
 
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   server, firewall, etc.  The multiple roles assigned to a single
   resource are combined to form that resource's role combination.  Role
   combinations are represented in the PCIM by values of the PolicyRoles
   property in the PolicyRule class.  A PDP uses policy roles as follows
   to identify the policies it needs to be aware of:
 
   1.  The PDP learns in some way the list of roles that its PEPs play.
       This information might be configured at the PDP, the PEPs might
       supply it to the PDP, or the PDP might retrieve it from a
       repository.
 
   2.  Using repository-specific means, the PDP determines where to look
       for policy rules that might apply to it.
 
   3.  Using the roles and role-combinations it received from its PEPs
       as indicated in the examples above, the PDP is able to locate and
       retrieve the policy rules that are relevant to it.
 
 5.2.2. The PolicyRoles Property
 
   As indicated earlier, PolicyRoles is a property associated with a
   policy rule. It is an array holding "role combinations" for the policy
   rule, and correlates with the roles defined for a network resource.
   Using the PolicyRoles property, it is possible to mark a policy rule
   as applying, for example, to a Frame Relay interface or to a backbone
   ATM interface.  The PolicyRoles property take strings of the form:
 
      <RoleName>[&&<RoleName>]*
 
   Each value of this property represents a role combination, including
   the special case of a "combination" containing only one role.  As the
   format indicates, the role names in a role combination are ANDed
   together to form a single selector.  The multiple values of the
   PolicyRoles property are logically ORed, to make it possible for a
   policy rule to have multiple selectors.
 
   The individual role names in a role combination must appear in
   alphabetical order (according to the collating sequence for UCS-2
   characters), to make the string matches work correctly.  The role
   names used in an environment are specified by the policy
   administrator.
 
 5.3. Local Time and UTC Time in PolicyTimePeriodConditions
 
   An instance of PolicyTimePeriodCondition has up to five properties
   that represent times:  TimePeriod, MonthOfYearMask, DayOfMonthMask,
   DayOfWeekMask, and TimeOfDayMask.  All of the time-related properties
   in an instance of PolicyTimePeriodCondition represent one of two types
   of times:  local time at the place where a policy rule is applied, or
   UTC time.  The property LocalOrUtcTime indicates which time
   representation applies to an instance of PolicyTimePeriodCondition.
 
 
 
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   Since the PCIM provides only for local time and UTC time, a Policy
   Management Tool that provides for other time representations (for
   example, a fixed time at a particular location) will need to map from
   these other representations to either local time or UTC time.  An
   example will illustrate the nature of this mapping.
 
   Suppose a policy rule is tied to the hours of operation for a Help
   Desk:  0800 to 2000 Monday through Friday [US] Eastern Time.  In order
   to express these times in PolicyTimePeriodCondition, a management tool
   must convert them to UTC times.  (They are not local times, because
   they refer to a single time interval worldwide, not to intervals tied
   to the local clocks at the locations where the PolicyRule is being
   applied.)  As reference [10] points out, mapping from [US] Eastern
   Time to UTC time is not simply a matter of applying an offset:  the
   offset between [US] Eastern Time and UTC time switches between -0500
   and -0400 depending on whether Daylight Savings Time is in effect in
   the US.
 
   Suppose the policy administrator's goal is to have a policy rule be
   valid from 0800 until 1200 [US] Eastern Time on every Monday, within
   the overall time period from the beginning of 2000 until the end of
   2001.  The Policy Management Tool could either be configured with the
   definition of what [US] Eastern Time means, or it could be configured
   with knowledge of where to go to get this information.  Reference [10]
   contains further discussion of time zone definitions and where they
   might reside.
 
   Armed with knowledge about [US] Eastern Time, the Policy Management
   Tool would create however many instances of PolicyTimePeriodCondition
   it needed to represent the desired intervals.  Note that while there
   is an increased number of PolicyTimePeriodCondition instances, there
   is still just one PolicyRule, which is tied to all the
   PolicyTimePeriodCondition instances via the aggregation
   PolicyRuleValidityPeriod.  Here are the first two of these instances:
 
         1. TimePeriod:  20000101T050000/20000402T070000
            DayOfWeekMask:  { Monday }
            TimeOfDayMask:  T130000/T170000
            LocalOrUtcTime:  UTC
 
         2. TimePeriod:  20000402T070000/20001029T070000
            DayOfWeekMask:  { Monday }
            TimeOfDayMask:  T120000/T160000
            LocalOrUtcTime:  UTC
 
 
   There would be three more similar instances, for winter 2000-2001,
   summer 2001, and winter 2001 up through December 31.
 
   Had the example been chosen differently, there could have been even
   more instances of PolicyTimePeriodCondition.  If, for example, the
 
 
 
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   time interval had been from 0800 - 2200 [US] Eastern Time on Mondays,
   instance 1 above would have split into two instances:  one with a UTC
   time interval of T130000/T240000 on Mondays, and another with a UTC
   time interval of T000000/T030000 on Tuesdays.  So the end result would
   have been ten instances of PolicyTimePeriodCondition, not five.
 
   By restricting PolicyTimePeriodCondition to local time and UTC time,
   the PCIM places the difficult and expensive task of mapping from
   "human" time representations to machine-friendly ones in the Policy
   Management Tool.  Another approach would have been to place in
   PolicyTimePeriodCondition a means of representing a named time zone,
   such as [US] Eastern Time.  This, however, would have passed the
   difficult mapping responsibility down to the PDPs and PEPs.  It is
   better to have a mapping such as the one described above done once in
   a Policy Management Tool, rather than having it done over and over in
   each of the PDPs (and possibly PEPs) that need to apply a PolicyRule.
 
 5.4. CIM Data Types
 
   Since PCIM extends the CIM Schema, a correspondence between data types
   used in both CIM and PCIM is needed. The following CIM data types are
   used in the class definitions that follow in Sections 6 and 7:
 
   o uint8               unsigned 8-bit integer
 
   o uint16              unsigned 16-bit integer
 
   o boolean             Boolean
 
   o string              UCS-2 string.
 
   Strings in CIM are stored as UCS-2 characters, where each character is
   encoded in two octets.  Thus string values may need to be converted
   when moving between a CIM environment and one that uses a different
   string encoding.  For example, in an LDAP-accessible directory,
   attributes of type DirectoryString are stored in UTF-8 format.  RFC
   2279 [7] explains how to convert between these two formats.
 
   When it is applied to a CIM string, a MaxLen value refers to the
   maximum number of characters in the string, rather than to the maximum
   number of octets.
 
   In addition to the CIM data types listed above, the association
   classes in Section 7 use the following type:
 
   o <classname> ref     strongly typed reference.
 
 
 6. Class Definitions
 
   There are a significant number of differences between CIM and LDAP
   class specifications.  The ones that are relevant to the abbreviated
   class specifications in this document are the following:
 
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   o Instead of LDAP's three class types (abstract, auxiliary,
     structural), CIM has only two:  abstract and instantiable.  The
     type of a CIM class is indicated by the Boolean qualifier ABSTRACT.
 
   o CIM uses the term "property" for what LDAP terms an "attribute".
 
   o CIM uses the array notation "[ ]" to indicate that a property is
     multi-valued.  CIM defines three types of arrays: bags (contents
     are unordered, duplicates allowed), ordered bags (contents are
     ordered but duplicates are allowed) and indexed arrays (contents
     are ordered and no duplicates are allowed).
 
   o CIM classes and properties are identified by name, not by OID.
 
   o CIM classes use a different naming scheme for native
     implementations, than LDAP.  The CIM naming scheme is documented in
     Appendix A since it is not critical to understanding the
     information model, and only applies when communicating with a
     native CIM implementation.
 
   o In LDAP, attribute definitions are global, and the same attribute
     may appear in multiple classes.  In CIM, a property is defined
     within the scope of a single class definition.  The property may be
     inherited into subclasses of the class in which it is defined, but
     otherwise it cannot appear in other classes.  One side effect of
     this difference is that CIM property names tend to be much shorter
     than LDAP attribute names, since they are implicitly scoped by the
     name of the class in which they are defined.
 
   There is also a notational convention that this document follows, to
   improve readability.  In CIM, all class and property names are
   prefixed with the characters "CIM_".  These prefixes have been omitted
   throughout this document, with one exception regarding naming,
   documented in Appendix A.
 
   For the complete definition of the CIM specification language, see
   reference [2].
 
 6.1. The Abstract Class "Policy"
 
   The abstract class Policy collects several properties that may be
   included in instances of any of the Core Policy classes (or their
   subclasses).  For convenience, the two properties that Policy inherits
   from ManagedElement in the CIM schema are shown here as well.
 
   The class definition is as follows:
 
     NAME             Policy
     DESCRIPTION      An abstract class with four properties for
                      describing a policy-related instance.
     DERIVED FROM     ManagedElement
     ABSTRACT         TRUE
     PROPERTIES       CommonName (CN)
 
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                      PolicyKeywords[ ]
                             // Caption (inherited)
                             // Description (inherited)
 
 6.1.1. The Property "CommonName (CN)"
 
   The CN, or CommonName, property corresponds to the X.500 attribute
   commonName (cn).  In X.500 this property specifies one or more user-
   friendly names (typically only one name) by which an object is
   commonly known, names that conform to the naming conventions of the
   country or culture with which the object is associated.  In the CIM
   model, however, the CommonName property is single-valued.
 
     NAME             CN
     DESCRIPTION      A user-friendly name of a policy-related object.
     SYNTAX           string
 
 6.1.2. The Multi-valued Property "PolicyKeywords"
 
   This property provides a set of one or more keywords that a policy
   administrator may use to assist in characterizing or categorizing a
   policy object.  Keywords are of one of two types:
 
   o Keywords defined in this document, or in documents that define
     subclasses of the classes defined in this document.  These keywords
     provide a vendor-independent, installation-independent way of
     characterizing policy objects.
 
   o Installation-dependent keywords for characterizing policy objects.
     Examples include "Engineering", "Billing", and "Review in December
     2000".
 
   This document defines the following keywords:  "UNKNOWN",
   "CONFIGURATION", "USAGE", "SECURITY", "SERVICE", "MOTIVATIONAL",
   "INSTALLATION", and "EVENT".  These concepts were defined earlier in
   Section 2.
 
   One additional keyword is defined:  "POLICY".  The role of this
   keyword is to identify policy-related instances that would not
   otherwise be identifiable as being related to policy.  It may be
   needed in some repository implementations.
 
   Documents that define subclasses of the Policy Core Information Model
   classes SHOULD define additional keywords to characterize instances of
   these subclasses.  By convention, keywords defined in conjunction with
   class definitions are in uppercase.  Installation-defined keywords can
   be in any case.
 
   The property definition is as follows:
 
     NAME             PolicyKeywords
     DESCRIPTION      A set of keywords for characterizing /categorizing
                      policy objects.
 
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     SYNTAX           string
 
 6.1.3. The Property "Caption" (Inherited from ManagedElement)
 
   This property provides a one-line description of a policy-related
   object.
 
     NAME             Caption
     DESCRIPTION      A one-line description of this policy-related
                      object.
     SYNTAX           string
 
 6.1.4. The Property "Description" (Inherited from ManagedElement)
 
   This property provides a longer description than that provided by the
   caption property.
 
     NAME             Description
     DESCRIPTION      A long description of this policy-related object.
     SYNTAX           string
 
 6.2. The Class "PolicyGroup"
 
   This class is a generalized aggregation container.  It enables either
   PolicyRules or PolicyGroups, but not both, to be aggregated in a
   single container.  Loops, including the degenerate case of a
   PolicyGroup that contains itself, are not allowed when PolicyGroups
   contain other PolicyGroups.
 
   PolicyGroups and their nesting capabilities are shown in Figure 5
   below. Note that a PolicyGroup can nest other PolicyGroups, and there
   is no restriction on the depth of the nesting in sibling PolicyGroups.
 
