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Versions: 00 01 02 03 04 05 rfc7408                      Standards Track
Internet Engineering Task Force                            E. Haleplidis
Internet-Draft                                      University of Patras
Updates: 5812 (if approved)                              August 21, 2014
Intended status: Standards Track
Expires: February 22, 2015


                         ForCES Model Extension
                  draft-ietf-forces-model-extension-04

Abstract

   Forwarding and Control Element Separation (ForCES) defines an
   architectural framework and associated protocols to standardize
   information exchange between the control plane and the forwarding
   plane in a ForCES Network Element (ForCES NE).  RFC5812 has defined
   the ForCES Model that provides a formal way to represent the
   capabilities, state, and configuration of forwarding elements within
   the context of the ForCES protocol, so that control elements (CEs)
   can control the FEs accordingly.  More specifically, the model
   describes the logical functions that are present in a forwarding
   element (FE), what capabilities these functions support, and how
   these functions are or can be interconnected.

   RFC5812 has been around for two years and experience in its use has
   shown room for small extensions without a need to alter the protocol
   while retaining backward compatibility with older xml libraries.
   This document updates RFC5812 and extends the model to allow complex
   datatypes for metadata, optional default values for datatypes,
   optional access types for structures and fixes an issue with Logical
   Functional Block (LFB) inheritance.  The document also introduces two
   new features a new event condition BecomesEqualTo and LFB properties.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."




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   This Internet-Draft will expire on February 22, 2015.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     1.2.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  ForCES Model Extensions . . . . . . . . . . . . . . . . . . .   4
     2.1.  Complex datatypes for Metadata  . . . . . . . . . . . . .   4
     2.2.  Optional Default Value for Datatypes  . . . . . . . . . .   5
     2.3.  Optional Access Type for Structs  . . . . . . . . . . . .   8
     2.4.  New Event Condition: BecomesEqualTo . . . . . . . . . . .  11
     2.5.  LFB Properties  . . . . . . . . . . . . . . . . . . . . .  12
     2.6.  LFB class inheritance . . . . . . . . . . . . . . . . . .  14
     2.7.  Enhancing XML Validation  . . . . . . . . . . . . . . . .  15
   3.  XML Extension Schema for LFB Class Library Documents  . . . .  15
   4.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  29
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  29
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  29
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  29
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  29
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  30
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  30

1.  Introduction

   The ForCES Model [RFC5812] presents a formal way to define Forwarding
   Elements (FE) Logical Function Blocks (LFBs) using the eXtensible
   Markup Language (XML).  [RFC5812] has been published a more than two
   years and current experience in its use has demonstrated need for
   adding new and changing existing modeling concepts.





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   Specifically this document updates the ForCES Model [RFC5812] to
   allow complex datatypes for metadata (Section 2.1), optional default
   values for datatypes (Section 2.2), optional access types for
   structures (Section 2.3) and fixes an issue with LFB class
   inheritance (Section 2.6).  Additionally the document introduces two
   new features, a new event condition BecomesEqualTo (Section 2.4) and
   LFB properties (Section 2.5).

   These extensions are an update to the ForCES model [RFC5812] and do
   not require any changes on the ForCES protocol [RFC5810] as they are
   simply changes of the schema definition.  Additionally backward
   compatibility is ensured as XML libraries produced with the earlier
   schema are still valid with the new one.  In order for XML libraries
   produced by the new schema to be compatible with existing ForCES
   implementations, the XML Libraries MUST NOT include any of the
   features described in this document, else the old implementation will
   be unable to parse the XML library.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

1.2.  Definitions

   This document uses the terminology defined in the ForCES Model in
   [RFC5812].  In particular, the reader is expected to be familiar with
   the following terms:

      FE Model

      LFB (Logical Functional Block) Class (or type)

      LFB Instance

      LFB Model

      Element

      Attribute

      LFB Metadata

      ForCES Component

      LFB Class Library




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2.  ForCES Model Extensions

2.1.  Complex datatypes for Metadata

   Section 4.6.  (Element for Metadata Definitions) in the ForCES Model
   [RFC5812] limits the datatype use in metadata to only atomic types.
   Figure 1 shows the xml schema excerpt where ony typeRef and atomic
   are allowed for a metadata definition.

       <xsd:complexType name="metadataDefsType">
         <xsd:sequence>
           <xsd:element name="metadataDef" maxOccurs="unbounded">
             <xsd:complexType>
               <xsd:sequence>
                 <xsd:element name="name" type="xsd:NMTOKEN"/>
                 <xsd:element ref="synopsis"/>
                 <xsd:element name="metadataID" type="xsd:integer"/>
                 <xsd:element ref="description" minOccurs="0"/>
                 <xsd:choice>
                   <xsd:element name="typeRef" type="typeRefNMTOKEN"/>
                   <xsd:element name="atomic" type="atomicType"/>
                 </xsd:choice>
               </xsd:sequence>
             </xsd:complexType>
           </xsd:element>
         </xsd:sequence>
       </xsd:complexType>

        Figure 1: Initial MetadataDefType Definition in the schema

   However there are cases where complex metadata are used in the
   datapath, for example two simple use cases can be seen in the
   OpenFlow 1.1 specification [OpenFlowSpec1.1] and beyond:

   1.  The Action Set metadata is an array of actions descriptors, which
       traverses the processing pipeline along with the packet data.

   2.  When a packet is received from a controller it may be accompanied
       by a list of actions, as metadata, to be performed on it prior to
       being sent on the processing pipeline.  This list of actions is
       also an array.