     +---------------------------------------------------+
     |                    PolicyGroup                    |
     |                                                   |
     | +--------------------+       +-----------------+  |
     | |    PolicyGroup A   |       |  PolicyGroup X  |  |
     | |                    |       |                 |  |
     | | +----------------+ |  ooo  |                 |  |
     | | | PolicyGroup A1 | |       |                 |  |
     | | +----------------+ |       |                 |  |
     | +--------------------+       +-----------------+  |
     +---------------------------------------------------+
 
   Figure 5.    Overview of the PolicyGroup class
 
   As a simple example, think of the highest level PolicyGroup shown in
   Figure 5 above as a logon policy for US employees of a company. This
   PolicyGroup may be called USEmployeeLogonPolicy, and may aggregate
   several PolicyGroups that provide specialized rules per location.
   Hence, PolicyGroup A in Figure 5 above may define logon rules for
 
 
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   employees on the West Coast, while another PolicyGroup might define
   logon rules for the Midwest (e.g., PolicyGroup X), and so forth.
 
   Note also that the depth of each PolicyGroup does not need to be the
   same. Thus, the WestCoast PolicyGroup might have several additional
   layers of PolicyGroups defined for any of several reasons (different
   locales, number of subnets, etc.). The PolicyRules are therefore
   contained at n levels from the USEmployeeLogonPolicyGroup. Compare
   this to the Midwest PolicyGroup (PolicyGroup X), which might directly
   contain PolicyRules.
 
   The class definition for PolicyGroup is as follows:
 
     NAME             PolicyGroup
     DESCRIPTION      A container for either a set of related PolicyRules
                      or a set of related PolicyGroups.
     DERIVED FROM     Policy
     ABSTRACT         FALSE
     PROPERTIES       NONE
 
  No properties are defined for this class since it inherits all its
  properties from Policy.  The class exists to aggregate PolicyRules or
  other PolicyGroups.  It is directly instantiable.  In an
  implementation, various key/identification properties MUST be defined.
  The keys for a native CIM implementation are defined in Appendix A,
  Section 14.1.1.  Keys for an LDAP implementation are defined in the
  LDAP mapping of this information model [11].
 
 6.3. The Class "PolicyRule"
 
   This class represents the "If Condition then Action" semantics
   associated with a policy.  A PolicyRule condition, in the most general
   sense, is represented as either an ORed set of ANDed conditions
   (Disjunctive Normal Form, or DNF) or an ANDed set of ORed conditions
   (Conjunctive Normal Form, or CNF). Individual conditions may either be
   negated (NOT C) or unnegated (C).  The actions specified by a
   PolicyRule are to be performed if and only if the PolicyRule condition
   (whether it is represented in DNF or CNF) evaluates to TRUE.
 
   The conditions and actions associated with a policy rule are modeled,
   respectively, with subclasses of the classes PolicyCondition and
   PolicyAction.  These condition and action objects are tied to
   instances of PolicyRule by the PolicyConditionInPolicyRule and
   PolicyActionInPolicyRule aggregations.
 
   As illustrated above in Section 3, a policy rule may also be
   associated with one or more policy time periods, indicating the
   schedule according to which the policy rule is active and inactive.
   In this case it is the PolicyRuleValidityPeriod aggregation that
   provides the linkage.
 
   A policy rule is illustrated conceptually in Figure 6. below.
 
 
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     +------------------------------------------------+
     |                    PolicyRule                  |
     |                                                |
     | +--------------------+     +-----------------+ |
     | | PolicyCondition(s) |     | PolicyAction(s) | |
     | +--------------------+     +-----------------+ |
     |                                                |
     |        +------------------------------+        |
     |        | PolicyTimePeriodCondition(s) |        |
     |        +------------------------------+        |
     +------------------------------------------------+
 
   Figure 6.    Overview of the PolicyRule Class
 
   The PolicyRule class uses the property ConditionListType, to indicate
   whether the conditions for the rule are in DNF or CNF.  The
   PolicyConditionInPolicyRule aggregation contains two additional
   properties to complete the representation of the rule's conditional
   expression.  The first of these properties is an integer to partition
   the referenced conditions into one or more groups, and the second is a
   Boolean to indicate whether a referenced condition is negated.  An
   example shows how ConditionListType and these two additional
   properties provide a unique representation of a set of conditions in
   either DNF or CNF.
 
   Suppose we have a PolicyRule that aggregates five PolicyConditions C1
   through C5, with the following values in the properties of the five
   PolicyConditionInPolicyRule associations:
 
    C1:  GroupNumber = 1, ConditionNegated = FALSE
    C2:  GroupNumber = 1, ConditionNegated = TRUE
    C3:  GroupNumber = 1, ConditionNegated = FALSE
    C4:  GroupNumber = 2, ConditionNegated = FALSE
    C5:  GroupNumber = 2, ConditionNegated = FALSE
 
 
   If ConditionListType = DNF, then the overall condition for the
   PolicyRule is:
 
        (C1 AND (NOT C2) AND C3) OR (C4 AND C5)
 
   On the other hand, if ConditionListType = CNF, then the overall
   condition for the PolicyRule is:
 
        (C1 OR (NOT C2) OR C3) AND (C4 OR C5)
 
   In both cases, there is an unambiguous specification of the overall
   condition that is tested to determine whether to perform the actions
   associated with the PolicyRule.
 
   The class definition is as follows:
 
     NAME             PolicyRule
 
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     DESCRIPTION      The central class for representing the "If
                      Condition then Action" semantics associated with a
                      policy rule.
     DERIVED FROM     Policy
     ABSTRACT         FALSE
     PROPERTIES       Enabled
                      ConditionListType
                      RuleUsage
                      Priority
                      Mandatory
                      SequencedActions
                      PolicyRoles
 
   The PolicyRule class is directly instantiable. In an implementation,
   various key/identification properties MUST be defined.  The keys for a
   native CIM implementation are defined in Appendix A, Section 14.1.2.
   Keys for an LDAP implementation are defined in the LDAP mapping of
   this information model [11].
 
 6.3.1. The Property "Enabled"
 
   This property indicates whether a policy rule is currently enabled,
   from an administrative point of view.  Its purpose is to allow a
   policy administrator to enable or disable a policy rule without having
   to add it to, or remove it from, the policy repository.
 
   The property also supports the value 'enabledForDebug'.  When the
   property has this value, the entity evaluating the policy condition(s)
   is being told to evaluate the conditions for the policy rule, but not
   to perform the actions if the conditions evaluate to TRUE.  This value
   serves as a debug vehicle when attempting to determine what policies
   would execute in a particular scenario, without taking any actions to
   change state during the debugging.
 
   The property definition is as follows:
 
     NAME             Enabled
     DESCRIPTION      An enumeration indicating whether a policy rule is
                      administratively enabled, administratively
                      disabled, or enabled for debug mode.
     SYNTAX           uint16
     VALUES           enabled(1), disabled(2), enabledForDebug(3)
     DEFAULT VALUE    enabled(1)
 
 6.3.2. The Property "ConditionListType"
 
   This property is used to specify whether the list of policy conditions
   associated with this policy rule is in disjunctive normal form (DNF)
   or conjunctive normal form (CNF).  If this property is not present,
   the list type defaults to DNF.  The property definition is as follows:
 
     NAME             ConditionListType
 
 
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     DESCRIPTION      Indicates whether the list of policy conditions
                      associated with this policy rule is in disjunctive
                      normal form (DNF) or conjunctive normal form (CNF).
     SYNTAX           uint16
     VALUES           DNF(1), CNF(2)
     DEFAULT VALUE    DNF(1)
 
 6.3.3. The Property "RuleUsage"
 
   This property is a free-form string that recommends how this policy
   should be used. The property definition is as follows:
 
     NAME             RuleUsage
     DESCRIPTION      This property is used to provide guidelines on how
                      this policy should be used.
     SYNTAX           string
 
 6.3.4. The Property "Priority"
 
   This property provides a non-negative integer for prioritizing policy
   rules relative to each other.  For policy rules that have this
   property, larger integer values indicate higher priority.  Since one
   purpose of this property is to allow specific, ad hoc policy rules to
   temporarily override established policy rules, an instance that has
   this property set has a higher priority than all instances that lack
   it.
 
   Prioritization among policy rules provides a basic mechanism for
   resolving policy conflicts.
 
   The property definition is as follows:
 
     NAME             Priority
     DESCRIPTION      A non-negative integer for prioritizing this
                      PolicyRule relative to other PolicyRules.  A larger
                      value indicates a higher priority.
     SYNTAX           uint16
     DEFAULT VALUE    0
 
 6.3.5. The Property "Mandatory"
 
   This property indicates whether evaluation (and possibly action
   execution) of a PolicyRule is mandatory or not.  Its concept is
   similar to the ability to mark packets for delivery or possible
   discard, based on network traffic and device load.
 
   The evaluation of a PolicyRule MUST be attempted if the Mandatory
   property value is TRUE.  If the Mandatory property value of a
   PolicyRule is FALSE, then the evaluation of the rule is "best effort"
   and MAY be ignored.
 
   The property definition is as follows:
 
 
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     NAME             Mandatory
     DESCRIPTION      A flag indicating that the evaluation of the
                      PolicyConditions and execution of PolicyActions (if
                      the condition list evaluates to TRUE) is required.
     SYNTAX           boolean
     DEFAULT VALUE    TRUE
 
 6.3.6. The Property "SequencedActions"
 
   This property gives a policy administrator a way of specifying how the
   ordering of the policy actions associated with this PolicyRule is to
   be interpreted.  Three values are supported:
 
   o mandatory(1):   Do the actions in the indicated order, or don't do
     them at all.
 
   o recommended(2): Do the actions in the indicated order if you can,
     but if you can't do them in this order, do them in another order if
     you can.
 
   o dontCare(3):    Do them -- I don't care about the order.
 
   When error / event reporting is addressed for the Policy Framework,
   suitable codes will be defined for reporting that a set of actions
   could not be performed in an order specified as mandatory (and thus
   were not performed at all), that a set of actions could not be
   performed in a recommended order (and moreover could not be performed
   in any order), or that a set of actions could not be performed in a
   recommended order (but were performed in a different order). The
   property definition is as follows:
 
     NAME             SequencedActions
     DESCRIPTION      An enumeration indicating how to interpret the
                      action ordering indicated via the
                      PolicyActionInPolicyRule aggregation.
     SYNTAX           uint16
     VALUES           mandatory(1), recommended(2), dontCare(3)
     DEFAULT VALUE    dontCare(3)
 
 6.3.7. The Multi-valued Property "PolicyRoles"
 
   This property represents the roles and role combinations associated
   with a policy rule.  Each value represents one role combination.
   Since this is a multi-valued property, more than one role combination
   can be associated with a single policy rule.  Each value is a string
   of the form
 
      <RoleName>[&&<RoleName>]*
 
   where the individual role names appear in alphabetical order
   (according to the collating sequence for UCS-2).  The property
   definition is as follows:
 
 
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     NAME             PolicyRoles
     DESCRIPTION      A set of strings representing the roles and role
                      combinations associated with a policy rule.  Each
                      value represents one role combination.
     SYNTAX           string
 
 6.4. The Class "PolicyCondition"
 
   The purpose of a policy condition is to determine whether or not the
   set of actions (aggregated in the PolicyRule that the condition
   applies to) should be executed or not. For the purposes of the Policy
   Core Information Model, all that matters about an individual
   PolicyCondition is that it evaluates to TRUE or FALSE.  (The
   individual PolicyConditions associated with a PolicyRule are combined
   to form a compound expression in either DNF or CNF, but this is
   accomplished via the ConditionListType property, discussed above, and
   by the properties of the PolicyConditionInPolicyRule aggregation,
   introduced above and discussed further in Section 7.6 below.)  A
   logical structure within an individual PolicyCondition may also be
   introduced, but this would have to be done in a subclass of
   PolicyCondition.
 
   Because it is general, the PolicyCondition class does not itself
   contain any "real" conditions.  These will be represented by
   properties of the domain-specific subclasses of PolicyCondition.
 
   +---------------------------------------------------------------+
   |                    Policy Conditions in DNF                   |
   | +-------------------------+         +-----------------------+ |
   | |       AND list          |         |      AND list         | |
   | |  +-------------------+  |         |  +-----------------+  | |
   | |  |  PolicyCondition  |  |         |  | PolicyCondition |  | |
   | |  +-------------------+  |         |  +-----------------+  | |
   | |  +-------------------+  |         |  +-----------------+  | |
   | |  |  PolicyCondition  |  |   ...   |  | PolicyCondition |  | |
   | |  +-------------------+  |   ORed  |  +-----------------+  | |
   | |          ...            |         |         ...           | |
   | |         ANDed           |         |        ANDed          | |
   | |  +-------------------+  |         |  +-----------------+  | |
   | |  |  PolicyCondition  |  |         |  | PolicyCondition |  | |
   | |  +-------------------+  |         |  +-----------------+  | |
   | +-------------------------+         +-----------------------+ |
   +---------------------------------------------------------------+
 
 
   Figure 7.    Overview of Policy Conditions in DNF
 
   This figure illustrates that when policy conditions are in DNF, there
   are one or more sets of conditions that are ANDed together to form AND
   lists.  An AND list evaluates to TRUE if and only if all of its
   constituent conditions evaluate to TRUE.  The overall condition then
   evaluates to TRUE if and only if at least one of its constituent AND
   lists evaluates to TRUE.
 
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   +---------------------------------------------------------------+
   |                    Policy Conditions in CNF                   |
   | +-------------------------+         +-----------------------+ |
   | |        OR list          |         |       OR list         | |
   | |  +-------------------+  |         |  +-----------------+  | |
   | |  |  PolicyCondition  |  |         |  | PolicyCondition |  | |
   | |  +-------------------+  |         |  +-----------------+  | |
   | |  +-------------------+  |         |  +-----------------+  | |
   | |  |  PolicyCondition  |  |   ...   |  | PolicyCondition |  | |
   | |  +-------------------+  |  ANDed  |  +-----------------+  | |
   | |          ...            |         |         ...           | |
   | |         ORed            |         |         ORed          | |
   | |  +-------------------+  |         |  +-----------------+  | |
   | |  |  PolicyCondition  |  |         |  | PolicyCondition |  | |
   | |  +-------------------+  |         |  +-----------------+  | |
   | +-------------------------+         +-----------------------+ |
   +---------------------------------------------------------------+
 
 
   Figure 8.    Overview of Policy Conditions in CNF
 
   In this figure, the policy conditions are in CNF.  Consequently, there
   are one or more OR lists, each of which evaluates to TRUE if and only
   if at least one of its constituent conditions evaluates to TRUE.  The
   overall condition then evaluates to TRUE if and only if ALL of its
   constituent OR lists evaluate to TRUE.
 
   The class definition of PolicyCondition is as follows:
 
     NAME             PolicyCondition
     DESCRIPTION      A class representing a rule-specific or reusable
                      policy condition to be evaluated in conjunction
                      with a policy rule.
     DERIVED FROM     Policy
     ABSTRACT         FALSE
     PROPERTIES       NONE
 
   No properties are defined for this class since it inherits all its
   properties from Policy.  The class exists as an abstract superclass
   for domain-specific policy conditions, defined in subclasses.  In an
   implementation, various key/identification properties MUST be defined
   for the class or its instantiable subclasses.  The keys for a native
   CIM implementation are defined in Appendix A, Section 14.2.  Keys for
   an LDAP implementation are defined in the LDAP mapping of this
   information model [11].
 
   When identifying and using the PolicyCondition class, it is necessary
   to remember that a condition can be rule-specific or reusable.  This
   was discussed above in Section 5.1. The distinction between the two
   types of policy conditions lies in the associations in which an
   instance can participate, and in how the different instances are
   named.  Conceptually, a reusable policy condition resides in a policy
   repository, and is named within the scope of that repository.  On the
 
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   other hand, a rule-specific policy condition is, as the name suggests,
   named within the scope of the single policy rule to which it is
   related.
 
   The distinction between rule-specific and reusable PolicyConditions
   affects the CIM naming, defined in Appendix A, and the LDAP mapping
   [11].
 
 
 6.5. The Class "PolicyTimePeriodCondition"
 
   This class provides a means of representing the time periods during
   which a policy rule is valid, i.e., active.  At all times that fall
   outside these time periods, the policy rule has no effect.  A policy
   rule is treated as valid at all times if it does not specify a
   PolicyTimePeriodCondition.
 
   In some cases a PDP may need to perform certain setup / cleanup
   actions when a policy rule becomes active / inactive.  For example,
   sessions that were established while a policy rule was active might
   need to be taken down when the rule becomes inactive.  In other cases,
   however, such sessions might be left up:  in this case, the effect of
   deactivating the policy rule would just be to prevent the
   establishment of new sessions.  Setup / cleanup behaviors on validity
   period transitions are not currently addressed by the PCIM, and must
   be specified in 'guideline' documents, or via subclasses of
   PolicyRule, PolicyTimePeriodCondition or other concrete subclasses of
   Policy.  If such behaviors need to be under the control of the policy
   administrator, then a mechanism to allow this control must also be
   specified in the subclass.
 
   PolicyTimePeriodCondition is defined as a subclass of PolicyCondition.
   This is to allow the inclusion of time-based criteria in the AND/OR
   condition definitions for a PolicyRule.
 
   Instances of this class may have up to five properties identifying
   time periods at different levels.  The values of all the properties
   present in an instance are ANDed together to determine the validity
   period(s) for the instance.  For example, an instance with an overall
   validity range of January 1, 2000 through December 31, 2000; a month
   mask that selects March and April; a day-of-the-week mask that selects
   Fridays; and a time of day range of 0800 through 1600 would represent
   the following time periods:
 
 
 
 
 
 
 
 
 
 
 
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       Friday, March  5, 2000, from 0800 through 1600;
       Friday, March 12, 2000, from 0800 through 1600;
       Friday, March 19, 2000, from 0800 through 1600;
       Friday, March 26, 2000, from 0800 through 1600;
       Friday, April  2, 2000, from 0800 through 1600;
       Friday, April  9, 2000, from 0800 through 1600;
       Friday, April 16, 2000, from 0800 through 1600;
       Friday, April 23, 2000, from 0800 through 1600;
       Friday, April 30, 2000, from 0800 through 1600.
 
 
   Properties not present in an instance of PolicyTimePeriodCondition are
   implicitly treated as having their value "always enabled". Thus, in
   the example above, the day-of-the-month mask is not present, and so
   the validity period for the instance implicitly includes a day-of-the-
   month mask that selects all days of the month.  If we apply this
   "missing property" rule to its fullest, we see that there is a second
   way to indicate that a policy rule is always enabled: have it point to
   an instance of PolicyTimePeriodCondition whose only properties are its
   naming properties.
 
   The property LocalOrUtcTime indicates whether the times represented in
   the other five time-related properties of an instance of
   PolicyTimePeriodCondition are to be interpreted as local times for the
   location where a policy rule is being applied, or as UTC times.
 
   The class definition is as follows.
 
     NAME             PolicyTimePeriodCondition
     DESCRIPTION      A class that provides the capability of enabling /
                      disabling a policy rule according to a pre-
                      determined schedule.
     DERIVED FROM     PolicyCondition
     ABSTRACT         FALSE
     PROPERTIES       TimePeriod
                      MonthOfYearMask
                      DayOfMonthMask
                      DayOfWeekMask
                      TimeOfDayMask
                      LocalOrUtcTime
 
 6.5.1. The Property "TimePeriod"
 
   This property identifies an overall range of calendar dates and times
   over which a policy rule is valid.  It reuses the format for an
   explicit time period defined in RFC 2445 (reference [10]): a string
   representing a starting date and time, in which the character 'T'
   indicates the beginning of the time portion, followed by the solidus
   character '/', followed by a similar string representing an end date
   and time.  The first date indicates the beginning of the range, while
   the second date indicates the end.  Thus, the second date and time
   must be later than the first.  Date/times are expressed as substrings
   of the form "yyyymmddThhmmss".  For example:
 
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     20000101T080000/20000131T120000
 
         January 1, 2000, 0800 through January 31, 2000, noon
 
   There are also two special cases in which one of the date/time strings
   is replaced with a special string defined in RFC 2445.
 
   o If the first date/time is replaced with the string "THISANDPRIOR",
     then the property indicates that a policy rule is valid [from now]
     until the date/time that appears after the '/'.
 
   o If the second date/time is replaced with the string
     "THISANDFUTURE", then the property indicates that a policy rule
     becomes valid on the date/time that appears before the '/', and
     remains valid from that point on.
 
   Note that RFC 2445 does not use these two strings in connection with
   explicit time periods.  Thus the PCIM is combining two elements from
   RFC 2445 that are not combined in the RFC itself.
 
   The property definition is as follows:
 
     NAME             TimePeriod
     DESCRIPTION      The range of calendar dates on which a policy rule
                      is valid.
     SYNTAX           string
     FORMAT           yyyymmddThhmmss/yyyymmddThhmmss, where the first
                      date/time may be replaced with the string
                      "THISANDPRIOR" or the second date/time may be
                      replaced with the string "THISANDFUTURE"
 
 6.5.2. The Property "MonthOfYearMask"
 
   The purpose of this property is to refine the definition of the valid
   time period that is defined by the TimePeriod property, by explicitly
   specifying which months the policy is valid for.  These properties
   work together, with the TimePeriod used to specify the overall time
   period that the policy is valid for, and the MonthOfYearMask used to
   pick out which months of that time period the policy is valid for.
 
   This property is formatted as an octet string, structured as follows:
 
   o a 4-octet length field, indicating the length of the entire octet
     string; this field is always set to 0x00000006 for this property;
 
   o a 2-octet field consisting of 12 bits identifying the 12 months of
     the year, beginning with January and ending with December, followed
     by 4 bits that are always set to '0'.  For each month, the value
     '1' indicates that the policy is valid for that month, and the
     value '0' indicates that it is not valid.
 
   The value 0x000000060830, for example, indicates that a policy rule is
   valid only in the months May, November, and December .
 
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   If this property is omitted, then the policy rule is treated as valid
   for all twelve months.  The property definition is as follows:
 
     NAME             MonthOfYearMask
     DESCRIPTION      A mask identifying the months of the year in which
                      a policy rule is valid.
     SYNTAX           octet string
     FORMAT           0x00000006XXX0
 
 6.5.3. The Property "DayOfMonthMask"
 
   The purpose of this property is to refine the definition of the valid
   time period that is defined by the TimePeriod property, by explicitly
   specifying which days of the month the policy is valid for.  These
   properties work together, with the TimePeriod used to specify the
   overall time period that the policy is valid for, and the
   DayOfMonthMask used to pick out which days of the month in that time
   period the policy is valid for.
 
   This property is formatted as an octet string, structured as follows:
 
   o a 4-octet length field, indicating the length of the entire octet
     string; this field is always set to 0x0000000C for this property;
 
   o an 8-octet field consisting of 31 bits identifying the days of the
     month counting from the beginning, followed by 31 more bits
     identifying the days of the month counting from the end, followed
     by 2 bits that are always set to '0'.  For each day, the value '1'
     indicates that the policy is valid for that day, and the value '0'
     indicates that it is not valid.
 
   The value 0x0000000C8000000100000000, for example, indicates that a
   policy rule is valid on the first and last days of the month.
 
   For months with fewer than 31 days, the digits corresponding to days
   that the months do not have (counting in both directions) are ignored.
 
   The encoding of the 62 significant bits in the octet string matches
   that used for the schedDay object in the DISMAN-SCHEDULE-MIB.  See
   reference [8] for more details on this object.
 
   The property definition is as follows:
 
     NAME             DayOfMonthMask
     DESCRIPTION      A mask identifying the days of the month on which a
                      policy rule is valid.
     SYNTAX           octet string
     FORMAT           0x0000000CXXXXXXXXXXXXXXXX
 
 
 
 
 
 
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 6.5.4. The Property "DayOfWeekMask"
 
   The purpose of this property is to refine the definition of the valid
   time period that is defined by the TimePeriod property by explicitly
   specifying which days of the week the policy is valid for. These
   properties work together, with the TimePeriod used to specify the
   overall time period that the policy is valid for, and the
   DayOfWeekMask used to pick out which days of the week in that time
   period the policy is valid for.
 