   With this extension (Figure 2), complex data types are also allowed,
   specifically structs and arrays as metadata.  The key declarations
   are required to check for validity of content keys in arrays and
   componentIDs in structs.





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         <xsd:complexType name="metadataDefsType">
         <xsd:sequence>
           <xsd:element name="metadataDef" maxOccurs="unbounded">
             <xsd:complexType>
               <xsd:sequence>
                 <xsd:element name="name" type="xsd:NMTOKEN"/>
                 <xsd:element ref="synopsis"/>
                 <xsd:element name="metadataID" type="xsd:integer"/>
                 <xsd:element ref="description" minOccurs="0"/>
                 <xsd:choice>
                   <xsd:element name="typeRef" type="typeRefNMTOKEN"/>
                   <xsd:element name="atomic" type="atomicType"/>
                   <xsd:element name="array" type="arrayType">
                     <xsd:key name="contentKeyID1">
                       <xsd:selector xpath="lfb:contentKey"/>
                       <xsd:field xpath="@contentKeyID"/>
                     </xsd:key>
                   </xsd:element>
                   <xsd:element name="struct" type="structType">
                     <xsd:key name="structComponentID1">
                       <xsd:selector xpath="lfb:component"/>
                       <xsd:field xpath="@componentID"/>
                     </xsd:key>
                   </xsd:element>
                 </xsd:choice>
               </xsd:sequence>
             </xsd:complexType>
           </xsd:element>
         </xsd:sequence>
       </xsd:complexType>

          Figure 2: New MetadataDefType Definition for the schema

2.2.  Optional Default Value for Datatypes

   In the original schema, default values can only be defined for
   datatypes defined inside LFB components and not inside structures or
   arrays.  Therefore default values of datatypes that are constantly
   being reused, e.g. counters with default value of 0, have to be
   constantly respecified.  Additionally, datatypes inside complex
   datatypes cannot be defined with a default value, e.g. a counter
   inside a struct that has a default value of 0.

   This extension allows the option to add default values to atomic and
   typeref types, whether they are as simple or complex datatypes.  A
   simple use case would be to have a struct component where one of the
   components is a counter which the default value would be zero.




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   This extension alters the definition of the typeDeclarationGroup in
   the XML schema from Figure 3 to Figure 4 to allow default values to
   TypeRef.

             <xsd:element name="typeRef" type="typeRefNMTOKEN"/>

    Figure 3: Initial Excerpt of typeDeclarationGroup Definition in the
                                  schema

                 <xsd:sequence>
             <xsd:element name="typeRef" type="typeRefNMTOKEN"/>
               <xsd:element name="DefaultValue" type="xsd:token"
                     minOccurs="0"/>
                 </xsd:sequence>

      Figure 4: New Excerpt of typeDeclarationGroup Definition in the
                                  schema

   Additionally this document appends to the initial declaration of the
   AtomicType, Figure 5, an optional defaultValue, Figure 6, to allow
   default values to Atomic datatypes.  Note that both declarations
   include the new special value validation described in Section 2.7

    <xsd:complexType name="atomicType">
      <xsd:sequence>
        <xsd:element name="baseType" type="typeRefNMTOKEN"/>
        <xsd:element name="rangeRestriction" type="rangeRestrictionType"
         minOccurs="0"/>
        <xsd:element name="specialValues" type="specialValuesType"
         minOccurs="0">
          <!-- Extension -->
          <xsd:key name="SpecialValue">
            <xsd:selector xpath="specialValue"/>
            <xsd:field xpath="@value"/>
          </xsd:key>
          <!-- /Extension -->
        </xsd:element>
      </xsd:sequence>

     Figure 5: Initial Excerpt of AtomicType Definition in the schema











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    <xsd:complexType name="atomicType">
      <xsd:sequence>
        <xsd:element name="baseType" type="typeRefNMTOKEN"/>
        <xsd:element name="rangeRestriction" type="rangeRestrictionType"
         minOccurs="0"/>
        <xsd:element name="specialValues" type="specialValuesType"
         minOccurs="0">
          <!-- Extension -->
          <xsd:key name="SpecialValue">
            <xsd:selector xpath="specialValue"/>
            <xsd:field xpath="@value"/>
          </xsd:key>
          <!-- /Extension -->
        </xsd:element>
        <!-- Extension -->
        <xsd:element name="defaultValue" type="xsd:token"
          minOccurs="0"/>
        <!-- /Extension -->
      </xsd:sequence>

       Figure 6: New Excerpt of AtomicType Definition in the schema

   Examples of using default values is depicted in Figure 7.

            <dataTypeDef>
              <name>Counter Values</name>
              <synopsis>Example default values in struct</synopsis>
              <struct>
                <component componentID="1">
                  <name>GoodPacketCoutner</name>
                  <synopsis>A counter for good packets</synopsis>
                  <typeRef>uint32</typeRef>
                  <DefaultValue>0</DefaultValue>
                </component>
                <component componentID="2">
                  <name>BadPacketCoutner</name>
                  <synopsis>A counter for bad packets</synopsis>
                  <typeRef>uint32</typeRef>
                  <DefaultValue>0</DefaultValue>
                </component>
              </struct>
            </dataTypeDef>

               Figure 7: Example of optional default values







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2.3.  Optional Access Type for Structs

   In the original schema, the access type can only be defined on
   components of an LFB and not on components within structs or arrays.
   That means that when it is a struct datatype it is not possible to
   fine-tune access type per component within the struct.  A simple use
   case would be to have a read-write struct component where one of the
   components is a counter where the access-type could be read-reset or
   read-only, e.g. a read-reset or a read-only counter inside a struct.

   This extension allows the definition of the access type for a struct
   component either in the datatype definitions or in the LFB component
   definitions.

   When optional access type for components within a struct are defined,
   these components's access type MUST override the access type of the
   struct.  For example if a struct has an access type of read-write but
   has a component that is a read-only counter, the counter's access
   type MUST be read-only.

   The access type for a component in a capability is always read-only
   per [RFC5812].  If an access type is provided for a component in a
   capability, the access type MUST be ignored.  Similarly if an access
   type is provided for a struct in a metadata the access type MUST be
   ignored.

   This extension alters the definition of the struct in the xml schema
   from Figure 8 to Figure 9.























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       <xsd:complexType name="structType">
        <xsd:sequence>
          <xsd:element name="derivedFrom" type="typeRefNMTOKEN"
            minOccurs="0"/>
          <xsd:element name="component" maxOccurs="unbounded">
            <xsd:complexType>
              <xsd:sequence>
                <xsd:element name="name" type="xsd:NMTOKEN"/>
                <xsd:element ref="synopsis"/>
                <xsd:element ref="description" minOccurs="0"/>
                <xsd:element name="optional" minOccurs="0"/>
                <xsd:group ref="typeDeclarationGroup"/>
              </xsd:sequence>
              <xsd:attribute name="componentID" type="xsd:unsignedInt"
               use="required"/>
            </xsd:complexType>
          </xsd:element>
        </xsd:sequence>
      </xsd:complexType>

       Figure 8: Initial xml for the struct definition in the schema






























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       <xsd:complexType name="structType">
        <xsd:sequence>
          <xsd:element name="derivedFrom" type="typeRefNMTOKEN"
            minOccurs="0"/>
          <xsd:element name="component" maxOccurs="unbounded">
            <xsd:complexType>
              <xsd:sequence>
                <xsd:element name="name" type="xsd:NMTOKEN"/>
                <xsd:element ref="synopsis"/>
                <xsd:element ref="description" minOccurs="0"/>
                <xsd:element name="optional" minOccurs="0"/>
                <xsd:group ref="typeDeclarationGroup"/>
              </xsd:sequence>
              <xsd:attribute name="access" use="optional"
                default="read-write">
                <xsd:simpleType>
                  <xsd:list itemType="accessModeType"/>
                </xsd:simpleType>
              </xsd:attribute>
              <xsd:attribute name="componentID" type="xsd:unsignedInt"
                use="required"/>
            </xsd:complexType>
          </xsd:element>
        </xsd:sequence>
      </xsd:complexType>

         Figure 9: New xml for the struct definition in the schema

   An example of using optional access types for structs can be depicted
   in Figure 10





















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            <component componentID="1" access="read-write">
               <name>PacketFlows</name>
               <synopsis>Packet Flows, match and counter</synopsis>
               <struct>
                <component componentID="1">
                  <name>FlowMatch</name>
                  <synopsis>Flow Match</synopsis>
                  <typeRef>MatchType</typeRef>
                </component>
                <component componentID="2" access="read-only">
                  <name>MatchCounter</name>
                  <synopsis>Packets matching the flow match</synopsis>
                  <typeRef>uint32</typeRef>
                  <DefaultValue>0</DefaultValue>
                </component>
              </struct>
            </component>

          Figure 10: Example of optional access types for struct

2.4.  New Event Condition: BecomesEqualTo

   This extensions adds one more event condition in the model schema,
   that of BecomesEqualTo.  The difference between Greater Than and Less
   Than, is that when the value becomes exactly that of the
   BecomesEqualTo, the event is triggered.  This event condition is
   particularly useful when there is a need to monitor one or more
   states of an LFB or the FE.  For example in the CE High Availability
   (CEHA) [RFC7121] RFC it may be useful for the master CE to know which
   backup CEs have just become associated in order to connect to them
   and begin synchronizing the state of the FE.  The master CE could
   always poll for such information but getting such an event will speed
   up the process and the event may be useful in other cases as well for
   monitoring state.

   The event MUST be triggered only when the value of the targeted
   component becomes equal to the event condition value.
   Implementations MUST NOT generate subsequent events while the
   targeted component's value remains equal to the event condition's
   value.

   The BecomesEqualTo is appended to the schema as follows:

                       <xsd:element name="eventBecomesEqualTo"
                  substitutionGroup="eventCondition"/>

    Figure 11: New Excerpt of BecomesEqualTo event condition definition
                               in the schema



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   It can become useful for the CE to be notified when the state has
   changed once the BecomesEqualTo event has been triggered, e.g. the CE
   may need to know when a backup CE has lost association.  Such an
   event can be generated either by defining a second event on the same
   component, namely an Event Changed, or by simply reusing
   BecomesEqualTo and use event properties, in particular event
   hysteresis.  We append the following definition for the event
   hysteresis defined in section 4.8.5.2 in [RFC5812], with V being the
   hysteresis value:

   o  For an <eventBecomesEqualTo/> condition, after the last
      notification a new <eventBecomesEqualTo/> notification MUST be
      generated only one time once the value has changed by +/- V.

   For example using the value of 1 for V, will in effect create a
   singular event that will notify the CE that the value has changed by
   at least 1.