   This property is formatted as an octet string, structured as follows:
 
   o a 4-octet length field, indicating the length of the entire octet
     string; this field is always set to 0x00000005 for this property;
 
   o a 1-octet field consisting of 7 bits identifying the 7 days of the
     week, beginning with Sunday and ending with Saturday, followed by 1
     bit that is always set to '0'.  For each day of the week, the value
     '1' indicates that the policy is valid for that day, and the value
     '0' indicates that it is not valid.
 
   The value 0x000000057C, for example, indicates that a policy rule is
   valid Monday through Friday.
 
   The property definition is as follows:
 
     NAME             DayOfWeekMask
     DESCRIPTION      A mask identifying the days of the week on which a
                      policy rule is valid.
     SYNTAX           octet string
     FORMAT           0x00000005XX
 
 6.5.5. The Property "TimeOfDayMask"
 
   The purpose of this property is to refine the definition of the valid
   time period that is defined by the TimePeriod property by explicitly
   specifying a range of times in a day the policy is valid for. These
   properties work together, with the TimePeriod used to specify the
   overall time period that the policy is valid for, and the
   TimeOfDayMask used to pick out which range of time periods in a given
   day of that time period the policy is valid for.
 
   This property is formatted in the style of RFC 2445 [10]:  a time
   string beginning with the character 'T', followed by the solidus
   character '/', followed by a second time string.  The first time
   indicates the beginning of the range, while the second time indicates
   the end.  Times are expressed as substrings of the form "Thhmmss".
 
   The second substring always identifies a later time than the first
   substring.  To allow for ranges that span midnight, however, the value
   of the second string may be smaller than the value of the first
   substring.  Thus, "T080000/T210000" identifies the range from 0800
 
 
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   until 2100, while "T210000/T080000" identifies the range from 2100
   until 0800 of the following day.
 
   When a range spans midnight, it by definition includes parts of two
   successive days.  When one of these days is also selected by either
   the MonthOfYearMask, DayOfMonthMask, and/or DayOfWeekMask, but the
   other day is not, then the policy is active only during the portion of
   the range that falls on the selected day.  For example, if the range
   extends from 2100 until 0800, and the day of week mask selects Monday
   and Tuesday, then the policy is active during the following three
   intervals:
 
       From midnight Sunday until 0800 Monday;
       From 2100 Monday until 0800 Tuesday;
       From 2100 Tuesday until 23:59:59 Tuesday.
 
 
   The property definition is as follows:
 
     NAME             TimeOfDayMask
     DESCRIPTION      The range of times at which a policy rule is valid.
                      If the second time is earlier than the first, then
                      the interval spans midnight.
     SYNTAX           string
     FORMAT           Thhmmss/Thhmmss
 
 6.5.6. The Property "LocalOrUtcTime"
 
   This property indicates whether the times represented in the
   TimePeriod property and in the various Mask properties represent local
   times or UTC times.  There is no provision for mixing of local times
   and UTC times:  the value of this property applies to all of the other
   time-related properties.
 
   The property definition is as follows:
 
     NAME             LocalOrUtcTime
     DESCRIPTION      An indication of whether the other times in this
                      instance represent local times or UTC times.
     SYNTAX           uint16
     VALUES           localTime(1), utcTime(2)
     DEFAULT VALUE    utcTime(2)
 
 6.6. The Class "VendorPolicyCondition"
 
   The purpose of this class is to provide a general extension mechanism
   for representing policy conditions that have not been modeled with
   specific properties. Instead, the two properties Constraint and
   ConstraintEncoding are used to define the content and format of the
   condition, as explained below.
 
 
 
 
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   As its name suggests, this class is intended for vendor-specific
   extensions to the Policy Core Information Model.  Standardized
   extensions are not expected to use this class.
 
   The class definition is as follows:
 
     NAME             VendorPolicyCondition
     DESCRIPTION      A class that defines a registered means to describe
                      a policy condition.
     DERIVED FROM     PolicyCondition
     ABSTRACT         FALSE
     PROPERTIES       Constraint[ ]
                      ConstraintEncoding
 
 6.6.1. The Multi-valued Property "Constraint"
 
   This property provides a general extension mechanism for representing
   policy conditions that have not been modeled with specific properties.
   The format of the octet strings in the array is left unspecified in
   this definition.  It is determined by the OID value stored in the
   property ConstraintEncoding.  Since ConstraintEncoding is single-
   valued, all the values of Constraint share the same format and
   semantics.
 
   NOTE:  CIM has a particular way of representing an array of octet
   strings.  (A single octet string can be represented as an ordered
   array of uint8's, but this does not work for multi-valued properties
   where each value is an octet string.)  There is a qualifier
   "Octetstring" that can be applied to a multi-valued string property.
   This qualifier functions exactly like an SMIv2 (SNMP) Textual
   Convention, refining the syntax and semantics of the existing CIM data
   types "string".  Strings with this qualifier consist of a 4-octet
   length field, followed by an even number of the characters A-F and 0-
   9.  The length is encoded as an 8-digit hexadecimal value, which
   includes the 4 octets of the length field itself.  For example, the
   octet string 0x4a is encoded as 0x000000063441.
 
   A policy decision point can readily determine whether it supports the
   values stored in an instance of Constraint by checking the OID value
   from ConstraintEncoding against the set of OIDs it recognizes.  The
   action for the policy decision point to take in case it does not
   recognize the format of this data could itself be modeled as a policy
   rule, governing the behavior of the policy decision point.
 
   The property is defined as follows:
 
     NAME             Constraint
     DESCRIPTION      Extension mechanism for representing constraints
                      that have not been modeled as specific properties.
                      The format of the values is identified by the OID
                      stored in the property ConstraintEncoding.
     SYNTAX           string
     QUALIFIER        Octetstring
 
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 6.6.2. The Property "ConstraintEncoding"
 
   This property identifies the encoding and semantics of the Constraint
   property values in this instance.  The value of this property is a
   single string, representing a single OID.
 
   The property is defined as follows:
 
     NAME             ConstraintEncoding
     DESCRIPTION      An OID encoded as a string, identifying the format
                      and semantics for this instance's Constraint
                      property.  The value is a dotted sequence of
                      decimal digits (for example, "1.2.100.200")
                      representing the arcs of the OID.  The characters
                      in the string are the UCS-2 characters
                      corresponding to the US ASCII encodings of the
                      numeric characters and the period.
     SYNTAX           string
 
 
 
 6.7. The Class "PolicyAction"
 
   The purpose of a policy action is to execute one or more operations
   that will affect network traffic and/or systems, devices, etc. in
   order to achieve a desired state.  This (new) state provides one or
   more (new) behaviors.  A policy action ordinarily changes the
   configuration of one or more elements.
 
   A PolicyRule contains one or more policy actions.  A policy
   administrator can assign an order to the actions associated with a
   PolicyRule, complete with an indication of whether the indicated order
   is mandatory, recommended, or of no significance.  Ordering of the
   actions associated with a PolicyRule is accomplished via a property in
   the PolicyActionInPolicyRule aggregation.
 
   The actions associated with a PolicyRule are executed if and only if
   the overall condition(s) of the PolicyRule evaluates to TRUE.
 
   The class definition of PolicyAction is as follows:
 
     NAME             PolicyAction
     DESCRIPTION      A class representing a rule-specific or reusable
                      policy action to be performed if the condition for
                      a policy rule evaluates to TRUE.
     DERIVED FROM     Policy
     ABSTRACT         FALSE
     PROPERTIES       NONE
 
   No properties are defined for this class since it inherits all its
   properties from Policy.  The class exists as an abstract superclass
   for domain-specific policy actions, defined in subclasses.  In an
 
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   implementation, various key/identification properties MUST be defined
   for the class or its instantiable subclasses.  The keys for a native
   CIM implementation are defined in Appendix A, Section 14.3.  Keys for
   an LDAP implementation are defined in the LDAP mapping of this
   information model [11].
 
   When identifying and using the PolicyAction class, it is necessary to
   remember that an action can be rule-specific or reusable.  This was
   discussed above in Section 5.1. The distinction between the two types
   of policy actions lies in the associations in which an instance can
   participate, and in how the different instances are named.
   Conceptually, a reusable policy action resides in a policy repository,
   and is named within the scope of that repository.  On the other hand,
   a rule-specific policy action is named within the scope of the single
   policy rule to which it is related.
 
   The distinction between rule-specific and reusable PolicyActions
   affects the CIM naming, defined in Appendix A, and the LDAP mapping
   [11].
 
 6.8. The Class "VendorPolicyAction"
 
   The purpose of this class is to provide a general extension mechanism
   for representing policy actions that have not been modeled with
   specific properties. Instead, the two properties ActionData and
   ActionEncoding are used to define the content and format of the
   action, as explained below.
 
   As its name suggests, this class is intended for vendor-specific
   extensions to the Policy Core Information Model.  Standardized
   extensions are not expected to use this class.
 
   The class definition is as follows:
 
     NAME             VendorPolicyAction
     DESCRIPTION      A class that defines a registered means to describe
                      a policy action.
     DERIVED FROM     PolicyAction
     ABSTRACT         FALSE
     PROPERTIES       ActionData[ ]
                      ActionEncoding
 
 6.8.1. The Multi-valued Property "ActionData"
 
   This property provides a general extension mechanism for representing
   policy actions that have not been modeled with specific properties.
   The format of the octet strings in the array is left unspecified in
   this definition.  It is determined by the OID value stored in the
   property ActionEncoding.  Since ActionEncoding is single-valued, all
   the values of ActionData share the same format and semantics.  See
   Section 6.6.1 for a discussion of how CIM encodes an array of octet
   strings.
 
 
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   A policy decision point can readily determine whether it supports the
   values stored in an instance of ActionData by checking the OID value
   from ActionEncoding against the set of OIDs it recognizes.  The action
   for the policy decision point to take in case it does not recognize
   the format of this data could itself be modeled as a policy rule,
   governing the behavior of the policy decision point.
 
   The property is defined as follows:
 
     NAME             ActionData
     DESCRIPTION      Extension mechanism for representing actions that
                      have not been modeled as specific properties. The
                      format of the values is identified by the OID
                      stored in the property ActionEncoding.
     SYNTAX           string
     QUALIFIER        Octetstring
 
 
 6.8.2. The Property "ActionEncoding"
 
   This property identifies the encoding and semantics of the ActionData
   property values in this instance.  The value of this property is a
   single string, representing a single OID.
 
   The property is defined as follows:
 
     NAME             ActionEncoding
     DESCRIPTION      An OID encoded as a string, identifying the format
                      and semantics for this instance's ActionData
                      property.  The value is a dotted sequence of
                      decimal digits (for example, "1.2.100.200")
                      representing the arcs of the OID.  The characters
                      in the string are the UCS-2 characters
                      corresponding to the US ASCII encodings of the
                      numeric characters and the period.
     SYNTAX           string
 
 6.9. The Class "PolicyRepository"
 
   The class definition of PolicyRepository is as follows:
 
     NAME             PolicyRepository
     DESCRIPTION      A class representing an administratively defined
                      container for reusable policy-related information.
                      This class does not introduce any additional
                      properties beyond those in its superclass
                      AdminDomain.  It does, however, participate in a
                      number of unique associations.
     DERIVED FROM     AdminDomain
     ABSTRACT         FALSE
 
 
 
 
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 7. Association and Aggregation Definitions
 
   The first two subsections of this section introduce associations and
   aggregations as they are used in CIM.  The remaining subsections
   present the class definitions for the associations and aggregations
   that are part of the Policy Core Information Model.
 
 7.1. Associations
 
   An association is a CIM construct representing a relationship between
   two (or theoretically more) objects.  It is modeled as a class
   containing typically two object references.  Associations can be
   defined between classes without affecting any of the related classes.
   That is, addition of an association does not affect the interface of
   the related classes.
 
 7.2. Aggregations
 
   An aggregation is a strong form of an association, which usually
   represents a "whole-part" or a "collection" relationship.  For
   example, CIM uses an aggregation to represent the containment
   relationship between a system and the components that make up the
   system.  Aggregation as a "whole-part" relationship often implies, but
   does not require, that the aggregated objects have mutual
   dependencies.
 