   A developer of a CE should consider using count or time filtering to
   avoid being overrun by messages, e.g. in the case of rapid state
   changes.

2.5.  LFB Properties

   The previous model definition specifies properties for components of
   LFBs.  Experience has shown that, at least for debug reasons, it
   would be useful to have statistics per LFB instance to monitor sent
   and received messages and errors in communication between CE and FE.
   These properties are read-only.

   In order to avoid ambiguity on protocol path semantics, this document
   specifies that the LFB component with ID 0 specifically MUST refer to
   LFB properties and ID 0 MUST NOT be used for any component
   definition.  This disallowment is backwards compatible as no known
   LFB definition uses LFB component with ID 0.  Any command with a path
   starting from LFB component 0 refers to LFB properties.  The
   following change in the xml schema disallows usage of LFB component
   0:

              <xsd:attribute name="componentID" type="xsd:unsignedInt"
               use="required">

               Figure 12: Initial xml for LFB Component IDs








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                <!-- Extension Added restriction to component ID -->
                <xsd:attribute name="componentID" use="required">
                  <xsd:simpleType>
                    <xsd:restriction base="xsd:unsignedInt">
                      <xsd:minExclusive value="0"/>
                    </xsd:restriction>
                  </xsd:simpleType>
                </xsd:attribute>
                <!-- End of extension -->

        Figure 13: New xml to disallow usage of 0 as LFB Component

   The following datatype definitions are to be used as properties for
   LFB instances.

         <dataTypeDef>
            <name>LFBProperties</name>
            <synopsis>LFB Properties definition</synopsis>
            <struct>
               <component componentID="1">
                  <name>PacketsSentToCE</name>
                  <synopsis>Packets sent to CE</synopsis>
                  <typeRef>uint32</typeRef>
               </component>
               <component componentID="2">
                  <name>SentErrorPacketsToCE</name>
                  <synopsis>Error Packets sent to CE</synopsis>
                  <typeRef>uint32</typeRef>
               </component>
               <component componentID="3">
                  <name>BytesSentToCE</name>
                  <synopsis>Bytes sent to CE</synopsis>
                  <typeRef>uint32</typeRef>
               </component>
               <component componentID="4">
                  <name>SentErrorBytesToCE</name>
                  <synopsis>Error Bytes sent to CE</synopsis>
                  <typeRef>uint32</typeRef>
               </component>
               <component componentID="5">
                  <name>PacketsReceivedFromCE</name>
                  <synopsis>Packets received from CE</synopsis>
                  <typeRef>uint32</typeRef>
               </component>
               <component componentID="6">
                  <name>ReceivedErrorPacketsFromCE</name>
                  <synopsis>Error Packets received from CE</synopsis>
                  <typeRef>uint32</typeRef>



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               </component>
               <component componentID="7">
                  <name>BytesReceivedFromCE</name>
                  <synopsis>Bytesreceived from CE</synopsis>
                  <typeRef>uint32</typeRef>
               </component>
               <component componentID="8">
                  <name>ReceivedErrorBytesFromCE</name>
                  <synopsis>Error Bytes received from CE</synopsis>
                  <typeRef>uint32</typeRef>
               </component>
            </struct>
         </dataTypeDef>


                       Properties for LFB instances

2.6.  LFB class inheritance

   The ForCES model [RFC5812] allows inheritance for LFB classes.
   However the xml schema defines only the LFB class from which an LFB
   class inherits.  Recent implementations have identified an issue
   where ambiguity rises when different versions of the parent LFB class
   exists.  This document augments the derivedFrom part of the LFB class
   definition with an optional version attribute when the derivedFrom
   field is used.

   Having the version attribute as optional was a decision based on the
   need to maintain backwards compatibility with the XML schema defined
   in [RFC5812].  However if the version is omitted then the derivedFrom
   will always specify the first version of the parent LFB class, which
   usually is version 1.0.

   This extension alters the definition of the derivedFrom in the xml
   schema from Figure 14 to Figure 15.

                       <xsd:element name="derivedFrom" minOccurs="0"/>

           Figure 14: Initial xml for the LFB class inheritance












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                       <xsd:element name="derivedFrom" minOccurs="0">
                         <xsd:complexType>
                           <xsd:simpleContent>
                             <xsd:extension base="xsd:NMTOKEN">
                               <xsd:attribute name="version"
                                 type="versionType" use="optional"/>
                             </xsd:extension>
                           </xsd:simpleContent>
                         </xsd:complexType>
                       </xsd:element>

             Figure 15: New xml for the LFB class inheritance

   An example of the use of the version attribute is given in Figure 16

                <derivedFrom version="1.0">EtherPHYCop</derivedFrom>

      Figure 16: Example of use of new xml for LFB class Inheritance

2.7.  Enhancing XML Validation

   As specified earlier this is not an extension but an enhancement of
   the schema to provide additional validation rules.  This includes
   adding new key declarations to provide uniqueness as defined by the
   ForCES Model [RFC5812].  Such validations work only on within the
   same xml file.

   This document introduces the following validation rules that did not
   exist in the original schema in [RFC5812]:

   1.  Each metadata ID must be unique.

   2.  LFB Class IDs must be unique.

   3.  Component ID, Capability ID and Event Base ID must be unique per
       LFB.

   4.  Event IDs must be unique per LFB.

   5.  Special Values in Atomic datatypes must be unique per atomic
       datatype.

3.  XML Extension Schema for LFB Class Library Documents

   This section includes the new XML Schema.  Note that the namespace
   number has been updated from 1.0 to 1.1

<?xml version="1.0" encoding="UTF-8"?>



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<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
   xmlns="urn:ietf:params:xml:ns:forces:lfbmodel:1.1"
   xmlns:lfb="urn:ietf:params:xml:ns:forces:lfbmodel:1.1"
   targetNamespace="urn:ietf:params:xml:ns:forces:lfbmodel:1.1"
   elementFormDefault="qualified" attributeFormDefault="unqualified">
   <xsd:annotation>
      <xsd:documentation xml:lang="en">
         Schema for Defining LFB Classes and associated types
         (frames, data types for LFB attributes, and metadata).
      </xsd:documentation>
   </xsd:annotation>
   <xsd:element name="description" type="xsd:string"/>
   <xsd:element name="synopsis" type="xsd:string"/>
   <!-- Document root element: LFBLibrary -->
   <xsd:element name="LFBLibrary">
      <xsd:complexType>
         <xsd:sequence>
            <xsd:element ref="description" minOccurs="0"/>
            <xsd:element name="load" type="loadType"
               minOccurs="0" maxOccurs="unbounded"/>
            <xsd:element name="frameDefs" type="frameDefsType"
               minOccurs="0"/>
            <xsd:element name="dataTypeDefs" type="dataTypeDefsType"
               minOccurs="0"/>
            <xsd:element name="metadataDefs" type="metadataDefsType"
               minOccurs="0"/>
            <xsd:element name="LFBClassDefs" type="LFBClassDefsType"
               minOccurs="0"/>
         </xsd:sequence>
         <xsd:attribute name="provides" type="xsd:Name"
            use="required"/>
      </xsd:complexType>
      <!-- Uniqueness constraints -->
      <xsd:key name="frame">
         <xsd:selector xpath="lfb:frameDefs/lfb:frameDef"/>
         <xsd:field xpath="lfb:name"/>
      </xsd:key>
      <xsd:key name="dataType">
         <xsd:selector xpath="lfb:dataTypeDefs/lfb:dataTypeDef"/>
         <xsd:field xpath="lfb:name"/>
      </xsd:key>
      <xsd:key name="metadataDef">
         <xsd:selector xpath="lfb:metadataDefs/lfb:metadataDef"/>
         <xsd:field xpath="lfb:name"/>
      </xsd:key>
      <xsd:key name="metadataDefID">
         <xsd:selector xpath="lfb:metadataDefs/lfb:metadataDef"/>
         <xsd:field xpath="lfb:metadataID"/>



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      </xsd:key>
      <xsd:key name="LFBClassDef">
         <xsd:selector xpath="lfb:LFBClassDefs/lfb:LFBClassDef"/>
         <xsd:field xpath="lfb:name"/>
      </xsd:key>
      <xsd:key name="LFBClassDefID">
         <xsd:selector xpath="lfb:LFBClassDefs/lfb:LFBClassDef"/>
         <xsd:field xpath="@LFBClassID"/>
      </xsd:key>
   </xsd:element>
   <xsd:complexType name="loadType">
      <xsd:attribute name="library" type="xsd:Name" use="required"/>
      <xsd:attribute name="location" type="xsd:anyURI"
         use="optional"/>
   </xsd:complexType>
   <xsd:complexType name="frameDefsType">
      <xsd:sequence>
         <xsd:element name="frameDef" maxOccurs="unbounded">
            <xsd:complexType>
               <xsd:sequence>
                  <xsd:element name="name" type="xsd:NMTOKEN"/>
                  <xsd:element ref="synopsis"/>
                  <xsd:element ref="description"
                     minOccurs="0"/>
               </xsd:sequence>
            </xsd:complexType>
         </xsd:element>
      </xsd:sequence>
   </xsd:complexType>
   <xsd:complexType name="dataTypeDefsType">
      <xsd:sequence>
         <xsd:element name="dataTypeDef" maxOccurs="unbounded">
            <xsd:complexType>
               <xsd:sequence>
                  <xsd:element name="name" type="xsd:NMTOKEN"/>
                  <xsd:element name="derivedFrom" type="xsd:NMTOKEN"
                     minOccurs="0"/>
                  <xsd:element ref="synopsis"/>
                  <xsd:element ref="description"
                     minOccurs="0"/>
                  <xsd:group ref="typeDeclarationGroup"/>
               </xsd:sequence>
            </xsd:complexType>
         </xsd:element>
      </xsd:sequence>
   </xsd:complexType>
   <!-- Predefined (built-in) atomic data-types are: char, uchar,
   int16, uint16, int32, uint32, int64, uint64, string[N], string,