 7.3. The Abstract Aggregation "PolicyComponent
 
   This abstract aggregation defines two object references that will be
   overridden in each of five subclasses, to become references to the
   concrete policy classes PolicyGroup, PolicyRule, PolicyCondition,
   PolicyAction, and PolicyTimePeriodCondition.  The value of the
   abstract superclass is to convey that all five subclasses have the
   same "whole-part" semantics, and for ease of query to locate all
   "components" of a PolicyGroup or PolicyRule.
 
   The class definition for the aggregation is as follows:
 
     NAME             PolicyComponent
     DESCRIPTION      A generic aggregation used to establish 'part of'
                      relationships between the subclasses of Policy. For
                      example, the PolicyConditionInPolicyRule
                      aggregation defines that PolicyConditions are part
                      of a PolicyRule.
     ABSTRACT         TRUE
     PROPERTIES       GroupComponent[ref Policy[0..n]]
                      PartComponent[ref Policy[0..n]]
 
 7.4. The Aggregation "PolicyGroupInPolicyGroup"
 
   The PolicyGroupInPolicyGroup aggregation enables policy groups to be
   nested.  This is critical for scalability and manageability, as it
   enables complex policies to be constructed from multiple simpler
 
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   policies for administrative convenience.  For example, a policy group
   representing policies for the US might have nested within it policy
   groups for the Eastern and Western US.
 
   A PolicyGroup may aggregate other PolicyGroups via this aggregation,
   or it may aggregate PolicyRules via the PolicyRuleInPolicyGroup
   aggregation.  But a single PolicyGroup SHALL NOT do both.
 
   The class definition for the aggregation is as follows:
 
     NAME             PolicyGroupInPolicyGroup
     DESCRIPTION      A class representing the aggregation of
                      PolicyGroups by a higher-level PolicyGroup.
     DERIVED FROM     PolicyComponent
     ABSTRACT         FALSE
     PROPERTIES       GroupComponent[ref PolicyGroup[0..n]]
                      PartComponent[ref PolicyGroup[0..n]]
 
 7.4.1. The Reference "GroupComponent"
 
   This property is inherited from PolicyComponent, and overridden to
   become an object reference to a PolicyGroup that contains one or more
   other PolicyGroups.  Note that for any single instance of the
   aggregation class PolicyGroupInPolicyGroup, this property (like all
   Reference properties) is single-valued.  The [0..n] cardinality
   indicates that there may be 0, 1, or more than one PolicyGroups that
   contain any given PolicyGroup.
 
 7.4.2. The Reference "PartComponent"
 
   This property is inherited from PolicyComponent, and overridden to
   become an object reference to a PolicyGroup contained by one or more
   other PolicyGroups.  Note that for any single instance of the
   aggregation class PolicyGroupInPolicyGroup, this property (like all
   Reference properties) is single-valued.  The [0..n] cardinality
   indicates that a given PolicyGroup may contain 0, 1, or more than one
   other PolicyGroups.
 
 7.5. The Aggregation "PolicyRuleInPolicyGroup"
 
   A policy group may aggregate one or more policy rules, via the
   PolicyRuleInPolicyGroup aggregation.  Grouping of policy rules into a
   policy group is again for administrative convenience; a policy rule
   may also be used by itself, without belonging to a policy group.
 
   A PolicyGroup may aggregate PolicyRules via this aggregation, or it
   may aggregate other PolicyGroups via the PolicyGroupInPolicyGroup
   aggregation.  But a single PolicyGroup SHALL NOT do both.
 
   The class definition for the aggregation is as follows:
 
     NAME             PolicyRuleInPolicyGroup
 
 
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     DESCRIPTION      A class representing the aggregation of PolicyRules
                      by a PolicyGroup.
     DERIVED FROM     PolicyComponent
     ABSTRACT         FALSE
     PROPERTIES       GroupComponent[ref PolicyGroup[0..n]]
                      PartComponent[ref PolicyRule[0..n]]
 
 7.5.1. The Reference "GroupComponent"
 
   This property is inherited from PolicyComponent, and overridden to
   become an object reference to a PolicyGroup that contains one or more
   PolicyRules.  Note that for any single instance of the aggregation
   class PolicyRuleInPolicyGroup, this property (like all Reference
   properties) is single-valued.  The [0..n] cardinality indicates that
   there may be 0, 1, or more than one PolicyGroups that contain any
   given PolicyRule.
 
 7.5.2. The Reference "PartComponent"
 
   This property is inherited from PolicyComponent, and overridden to
   become an object reference to a PolicyRule contained by one or more
   PolicyGroups.  Note that for any single instance of the aggregation
   class PolicyRuleInPolicyGroup, this property (like all Reference
   properties) is single-valued.  The [0..n] cardinality indicates that a
   given PolicyGroup may contain 0, 1, or more than one PolicyRules.
 
 7.6. The Aggregation "PolicyConditionInPolicyRule"
 
   A policy rule aggregates zero or more instances of the PolicyCondition
   class, via the PolicyConditionInPolicyRule association.  A policy rule
   that aggregates zero policy conditions is not a valid rule -- it may,
   for example, be in the process of being entered into the policy
   repository.  A policy rule has no effect until it is valid.  The
   conditions aggregated by a policy rule are grouped into two levels of
   lists: either an ORed set of ANDed sets of conditions (DNF, the
   default) or an ANDed set of ORed sets of conditions (CNF).  Individual
   conditions in these lists may be negated.  The property
   ConditionListType (in PolicyRule) specifies which of these two
   grouping schemes applies to a particular PolicyRule.  The conditions
   are used to determine whether to perform the actions associated with
   the PolicyRule.
 
   One or more policy time periods may be among the conditions associated
   with a policy rule via the PolicyConditionInPolicyRule association.
   In this case, the time periods are simply additional conditions to be
   evaluated along with any other conditions specified for the rule.
 
   The class definition for the aggregation is as follows:
 
     NAME             PolicyConditionInPolicyRule
     DESCRIPTION      A class representing the aggregation of
                      PolicyConditions by a PolicyRule.
     DERIVED FROM     PolicyComponent
 
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     ABSTRACT         FALSE
     PROPERTIES       GroupComponent[ref PolicyRule[0..n]]
                      PartComponent[ref PolicyCondition[0..n]]
                      GroupNumber
                      ConditionNegated
 
 7.6.1. The Reference "GroupComponent"
 
   This property is inherited from PolicyComponent, and overridden to
   become an object reference to a PolicyRule that contains one or more
   PolicyConditions.  Note that for any single instance of the
   aggregation class PolicyConditionInPolicyRule, this property (like all
   Reference properties) is single-valued.  The [0..n] cardinality
   indicates that there may be 0, 1, or more than one PolicyRules that
   contain any given PolicyCondition.
 
 7.6.2. The Reference "PartComponent"
 
   This property is inherited from PolicyComponent, and overridden to
   become an object reference to a PolicyCondition contained by one or
   more PolicyRules.  Note that for any single instance of the
   aggregation class PolicyConditionInPolicyRule, this property (like all
   Reference properties) is single-valued.  The [0..n] cardinality
   indicates that a given PolicyRule may contain 0, 1, or more than one
   PolicyConditions.
 
 7.6.3. The Property "GroupNumber"
 
   This property contains an integer identifying the group to which the
   condition referenced by the PartComponent property is assigned in
   forming the overall conditional expression for the policy rule
   identified by the GroupComponent reference.
 
   The property is defined as follows:
 
     NAME             GroupNumber
     DESCRIPTION      Unsigned integer indicating the group to which the
                      condition identified by the PartComponent property
                      is to be assigned.
     SYNTAX           uint16
 
 
 7.6.4. The Property "ConditionNegated"
 
   This property is a boolean, indicating whether the condition
   referenced by the PartComponent property is negated in forming the
   overall conditional expression for the policy rule identified by the
   GroupComponent reference.
 
   The property is defined as follows:
 
     NAME             ConditionNegated
 
 
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     DESCRIPTION      Indication of whether the condition identified by
                      the PartComponent property is negated.  (TRUE
                      indicates that the condition is negated, FALSE
                      indicates that it is not negated.)
     SYNTAX           boolean
 
 
 7.7. The Aggregation "PolicyRuleValidityPeriod"
 
   A different relationship between a policy rule and a policy time
   period (than PolicyConditionInPolicyRule) is represented by the
   PolicyRuleValidityPeriod aggregation. The latter describes scheduled
   activation and deactivation of the policy rule.
 
   If a policy rule is associated with multiple policy time periods via
   this association, then the rule is active if at least one of the time
   periods indicates that it is active.  (In other words, the time
   periods are ORed to determine whether the rule is active.)  A policy
   time period may be aggregated by multiple policy rules.  A rule that
   does not point to a policy time period via this aggregation is, from
   the point of view of scheduling, always active.  It may, however, be
   inactive for other reasons.
 
   Time periods are a general concept that can be used in other
   applications. However, they are mentioned explicitly here in this
   specification since they are frequently used in policy applications.
 
   The class definition for the aggregation is as follows:
 
     NAME             PolicyRuleValidityPeriod
     DESCRIPTION      A class representing the aggregation of
                      PolicyTimePeriodConditions by a PolicyRule.
     DERIVED FROM     PolicyComponent
     ABSTRACT         FALSE
     PROPERTIES       GroupComponent[ref PolicyRule[0..n]]
                      PartComponent[ref PolicyTimePeriodCondition[0..n]]
 
 7.7.1. The Reference "GroupComponent"
 
   This property is inherited from PolicyComponent, and overridden to
   become an object reference to a PolicyRule that contains one or more
   PolicyTimePeriodConditions.  Note that for any single instance of the
   aggregation class PolicyRuleValidityPeriod, this property (like all
   Reference properties) is single-valued.  The [0..n] cardinality
   indicates that there may be 0, 1, or more than one PolicyRules that
   contain any given PolicyTimePeriodCondition.
 
 7.7.2. The Reference "PartComponent"
 
   This property is inherited from PolicyComponent, and overridden to
   become an object reference to a PolicyTimePeriodCondition contained by
   one or more PolicyRules.  Note that for any single instance of the
   aggregation class PolicyRuleValidityPeriod, this property (like all
 
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   Reference properties) is single-valued.  The [0..n] cardinality
   indicates that a given PolicyRule may contain 0, 1, or more than one
   PolicyTimePeriodConditions.
 
 
 7.8. The Aggregation "PolicyActionInPolicyRule"
 
   A policy rule may aggregate zero or more policy actions.  A policy
   rule that aggregates zero policy actions is not a valid rule -- it
   may, for example, be in the process of being entered into the policy
   repository.  A policy rule has no effect until it is valid.  The
   actions associated with a PolicyRule may be given a required order, a
   recommended order, or no order at all. For actions represented as
   separate objects, the PolicyActionInPolicyRule aggregation can be used
   to express an order.
 
   This aggregation does not indicate whether a specified action order is
   required, recommended, or of no significance; the property
   SequencedActions in the aggregating instance of PolicyRule provides
   this indication.
 
   The class definition for the aggregation is as follows:
 
     NAME             PolicyActionInPolicyRule
     DESCRIPTION      A class representing the aggregation of
                      PolicyActions by a PolicyCondition.
     DERIVED FROM     PolicyComponent
     ABSTRACT         FALSE
     PROPERTIES       GroupComponent[ref PolicyRule[0..n]]
                      PartComponent[ref PolicyAction[0..n]]
                      ActionOrder
 
 
 7.8.1. The Reference "GroupComponent"
 
   This property is inherited from PolicyComponent, and overridden to
   become an object reference to a PolicyRule that contains one or more
   PolicyActions.  Note that for any single instance of the aggregation
   class PolicyActionInPolicyRule, this property (like all Reference
   properties) is single-valued.  The [0..n] cardinality indicates that
   there may be 0, 1, or more than one PolicyRules that contain any given
   PolicyAction.
 
 7.8.2. The Reference "PartComponent"
 
   This property is inherited from PolicyComponent, and overridden to
   become an object reference to a PolicyAction contained by one or more
   PolicyRules.  Note that for any single instance of the aggregation
   class PolicyActionInPolicyRule, this property (like all Reference
   properties) is single-valued.  The [0..n] cardinality indicates that a
   given PolicyRule may contain 0, 1, or more than one  PolicyActions.
 