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   byte[N], boolean, octetstring[N], float32, float64 -->
   <xsd:group name="typeDeclarationGroup">
      <xsd:choice>
         <!-- Extension -->
         <xsd:sequence>
            <!-- /Extension -->
            <xsd:element name="typeRef" type="typeRefNMTOKEN"/>
            <!-- Extension -->
            <xsd:element name="DefaultValue" type="xsd:token"
               minOccurs="0"/>
         </xsd:sequence>
         <!-- /Extension -->
         <xsd:element name="atomic" type="atomicType"/>
         <xsd:element name="array" type="arrayType">
            <!-- Extension -->
            <!--declare keys to have unique IDs -->
            <xsd:key name="contentKeyID">
               <xsd:selector xpath="lfb:contentKey"/>
               <xsd:field xpath="@contentKeyID"/>
            </xsd:key>
            <!-- /Extension -->
         </xsd:element>
         <xsd:element name="struct" type="structType">
            <!-- Extension -->
            <!-- key declaration to make componentIDs
              unique in a struct -->
            <xsd:key name="structComponentID">
               <xsd:selector xpath="lfb:component"/>
               <xsd:field xpath="@componentID"/>
            </xsd:key>
            <!-- /Extension -->
         </xsd:element>
         <xsd:element name="union" type="structType"/>
         <xsd:element name="alias" type="typeRefNMTOKEN"/>
      </xsd:choice>
   </xsd:group>
   <xsd:simpleType name="typeRefNMTOKEN">
      <xsd:restriction base="xsd:token">
         <xsd:pattern value="\c+"/>
         <xsd:pattern value="string\[\d+\]"/>
         <xsd:pattern value="byte\[\d+\]"/>
         <xsd:pattern value="octetstring\[\d+\]"/>
      </xsd:restriction>
   </xsd:simpleType>
   <xsd:complexType name="atomicType">
      <xsd:sequence>
         <xsd:element name="baseType" type="typeRefNMTOKEN"/>
         <xsd:element name="rangeRestriction"



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           type="rangeRestrictionType" minOccurs="0"/>
         <xsd:element name="specialValues" type="specialValuesType"
            minOccurs="0">
            <!-- Extension -->
            <xsd:key name="SpecialValue">
               <xsd:selector xpath="specialValue"/>
               <xsd:field xpath="@value"/>
            </xsd:key>
            <!-- /Extension -->
         </xsd:element>
         <!-- Extension -->
         <xsd:element name="defaultValue" type="xsd:token"
            minOccurs="0"/>
         <!-- /Extension -->
      </xsd:sequence>
   </xsd:complexType>
   <xsd:complexType name="rangeRestrictionType">
      <xsd:sequence>
         <xsd:element name="allowedRange" maxOccurs="unbounded">
            <xsd:complexType>
               <xsd:attribute name="min" type="xsd:integer"
                  use="required"/>
               <xsd:attribute name="max" type="xsd:integer"
                  use="required"/>
            </xsd:complexType>
         </xsd:element>
      </xsd:sequence>
   </xsd:complexType>
   <xsd:complexType name="specialValuesType">
      <xsd:sequence>
         <xsd:element name="specialValue" maxOccurs="unbounded">
            <xsd:complexType>
               <xsd:sequence>
                  <xsd:element name="name" type="xsd:NMTOKEN"/>
                  <xsd:element ref="synopsis"/>
               </xsd:sequence>
               <xsd:attribute name="value" type="xsd:token"/>
            </xsd:complexType>
         </xsd:element>
      </xsd:sequence>
   </xsd:complexType>
   <xsd:complexType name="arrayType">
      <xsd:sequence>
         <xsd:group ref="typeDeclarationGroup"/>
         <xsd:element name="contentKey" minOccurs="0"
            maxOccurs="unbounded">
            <xsd:complexType>
               <xsd:sequence>



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                  <xsd:element name="contentKeyField"
                     type="xsd:string" maxOccurs="unbounded"/>
               </xsd:sequence>
               <xsd:attribute name="contentKeyID" type="xsd:integer"
                  use="required"/>
            </xsd:complexType>
         </xsd:element>
      </xsd:sequence>
      <xsd:attribute name="type" use="optional" default="variable-size">
         <xsd:simpleType>
            <xsd:restriction base="xsd:string">
               <xsd:enumeration value="fixed-size"/>
               <xsd:enumeration value="variable-size"/>
            </xsd:restriction>
         </xsd:simpleType>
      </xsd:attribute>
      <xsd:attribute name="length" type="xsd:integer"
         use="optional"/>
      <xsd:attribute name="maxLength" type="xsd:integer"
         use="optional"/>
   </xsd:complexType>
   <xsd:complexType name="structType">
      <xsd:sequence>
         <xsd:element name="derivedFrom" type="typeRefNMTOKEN"
            minOccurs="0"/>
         <xsd:element name="component" maxOccurs="unbounded">
            <xsd:complexType>
               <xsd:sequence>
                  <xsd:element name="name" type="xsd:NMTOKEN"/>
                  <xsd:element ref="synopsis"/>
                  <xsd:element ref="description"
                     minOccurs="0"/>
                  <xsd:element name="optional" minOccurs="0"/>
                  <xsd:group ref="typeDeclarationGroup"/>
               </xsd:sequence>
               <xsd:attribute name="access" use="optional"
                  default="read-write">
                  <xsd:simpleType>
                     <xsd:list itemType="accessModeType"/>
                  </xsd:simpleType>
               </xsd:attribute>
               <xsd:attribute name="componentID" type="xsd:unsignedInt"
                  use="required"/>
            </xsd:complexType>
         </xsd:element>
      </xsd:sequence>
   </xsd:complexType>
   <xsd:complexType name="metadataDefsType">



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      <xsd:sequence>
         <xsd:element name="metadataDef" maxOccurs="unbounded">
            <xsd:complexType>
               <xsd:sequence>
                  <xsd:element name="name" type="xsd:NMTOKEN"/>
                  <xsd:element ref="synopsis"/>
                  <xsd:element name="metadataID" type="xsd:integer"/>
                  <xsd:element ref="description"
                     minOccurs="0"/>
                  <xsd:choice>
                     <xsd:element name="typeRef" type="typeRefNMTOKEN"/>
                     <xsd:element name="atomic" type="atomicType"/>
                     <!-- Extension -->
                     <xsd:element name="array" type="arrayType">
                        <!--declare keys to have unique IDs -->
                        <xsd:key name="contentKeyID1">
                           <xsd:selector xpath="lfb:contentKey"/>
                           <xsd:field xpath="@contentKeyID"/>
                        </xsd:key>
                        <!-- /Extension -->
                     </xsd:element>
                     <xsd:element name="struct" type="structType">
                        <!-- Extension -->
                        <!-- key declaration to make componentIDs
                           unique in a struct -->
                        <xsd:key name="structComponentID1">
                           <xsd:selector xpath="lfb:component"/>
                           <xsd:field xpath="@componentID"/>
                        </xsd:key>
                        <!-- /Extension -->
                     </xsd:element>
                  </xsd:choice>
               </xsd:sequence>
            </xsd:complexType>
         </xsd:element>
      </xsd:sequence>
   </xsd:complexType>
   <xsd:complexType name="LFBClassDefsType">
      <xsd:sequence>
         <xsd:element name="LFBClassDef" maxOccurs="unbounded">
            <xsd:complexType>
               <xsd:sequence>
                  <xsd:element name="name" type="xsd:NMTOKEN"/>
                  <xsd:element ref="synopsis"/>
                  <xsd:element name="version" type="versionType"/>
                  <xsd:element name="derivedFrom" minOccurs="0">
                    <xsd:complexType>
                      <xsd:simpleContent>



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                        <xsd:extension base="xsd:NMTOKEN">
                          <xsd:attribute name="version"
                            type="versionType" use="optional"/>
                        </xsd:extension>
                      </xsd:simpleContent>
                    </xsd:complexType>
                  </xsd:element>
                  <xsd:element name="inputPorts"
                   type="inputPortsType" minOccurs="0"/>
                  <xsd:element name="outputPorts"
                   type="outputPortsType" minOccurs="0"/>
                  <xsd:element name="components"
                   type="LFBComponentsType" minOccurs="0"/>
                  <xsd:element name="capabilities"
                   type="LFBCapabilitiesType" minOccurs="0"/>
                  <xsd:element name="events" type="eventsType"
                     minOccurs="0"/>
                  <xsd:element ref="description"
                     minOccurs="0"/>
               </xsd:sequence>
               <xsd:attribute name="LFBClassID" type="xsd:unsignedInt"
                  use="required"/>
            </xsd:complexType>
            <!-- Key constraint to ensure unique attribute names
            within a class: -->
            <xsd:key name="components">
               <xsd:selector xpath="lfb:components/lfb:component"/>
               <xsd:field xpath="lfb:name"/>
            </xsd:key>
            <xsd:key name="capabilities">
               <xsd:selector xpath="lfb:capabilities/lfb:capability"/>
               <xsd:field xpath="lfb:name"/>
            </xsd:key>
            <xsd:key name="events">
               <xsd:selector xpath="lfb:events/lfb:event"/>
               <xsd:field xpath="lfb:name"/>
            </xsd:key>
            <xsd:key name="eventsIDs">
               <xsd:selector xpath="lfb:events/lfb:event"/>
               <xsd:field xpath="@eventID"/>
            </xsd:key>
            <xsd:key name="componentIDs">
               <xsd:selector xpath="lfb:components/lfb:component"/>
               <xsd:field xpath="@componentID"/>
            </xsd:key>
            <xsd:key name="capabilityIDs">
               <xsd:selector xpath="lfb:capabilities/lfb:capability"/>
               <xsd:field xpath="@componentID"/>



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            </xsd:key>
            <xsd:key name="ComponentCapabilityComponentIDUniqueness">
               <xsd:selector
                  xpath="lfb:components/lfb:component|
                  lfb:capabilities/lfb:capability|lfb:events"/>
               <xsd:field xpath="@componentID|@baseID"/>
            </xsd:key>
         </xsd:element>
      </xsd:sequence>
   </xsd:complexType>
   <xsd:simpleType name="versionType">
      <xsd:restriction base="xsd:NMTOKEN">
         <xsd:pattern value="[1-9][0-9]*\.([1-9][0-9]*|0)"/>
      </xsd:restriction>
   </xsd:simpleType>
   <xsd:complexType name="inputPortsType">
      <xsd:sequence>
         <xsd:element name="inputPort" type="inputPortType"
            maxOccurs="unbounded"/>
      </xsd:sequence>
   </xsd:complexType>
   <xsd:complexType name="inputPortType">
      <xsd:sequence>
         <xsd:element name="name" type="xsd:NMTOKEN"/>
         <xsd:element ref="synopsis"/>
         <xsd:element name="expectation" type="portExpectationType"/>
         <xsd:element ref="description" minOccurs="0"/>
      </xsd:sequence>
      <xsd:attribute name="group" type="xsd:boolean"
         use="optional" default="0"/>
   </xsd:complexType>
   <xsd:complexType name="portExpectationType">
      <xsd:sequence>
         <xsd:element name="frameExpected" minOccurs="0">
            <xsd:complexType>
               <xsd:sequence>
                  <!-- ref must refer to a name of a defined
                    frame type -->
                  <xsd:element name="ref" type="xsd:string"
                     maxOccurs="unbounded"/>
               </xsd:sequence>
            </xsd:complexType>
         </xsd:element>
         <xsd:element name="metadataExpected" minOccurs="0">
            <xsd:complexType>
               <xsd:choice maxOccurs="unbounded">
                  <!--ref must refer to a name of a defined metadata-->
                  <xsd:element name="ref" type="metadataInputRefType"/>