 
 
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 7.8.3. The Property "ActionOrder"
 
   This property provides an unsigned integer 'n' that indicates the
   relative position of an action in the sequence of actions associated
   with a policy rule.  When 'n' is a positive integer, it indicates a
   place in the sequence of actions to be performed, with smaller
   integers indicating earlier positions in the sequence.  The special
   value '0' indicates "don't care".  If two or more actions have the
   same non-zero sequence number, they may be performed in any order, but
   they must all be performed at the appropriate place in the overall
   action sequence.
 
   A series of examples will make ordering of actions clearer:
 
   o If all actions have the same sequence number, regardless of whether
     it is '0' or non-zero, any order is acceptable.
 
   o The values
 
     1:ACTION A
     2:ACTION B
     1:ACTION C
     3:ACTION D
 
     indicate two acceptable orders:  A,C,B,D or C,A,B,D, since A and C
     can be performed in either order, but only at the '1' position.
 
   o The values
 
     0:ACTION A
     2:ACTION B
     3:ACTION C
     3:ACTION D
 
     require that B,C, and D occur either as B,C,D or as B,D,C.  Action
     A may appear at any point relative to B,C, and D.  Thus the
     complete set of acceptable orders is:  A,B,C,D; B,A,C,D; B,C,A,D;
     B,C,D,A; A,B,D,C; B,A,D,C; B,D,A,C; B,D,C,A.
 
   Note that the non-zero sequence numbers need not start with '1', and
   they need not be consecutive.  All that matters is their relative
   magnitude.
 
   The property is defined as follows:
 
     NAME             ActionOrder
     DESCRIPTION      Unsigned integer indicating the relative position
                      of an action in the sequence of actions aggregated
                      by a policy rule.
     SYNTAX           uint16
 
 
 
 
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 7.9. The Abstract Association "PolicyInSystem"
 
   This abstract association inherits two object references from a
   higher-level CIM association class, Dependency.  It overrides these
   object references to make them references to instances of the classes
   System and Policy.  Subclasses of PolicyInSystem then override these
   object references again, to make them references to concrete policy
   classes.
 
   The value of the abstract superclass is to convey that all subclasses
   have the same "dependency" semantics, and for ease of query to locate
   all policy "dependencies" on a System.  These dependencies are related
   to scoping or hosting of the Policy.
 
   The class definition for the association is as follows:
 
     NAME             PolicyInSystem
     DESCRIPTION      A generic association used to establish dependency
                      relationships between Policies and the Systems that
                      host them.
     DERIVED FROM     Dependency
     ABSTRACT         TRUE
     PROPERTIES       Antecedent[ref System[0..1]]
                      Dependent[ref Policy[0..n]]
 
 
 7.10. The Weak Association "PolicyGroupInSystem"
 
   This association links a PolicyGroup to the System in whose scope the
   PolicyGroup is defined.
 
   The class definition for the association is as follows:
 
     NAME             PolicyGroupInSystem
     DESCRIPTION      A class representing the fact that a PolicyGroup is
                      defined within the scope of a System.
     DERIVED FROM     PolicyInSystem
     ABSTRACT         FALSE
     PROPERTIES       Antecedent[ref System[1..1]]
                      Dependent[ref PolicyGroup[weak]]
 
 7.10.1. The Reference "Antecedent"
 
   This property is inherited from PolicyInSystem, and overridden to
   restrict its cardinality to [1..1].  It serves as an object reference
   to a System that provides a scope for one or more PolicyGroups.  Since
   this is a weak association, the cardinality for this object reference
   is always 1, that is, a PolicyGroup is always defined within the scope
   of exactly one System.
 
 
 
 
 
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 7.10.2. The Reference "Dependent"
 
   This property is inherited from PolicyInSystem, and overridden to
   become an object reference to a PolicyGroup defined within the scope
   of a System.  Note that for any single instance of the association
   class PolicyGroupInSystem, this property (like all Reference
   properties) is single-valued.  The [0..n] cardinality indicates that a
   given System may have 0, 1, or more than one PolicyGroups defined
   within its scope.
 
 7.11. The Weak Association "PolicyRuleInSystem"
 
   Regardless of whether it belongs to a PolicyGroup (or to multiple
   PolicyGroups), a PolicyRule is itself defined within the scope of a
   System.  This association links a PolicyRule to the System in whose
   scope the PolicyRule is defined.
 
   The class definition for the association is as follows:
 
     NAME             PolicyRuleInSystem
     DESCRIPTION      A class representing the fact that a PolicyRule is
                      defined within the scope of a System.
     DERIVED FROM     PolicyInSystem
     ABSTRACT         FALSE
     PROPERTIES       Antecedent[ref System[1..1]]
                      Dependent[ref PolicyRule[weak]]
 
 7.11.1. The Reference "Antecedent"
 
   This property is inherited from PolicyInSystem, and overridden to
   restrict its cardinality to [1..1].  It serves as an object reference
   to a System that provides a scope for one or more PolicyRules.  Since
   this is a weak association, the cardinality for this object reference
   is always 1, that is, a PolicyRule is always defined within the scope
   of exactly one System.
 
 7.11.2. The Reference "Dependent"
 
   This property is inherited from PolicyInSystem, and overridden to
   become an object reference to a PolicyRule defined within the scope of
   a System.  Note that for any single instance of the association class
   PolicyRuleInSystem, this property (like all Reference properties) is
   single-valued.  The [0..n] cardinality indicates that a given System
   may have 0, 1, or more than one PolicyRules defined within its scope.
 
 7.12. The Association "PolicyConditionInPolicyRepository"
 
   A reusable policy condition is always related to a single
   PolicyRepository, via the PolicyConditionInPolicyRepository
   association.  This is not true for all PolicyConditions, however.  An
   instance of PolicyCondition that represents a rule-specific condition
   is not related to any policy repository via this association.
 
 
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   The class definition for the association is as follows:
 
     NAME             PolicyConditionInPolicyRepository
     DESCRIPTION      A class representing the inclusion of a reusable
                      PolicyCondition in a PolicyRepository.
     DERIVED FROM     PolicyInSystem
     ABSTRACT         FALSE
     PROPERTIES       Antecedent[ref PolicyRepository[0..1]]
                      Dependent[ref PolicyCondition[0..n]]
 
 7.12.1. The Reference "Antecedent"
 
   This property is inherited from PolicyInSystem, and overridden to
   become an object reference to a PolicyRepository containing one or
   more PolicyConditions.  A reusable PolicyCondition is always related
   to exactly one PolicyRepository via the
   PolicyConditionInPolicyRepository association.  The [0..1] cardinality
   for this property covers the two types of PolicyConditions:  0 for a
   rule-specific PolicyCondition, 1 for a reusable one.
 
 7.12.2. The Reference "Dependent"
 
   This property is inherited from PolicyInSystem, and overridden to
   become an object reference to a PolicyCondition included in a
   PolicyRepository.  Note that for any single instance of the
   association class PolicyConditionInPolicyRepository, this property
   (like all Reference properties) is single-valued.  The [0..n]
   cardinality indicates that a given PolicyRepository may contain 0, 1,
   or more than one PolicyConditions.
 
 7.13. The Association "PolicyActionInPolicyRepository"
 
   A reusable policy action is always related to a single
   PolicyRepository, via the PolicyActionInPolicyRepository association.
   This is not true for all PolicyActions, however.  An instance of
   PolicyAction that represents a rule-specific action is not related to
   any policy repository via this association.
 
   The class definition for the association is as follows:
 
     NAME             PolicyActionInPolicyRepository
     DESCRIPTION      A class representing the inclusion of a reusable
                      PolicyAction in a PolicyRepository.
     DERIVED FROM     PolicyInSystem
     ABSTRACT         FALSE
     PROPERTIES       Antecedent[ref PolicyRepository[0..1]]
                      Dependent[ref PolicyAction[0..n]]
 
 7.13.1. The Reference "Antecedent"
 
   This property is inherited from PolicyInSystem, and overridden to
   become an object reference to a PolicyRepository containing one or
   more PolicyActions.  A reusable PolicyAction is always related to
 
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   exactly one PolicyRepository via the PolicyActionInPolicyRepository
   association.  The [0..1] cardinality for this property covers the two
   types of PolicyActions:  0 for a rule-specific PolicyAction, 1 for a
   reusable one.
 
 7.13.2. The Reference "Dependent"
 
   This property is inherited from PolicyInSystem, and overridden to
   become an object reference to a PolicyAction included in a
   PolicyRepository.  Note that for any single instance of the
   association class PolicyActionInPolicyRepository, this property (like
   all Reference properties) is single-valued.  The [0..n] cardinality
   indicates that a given PolicyRepository may contain 0, 1, or more than
   one PolicyActions.
 
 7.14. The Aggregation "PolicyRepositoryInPolicyRepository"
 
   The PolicyRepositoryInPolicyRepository aggregation enables policy
   repositories to be nested.  This derives from the higher level CIM
   association, CIM_SystemComponent, describing that Systems contain
   other ManagedSystemElements.  This superclass could not be used for
   the other Policy aggregations, since Policies are not
   ManagedSystemElements, but ManagedElements.
 
   The class definition for the aggregation is as follows:
 
     NAME             PolicyRepositoryInPolicyRepository
     DESCRIPTION      A class representing the aggregation of
                      PolicyRepositories by a higher-level
                      PolicyRepository.
     DERIVED FROM     SystemComponent
     ABSTRACT         FALSE
     PROPERTIES       GroupComponent[ref PolicyRepository[0..n]]
                      PartComponent[ref PolicyRepository[0..n]]
 
 7.14.1. The Reference "GroupComponent"
 
   This property is inherited from the CIM class SystemComponent, and
   overridden to become an object reference to a PolicyRepository that
   contains one or more other PolicyRepositories.  Note that for any
   single instance of the aggregation class
   PolicyRepositoryInPolicyRepository, this property (like all Reference
   properties) is single-valued.  The [0..n] cardinality indicates that
   there may be 0, 1, or more than one PolicyRepositories that contain
   any given PolicyRepository.
 
 7.14.2. The Reference "PartComponent"
 
   This property is inherited from the CIM class SystemComponent, and
   overridden to become an object reference to a PolicyRepository
   contained by one or more other PolicyRepositories.  Note that for any
   single instance of the aggregation class
   PolicyRepositoryInPolicyRepository, this property (like all Reference
 
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   properties) is single-valued.  The [0..n] cardinality indicates that a
   given PolicyRepository may contain 0, 1, or more than one other
   PolicyRepositories.
 
 
 8. Intellectual Property
 
   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to pertain
   to the implementation or use of the technology described in this
   document or the extent to which any license under such rights might or
   might not be available; neither does it represent that it has made any
   effort to identify any such rights.  Information on the IETF's
   procedures with respect to rights in standards-track and standards-
   related documentation can be found in BCP-11.
 
   Copies of claims of rights made available for publication and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this specification
   can be obtained from the IETF Secretariat.
 
   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights which may cover technology that may be required to practice
   this standard.  Please address the information to the IETF Executive
   Director.
 
 
 9. Acknowledgements
 
   The Policy Core Information Model in this document is closely based on
   the work of the DMTF's Service Level Agreements working group, so
   thanks are due to the members of that working group.  Several of the
   policy classes in this model first appeared in early drafts on IPSec
   policy and QoS policy.  The authors of these drafts were Partha
   Bhattacharya, Rob Adams, William Dixon, Roy Pereira, Raju Rajan, Jean-
   Christophe Martin, Sanjay Kamat, Michael See, Rajiv Chaudhury, Dinesh
   Verma, George Powers, and Raj Yavatkar.
 
 
 10. Security Considerations
 
   o  This document itself does not introduce any new security issues for
      the Internet, similar to the circumstances which existed when SMI
      was introduced.  However, it is necessary to document the
      requirements for a secure policy system, in order to show that the
      overall policy framework is viable.  Our model for documenting
      these requirements is based on prior work in the IETF on DNSSEC and
      SNMPv3.  One of our objectives in the policy work in the IETF is to
      not break the known existing security mechanisms, or to make them
      less effective, regardless of whether or not these security
      mechanisms affect what flows on the wire.
 
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   o  Users:  The first step in identifying security requirements for
      policy, is to identify the users of policy.  The users fall into
      three categories:
 
   o  Administrators of Schema: This group requires the most stringent
      authorization and associated security controls.  An improper or
      mal-formed change in the design of the policy schema carries with
      it the danger of rendering the repository inoperable while the
      repository is being repaired or re-built.  During this time, the
      policy enforcement entities would need to continue to enforce
      policies according to their prior configuration. The good news is
      that it is expected that large network operators will change schema
      design infrequently, and, when they do, the schema creation changes
      will be tested on an off-line copy of the directory before the
      operational directory is updated.  Typically, a small group of
      schema administrators will be authorized to make these changes in a
      service provider or enterprise environment.  The ability to
      maintain an audit trail is also required here.
 
   o  Administrators of Schema Content: This group requires authorization
      to load values (entries) into a policy repository) schema
      (read/write access).   An audit trail mechanism is also required
      here. The effect of entering improperly formatted or maliciously-
      intended data into a policy repository, could potentially result in
      re-configuring mass numbers of network elements in a way that
      renders them to be inoperable, or of rendering network resources
      inaccessible for an extended period of time.
 
   o  Applications and PDPs:  These entities must be authorized for read-
      only access to the policy repository, so that they may acquire
      policy for the purposes of passing it to their respective
      enforcement entities.
 
   o  Security Disciplines:
 
        o  Audit Trail (Non-repudiation):  We document the need for this
           function in systems which maintain and distribute policy.  The
           dependency for support of this function is on the implementers
           of these systems, and not on any specific standards for
           implementation.  The requirement for a policy system is that a
           minimum level of auditing via an auditing facility must be
           provided.  Logging should be enabled.  This working group will
           not specify what this minimal auditing function consists of.
 
        o  Access Control/Authorization:  Access Control List (ACL)
           functionality must be provided. The two administrative sets of
           users documented above will form the basis for two
           administrative use cases which require support.
 
        o  Authentication:  Authentication support on the order of that
           available with  TLS and Kerberos are acceptable for
           authentication.  We advise against using weaker mechanisms,
 
 
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           such as clear text and HTTP Digest.  Mutual authentication is
           recommended.
 
        o  Integrity/Privacy:  Integrity/privacy support on the order of
           TLS  or IPSec is acceptable for encryption and data integrity
           on the wire.  If physical or virtual access to the policy
           repository is in question, it may also be necessary to encrypt
           the policy data as it is stored on the file system; however,
           specification of mechanisms for this purpose are outside the
           scope of this working group.  In any case, we recommend that
           the physical server be located in a physically secure
           environment.
 
      In the case of PDP-to-PEP communications, the use of IPSec is
      recommended for providing confidentiality, data origin
      authentication, integrity and replay prevention.  See reference
      [9].
 
   o  Denial of Service:  We recommend the use of multiple policy
      repositories, such that a denial of service attack on any one
      repository will not make all policy data inaccessible to legitimate
      users.  However, this still leaves a denial of service attack
      exposure.  Our belief is that the use of a policy schema, in a
      centrally administered but physically distributed policy
      repository, does not increase the risk of denial of service
      attacks; however, such attacks are still possible.  If executed
      successfully, such an attack could prevent PDPs from accessing a
      policy repository, and thus prevent them from acquiring new policy.
      In such a case, the PDPs, and associated PEPs would continue
      operating under the policies in force before the denial of service
      attack was launched.  Note that exposure of policy systems to
      denial of service attacks is not any greater than the exposure of
      DNS with DNSSEC in place.
 
 
 11. References
 
 [1]  Distributed Management Task Force, Inc., "DMTF Technologies:  CIM
      Standards", available via links on the following DMTF web page:
      http://www.dmtf.org/spec/cims.html.
 
 [2]  Distributed Management Task Force, Inc., "Common Information Model
      (CIM) Specification, version 2.2, June 14, 1999.  This document is
      available on the following DMTF web page:
      http://www.dmtf.org/spec/cims.html.
 
 [3]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997.
 
 [4]  Hovey, R., and S. Bradner, "The Organizations Involved in the IETF
      Standards Process", BCP 11, RFC 2028, October 1996.
 
 
 
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 [5]  J. Strassner and S. Judd, "Directory-Enabled Networks", version
      3.0c5 (August 1998).  A PDF file is available at
      http://www.murchiso.com/den/#denspec.
 
 [6]  J. Strassner, policy architecture BOF presentation, 42nd IETF
      Meeting, Chicago, Illinois, October, 1998.  Minutes of this BOF are
      available at the following location:
      http://www.ietf.org/proceedings/98aug/index.html.
 
 [7]  Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC
      2279, January 1998.
 
 [8]  Levi, D., and J. Schoenwaelder, "Definitions of Managed Objects for
      Scheduling Management Operations", RFC 2591, May 1999.
 
 [9]  R. Yavatkar and D. Pendarakis, R. Guerin, "A Framework for Policy-
      based Admission Control", RFC 2753, January 2000.
 
 [10] Dawson, F., and D. Stenerson, "Internet Calendaring and Scheduling
      Core Object Specification (iCalendar)", RFC 2445, November 1998.
 
 [11] Strassner, J., and E. Ellesson, B. Moore, R. Moats, "Policy Core
      LDAP Schema", draft-ietf-policy-core-schema-07.txt, July 2000.
 
 
 12. Authors' Addresses
 
   Ed Ellesson
      Tivoli Systems
      Building 10, Office R2D39
      3901 Miami Blvd.
      Durham, NC 27703
      Phone:   +1 919-224-2111
      Fax:     +1 919-224-2540
      E-mail:  ed_ellesson@tivoli.com
 
   Bob Moore
      IBM Corporation, BRQA/502
      4205 S. Miami Blvd.
      Research Triangle Park, NC 27709
      Phone:   +1 919-254-4436
      Fax:     +1 919-254-6243
      E-mail:  remoore@us.ibm.com
 
   John Strassner
       Cisco Systems, Bldg 15
       170 West Tasman Drive
       San Jose, CA 95134
       Phone:   +1 408-527-1069
       Fax:     +1 408-527-6351
       E-mail:  johns@cisco.com
 
   Andrea Westerinen
 
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       Cisco Systems
       170 West Tasman Drive
       San Jose, CA 95134
       Phone:   +1 408-853-8294
       Fax:     +1 408-527-6351
       E-mail:  andreaw@cisco.com
 
 
 13. Full Copyright Statement
 
   Copyright (C) The Internet Society (2000).  All Rights Reserved.
 
   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published and
   distributed, in whole or in part, without restriction of any kind,
   provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of developing
   Internet standards in which case the procedures for copyrights defined
   in the Internet Standards process must be followed, or as required to
   translate it into languages other than English.
 
   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.
 
   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT
   NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN
   WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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 14. Appendix A - Class Identification in a Native CIM Implementation
 
   While the CommonName property is present in the abstract superclass
   Policy, and is thus available in all of its instantiable subclasses,
   CIM does not use this property for naming instances.  The following
   subsections discuss how naming is handled in a native CIM
   implementation for each of the instantiable classes in the Policy Core
   Information Model.
 
   Two things should be noted regarding CIM naming:
 
   o  When a CIM association is specified as "weak", this is a statement
      about naming scopes:  an instance of the class at the weak end of
      the association is named within the scope of an instance of the
      class at the other end of the association.  This is accomplished by
      propagation of keys from the instance of the scoping class to the
      instance of the weak class.  Thus the weak class has, via key
      propagation, all the keys from the scoping class, and it also has
      one or more additional keys for distinguishing instances of the
      weak class, within the context of the scoping class.
 
   o  All class names in CIM are limited to alphabetic and numeric
      characters plus the underscore, with the restriction that the first
      character cannot be numeric.  Refer to Appendix F "Unicode Usage"
      in reference [2] for an exact specification of how CIM class names
      are encoded in CIM strings.
 
 14.1. Naming Instances of PolicyGroup and PolicyRule
 
   A policy group always exists in the context of a system.  In the
   Policy Core Information Model, this is captured by the weak
   aggregation PolicyGroupInSystem between a PolicyGroup and a System.
   Note that System serves as the base class for describing network
   devices and administrative domains.
 
   A policy rule also exists in the context of a system.  In the Policy
   Core Information Model, this is captured by the weak association
   PolicyRuleInSystem between a PolicyRule and a System.
 
   The following sections define the CIM keys for PolicyGroup and
   PolicyRule.
 
 14.1.1. PolicyGroup's CIM Keys
 
   The CIM keys of the PolicyGroup class are:
 
    o  SystemCreationClassName (A CIM_System key, propagated due to the
       weak association, PolicyGroupInSystem)
    o  SystemName (A CIM_System key, propagated due to  the weak
       association, PolicyGroupInSystem)
    o  CreationClassName
    o  PolicyGroupName
 
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   They are defined in Reference [1] as follows:
 
     NAME             SystemCreationClassName
     DESCRIPTION      SystemCreationClassName represents the class name
                      of the CIM System object providing the naming scope
                      for the instance of PolicyGroup.
     SYNTAX           string [MaxLen 256]
     QUALIFIER        key
 
     NAME             SystemName
     DESCRIPTION      SystemName represent the individual name of the
                      particular System object, providing the naming
                      scope for the instance of PolicyGroup.
     SYNTAX           string [MaxLen 256]
     QUALIFIER        key
 
     NAME             CreationClassName
     DESCRIPTION      This property is set to "CIM_PolicyGroup", if the
                      PolicyGroup object is directly instantiated.  Or,
                      it is equal to the class name of the PolicyGroup
                      subclass that is instantiated.
     SYNTAX           string [MaxLen 256]
     QUALIFIER        key
 
     NAME             PolicyGroupName
     DESCRIPTION      The identifying name of this policy group.
     SYNTAX           string [MaxLen 256]
     QUALIFIER        key
 
 14.1.2. PolicyRule's CIM Keys
 
   The CIM keys of the PolicyRule class are:
 
    o  SystemCreationClassName (A CIM_System key, propagated due to the
       weak association PolicyRuleInSystem)
    o  SystemName (A CIM_System key, propagated due to the weak
       association PolicyRuleInSystem)
    o  CreationClassName
    o  PolicyRuleName
 
   SystemCreationClassName and SystemName work the same as defined for
   the class PolicyGroup.  See Section 14.1.1 for details.
 
   The other two properties are defined in Reference [1] as follows:
 
     NAME             CreationClassName
     DESCRIPTION      This property is set to "CIM_PolicyRule", if the
                      PolicyRule object is directly instantiated.  Or, it
                      is equal to the class name of the PolicyRule
                      subclass that is instantiated.
     SYNTAX           string [MaxLen 256]
     QUALIFIER        key
 
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     NAME             PolicyRuleName
     DESCRIPTION      The identifying name of this policy rule.
     SYNTAX           string [MaxLen 256]
     QUALIFIER        key
 
 14.2. Naming Instances of PolicyCondition and Its Subclasses
 
   The CIM keys of the PolicyCondition class are:
 
     o SystemCreationClassName
     o SystemName
     o PolicyRuleCreationClassName
     o PolicyRuleName
     o CreationClassName
     o PolicyConditionName
 
   Note that none of the keys are defined as propagated, although they
   appear to fit this convention.  The reason for this difference is
   because (as indicated in Sections 5.1 and 6.4) the PolicyCondition
   class is used to represent both reusable and rule-specific conditions.
   This, in turn, affects what associations are valid for an instance of
   PolicyCondition, and how that instance is named.
 
   In an ideal world, an instance of the PolicyCondition class would be
   scoped either by its PolicyRepository (for a reusable condition) or by
   its PolicyRule (for a rule-specific condition).  However, CIM has the
   restriction that a given class can only be "weak" to one other class
   (i.e., defined by one weak association).
 
   To work within the restrictions of CIM naming, it is necessary to
   "simulate" weak associations between PolicyCondition and PolicyRule,
   and between PolicyCondition and PolicyRepository, through a technique
   we'll call manual key propagation.  Strictly speaking, manual key
   propagation isn't key propagation at all.  But it has the same effect
   as (true) key propagation, so the name fits.
 
   Figure 9 illustrates how manual propagation works in the case of
   PolicyCondition. (Note that only the key properties are shown for each
   of the classes.)  In the figure, the line composed of 'I's indicates
   class inheritance, the one composed of 'P's indicates (true) key
   propagation via the weak aggregation PolicyRuleInSystem, and the ones
   composed of 'M's indicate manual key propagation.
 
 
 
 
 
 
 
 
 
 
 
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       +------------------+
       |      System      |
       +------------------+
       |CreationClassName |
       |Name              |
       +------------------+
                 ^     P
                 I     PPPPPPPPPPPPPPPPPPPPPPPPPPPP
                 I                                P
       +------------------+       +---------------v--------------+
       |    AdminDomain   |       |         PolicyRule           |
       +------------------+       +------------------------------+
       |CreationClassName |       | System.CreationClassName     |
       |Name              |       | System.Name                  |
       +------------------+       | CreationClassName            |
                 ^                | PolicyRuleName               |
                 I                +------------------------------+
                 I                         M
                 I                         M
       +------------------+                M
       | PolicyRepository |                M
       +------------------+                M
       |CreationClassName |                M
       |Name              |                M
       +------------------+                M
                       M                   M
                       M                   M
                       M                   M
                  +----v-------------------v----+
                  |       PolicyCondition       |
                  +-----------------------------+
                  | SystemCreationClassName     |
                  | SystemName                  |
                  | PolicyRuleCreationClassName |
                  | PolicyRuleName              |
                  | CreationClassName           |
                  | PolicyConditionName         |
                  +-----------------------------+
 
 
   Figure 9.       Manual Key Propagation for Naming PolicyConditions
 
   Looking at Figure 9, we see that two key properties, CreationClassName
   and Name, are defined in the System class, and inherited by its
   subclasses AdminDomain and PolicyRepository.  Since PolicyRule is weak
   to System, these two keys are propagated to it; it also has its own
   keys CreationClassName and PolicyRuleName.
 
   A similar approach, though not automatic, is used in "manual key
   propagation."  Here is the approach for rule-specific and reusable
   PolicyConditions:
 
 
 
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   o  The manual propagation of keys from PolicyRule to PolicyCondition
      involves copying the values of PolicyRule's four key properties
      into four similarly named key properties in PolicyCondition.  From
      the point of view of the CIM specification language, the property
      SystemName in PolicyCondition is a completely new key property.
      However, the relationship to the Name property in System is defined
      in the description of SystemName.
 
   o  The manual propagation of keys from PolicyRepository to
      PolicyCondition works in exactly the same way for the first two key
      properties.  However, since PolicyRepository doesn't include
      PolicyRule properties, the PolicyRuleCreationClassName and
      PolicyRuleName have no values.  A special value, "No Rule", is
      assigned to both of these properties in this case, indicating that
      this instance of PolicyCondition is not named within the scope of
      any particular policy rule.
 
   The following section defines the specific CIM keys for
   PolicyCondition.
 
 14.2.1. PolicyCondition's CIM Keys
 
   PolicyCondition's key properties are defined in Reference [1] as
   follows:
 
     NAME             SystemCreationClassName
     DESCRIPTION      SystemCreationClassName represents the class name
                      of the CIM System object providing the naming scope
                      for the instance of PolicyCondition.  For a rule-
                      specific policy condition, this is the type of
                      system (e.g., the name of the class that created
                      this instance) in whose context the policy rule is
                      defined.  For a reusable policy condition, this is
                      set to "CIM_PolicyRepository", if the
                      PolicyRepository object is directly instantiated.
                      Or, it is equal to the class name of the
                      PolicyRepository subclass that is instantiated.
     SYNTAX           string [MaxLen 256]
     QUALIFIER        key
 
     NAME             SystemName
     DESCRIPTION      The name of the System object in whose scope this
                      policy condition is defined. This property
                      completes the identification of the System object.
                      For a rule-specific policy condition, this is the
                      name of the instance of the system in whose context
                      the policy rule is defined.  For a reusable policy
                      condition, this is name of the instance of
                      PolicyRepository that holds the policy condition.
     SYNTAX           string [MaxLen 256]
     QUALIFIER        key
 
     NAME             PolicyRuleCreationClassName
 
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     DESCRIPTION      For a rule-specific policy condition, this property
                      identifies the class name of the policy rule
                      instance, in whose scope this instance of
                      PolicyCondition exists.  For a reusable policy
                      condition, this property is set to a special value,
                      "No Rule", indicating that this instance of
                      PolicyCondition is not unique to one policy rule.
     SYNTAX           string [MaxLen 256]
     QUALIFIER        key
 
     NAME             PolicyRuleName
     DESCRIPTION      For a rule-specific policy condition,
                      PolicyRuleName completes the identification of the
                      PolicyRule object with which this condition is
                      associated.  For a reusable policy condition, a
                      special value, "No Rule", is used to indicate that
                      this condition is reusable.
     SYNTAX           string [MaxLen 256]
     QUALIFIER        key
 
     NAME             CreationClassName
     DESCRIPTION      The class name of the PolicyCondition subclass that
                      is instantiated.
     SYNTAX           string [MaxLen 256]
     QUALIFIER        key
 
     NAME             PolicyConditionName
     DESCRIPTION      The identifying name of this policy condition.
     SYNTAX           string [MaxLen 256]
     QUALIFIER        key
 
 14.3. Naming Instances of PolicyAction and Its Subclasses
 
   From the point of view of naming, the PolicyAction class and its
   subclasses work exactly like the PolicyCondition class and its
   subclasses.  See Section 14.2 and 14.2.1 for details.
 
   Specifically, the CIM keys of PolicyAction are:
 
     o SystemCreationClassName
     o SystemName
     o PolicyRuleCreationClassName
     o PolicyRuleName
     o CreationClassName
     o PolicyActionName
 
   They are defined in Reference [1] as follows:
 
     NAME             SystemCreationClassName
     DESCRIPTION      SystemCreationClassName represents the class name
                      of the CIM System object providing the naming scope
                      for the instance of PolicyAction.  For a rule-
                      specific policy action, this is the type of system
 
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                      (e.g., the name of the class that created this
                      instance) in whose context the policy rule is
                      defined.  For a reusable policy action, this is set
                      to "CIM_PolicyRepository", if the PolicyRepository
                      object is directly instantiated.  Or, it is equal
                      to the class name of the PolicyRepository subclass
                      that is instantiated.
     SYNTAX           string [MaxLen 256]
     QUALIFIER        key
 
     NAME             SystemName
     DESCRIPTION      The name of the System object in whose scope this
                      policy action is defined. This property completes
                      the identification of the System object.  For a
                      rule-specific policy action, this is the name of
                      the instance of the system in whose context the
                      policy rule is defined.  For a reusable policy
                      action, this is name of the instance of
                      PolicyRepository that holds the policy action.
     SYNTAX           string [MaxLen 256]
     QUALIFIER        key
 
     NAME             PolicyRuleCreationClassName
     DESCRIPTION      For a rule-specific policy action, this property
                      identifies the class name of the policy rule
                      instance, in whose scope this instance of
                      PolicyAction exists.  For a reusable policy action,
                      this property is set to a special value, "No Rule",
                      indicating that this instance of PolicyAction is
                      not unique to one policy rule.
     SYNTAX           string [MaxLen 256]
     QUALIFIER        key
 
     NAME             PolicyRuleName
     DESCRIPTION      For a rule-specific policy action, PolicyRuleName
                      completes the identification of the PolicyRule
                      object with which this action is associated.  For a
                      reusable policy action, a special value, "No Rule",
                      is used to indicate that this action is reusable.
     SYNTAX           string [MaxLen 256]
     QUALIFIER        key
 
     NAME             CreationClassName
     DESCRIPTION      The class name of the PolicyAction subclass that is
                      instantiated.
     SYNTAX           string [MaxLen 256]
     QUALIFIER        key
 
     NAME             PolicyActionName
     DESCRIPTION      The identifying name of this policy action.
     SYNTAX           string [MaxLen 256]
     QUALIFIER        key
 
 
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 14.4. Naming Instances of PolicyRepository
 
   An instance of PolicyRepository is named by the two key properties
   CreationClassName and Name that it inherits from its superclass
   AdminDomain.  These properties are actually defined in  AdminDomain's
   superclass, System, and then inherited by AdminDomain.
 
   For instances of PolicyRepository itself, the value of
   CreationClassName must be "CIM_PolicyRepository".  (Recall that for
   readability the prefix "CIM_" has been omitted from all class names in
   this document).  If a subclass of PolicyRepository (perhaps
   QosPolicyRepository) is defined and instantiated, then the class name
   "CIM_QosPolicyRepository" is used in CreationClassName.
 
   The Name property simply completes the identification of the instance
   of PolicyRepository.
 
 14.5. Role of the CreationClassName Property in Naming
 
   To provide for more flexibility in instance naming, CIM makes use of a
   property called CreationClassName.  The idea of CreationClassName is
   to provide another dimension that can be used to avoid naming
   collisions, in the specific case of instances belonging to two
   different subclasses of a common  superclass.  An example will
   illustrate how CreationClassName works.
 
   Suppose we have instances of two different subclasses of
   PolicyCondition, FrameRelayPolicyCondition and BgpPolicyCondition, and
   that these instances apply to the same context.  If we had only the
   single key property PolicyConditionName available for distinguishing
   the two instances, then a collision would result from naming both of
   the instances with the key value PCName = "PC-1".  Thus policy
   administrators from widely different disciplines would have to
   coordinate their naming of PolicyConditions for this context.
 
   With CreationClassName, collisions of this type can be eliminated,
   without requiring coordination among the policy administrators.  The
   two instances can be distinguished by giving their CreationClassNames
   different values.  One instance is now identified with the two keys
 
   CreationClassName = "FrameRelayPolicyCondition" + PCName = "PC-1",
 
   while the other is identified with
 
   CreationClassName = "BgpPolicyCondition" + PCName = "PC-1".
 
   Each of the instantiable classes in the Core Model includes the
   CreationClassName property as a key in addition to its own class-
   specific key property.
 
 
 
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 Internet Draft       Policy Core Information Model            July 2000
 
 
 14.6. Object References
 
   Today, all CIM associations involve two object references.  CIM
   decomposes an object reference into two parts:  a high-order part that
   identifies an object manager and namespace, and a model path that
   identifies an object instance within a namespace.  The model path, in
   turn, can be decomposed into an object class identifier and a set of
   key values needed to identify an instance of that class.
 
   Because the object class identifier is part of the model path, a CIM
   object reference is strongly typed.  The GroupComponent object
   reference in the PolicyGroupInPolicyGroup association, for example,
   can only point to an instance of PolicyGroup, or to an instance of a
   subclass of PolicyGroup.  Contrast this with LDAP, where a DN pointer
   is completely untyped:  it identifies (by DN) an entry, but places no
   restriction on that entry's object class(es).
 
   An important difference between CIM property definitions and LDAP
   attribute type definitions was identified earlier in Section 6:  while
   an LDAP attribute type definition has global scope, a CIM property
   definition applies only to the class in which it is defined.  Thus
   properties having the same name in two different classes are free to
   have different data types.  CIM takes advantage of this flexibility by
   allowing the data type of an object reference to be overridden in a
   subclass of the association class in which it was initially defined.
 
   For example, the object reference GroupComponent is defined in the
   abstract aggregation class PolicyComponent to be a reference to an
   instance of the class Policy.  This data type for GroupComponent is
   then overridden in subclasses of PolicyComponent.  In
   PolicyGroupInPolicyGroup, for example, GroupComponent becomes a
   reference to an instance of PolicyGroup.  But in
   PolicyConditionInPolicyRule it becomes a reference to an instance of
   PolicyRule.  Of course there is not total freedom in this overriding
   of object references.  In order to remain consistent with its abstract
   superclass, a subclass of PolicyComponent can only override
   GroupComponent to be a reference to a subclass of Policy.  A Policy
   class is the generic context for the GroupComponent reference  in
   PolicyComponent.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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