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                  <xsd:element name="one-of"
                     type="metadataInputChoiceType"/>
               </xsd:choice>
            </xsd:complexType>
         </xsd:element>
      </xsd:sequence>
   </xsd:complexType>
   <xsd:complexType name="metadataInputChoiceType">
      <xsd:choice minOccurs="2" maxOccurs="unbounded">
         <!-- ref must refer to a name of a defined metadata -->
         <xsd:element name="ref" type="xsd:NMTOKEN"/>
         <xsd:element name="one-of" type="metadataInputChoiceType"/>
         <xsd:element name="metadataSet" type="metadataInputSetType"/>
      </xsd:choice>
   </xsd:complexType>
   <xsd:complexType name="metadataInputSetType">
      <xsd:choice minOccurs="2" maxOccurs="unbounded">
         <!-- ref must refer to a name of a defined metadata -->
         <xsd:element name="ref" type="metadataInputRefType"/>
         <xsd:element name="one-of" type="metadataInputChoiceType"/>
      </xsd:choice>
   </xsd:complexType>
   <xsd:complexType name="metadataInputRefType">
      <xsd:simpleContent>
         <xsd:extension base="xsd:NMTOKEN">
            <xsd:attribute name="dependency" use="optional"
               default="required">
               <xsd:simpleType>
                  <xsd:restriction base="xsd:string">
                     <xsd:enumeration value="required"/>
                     <xsd:enumeration value="optional"/>
                  </xsd:restriction>
               </xsd:simpleType>
            </xsd:attribute>
            <xsd:attribute name="defaultValue" type="xsd:token"
               use="optional"/>
         </xsd:extension>
      </xsd:simpleContent>
   </xsd:complexType>
   <xsd:complexType name="outputPortsType">
      <xsd:sequence>
         <xsd:element name="outputPort" type="outputPortType"
            maxOccurs="unbounded"/>
      </xsd:sequence>
   </xsd:complexType>
   <xsd:complexType name="outputPortType">
      <xsd:sequence>
         <xsd:element name="name" type="xsd:NMTOKEN"/>



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         <xsd:element ref="synopsis"/>
         <xsd:element name="product" type="portProductType"/>
         <xsd:element ref="description" minOccurs="0"/>
      </xsd:sequence>
      <xsd:attribute name="group" type="xsd:boolean"
         use="optional" default="0"/>
   </xsd:complexType>
   <xsd:complexType name="portProductType">
      <xsd:sequence>
         <xsd:element name="frameProduced" minOccurs="0">
            <xsd:complexType>
               <xsd:sequence>
                  <!-- ref must refer to a name of a defined
                     frame type -->
                  <xsd:element name="ref" type="xsd:NMTOKEN"
                     maxOccurs="unbounded"/>
               </xsd:sequence>
            </xsd:complexType>
         </xsd:element>
         <xsd:element name="metadataProduced" minOccurs="0">
            <xsd:complexType>
               <xsd:choice maxOccurs="unbounded">
                  <!-- ref must refer to a name of a
                     defined metadata -->
                  <xsd:element name="ref"
                     type="metadataOutputRefType"/>
                  <xsd:element name="one-of"
                     type="metadataOutputChoiceType"/>
               </xsd:choice>
            </xsd:complexType>
         </xsd:element>
      </xsd:sequence>
   </xsd:complexType>
   <xsd:complexType name="metadataOutputChoiceType">
      <xsd:choice minOccurs="2" maxOccurs="unbounded">
         <!-- ref must refer to a name of a defined metadata -->
         <xsd:element name="ref" type="xsd:NMTOKEN"/>
         <xsd:element name="one-of" type="metadataOutputChoiceType"/>
         <xsd:element name="metadataSet" type="metadataOutputSetType"/>
      </xsd:choice>
   </xsd:complexType>
   <xsd:complexType name="metadataOutputSetType">
      <xsd:choice minOccurs="2" maxOccurs="unbounded">
         <!-- ref must refer to a name of a defined metadata -->
         <xsd:element name="ref" type="metadataOutputRefType"/>
         <xsd:element name="one-of" type="metadataOutputChoiceType"/>
      </xsd:choice>
   </xsd:complexType>



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   <xsd:complexType name="metadataOutputRefType">
      <xsd:simpleContent>
         <xsd:extension base="xsd:NMTOKEN">
            <xsd:attribute name="availability" use="optional"
               default="unconditional">
               <xsd:simpleType>
                  <xsd:restriction base="xsd:string">
                     <xsd:enumeration value="unconditional"/>
                     <xsd:enumeration value="conditional"/>
                  </xsd:restriction>
               </xsd:simpleType>
            </xsd:attribute>
         </xsd:extension>
      </xsd:simpleContent>
   </xsd:complexType>
   <xsd:complexType name="LFBComponentsType">
      <xsd:sequence>
         <xsd:element name="component" maxOccurs="unbounded">
            <xsd:complexType>
               <xsd:sequence>
                  <xsd:element name="name" type="xsd:NMTOKEN"/>
                  <xsd:element ref="synopsis"/>
                  <xsd:element ref="description"
                     minOccurs="0"/>
                  <xsd:element name="optional" minOccurs="0"/>
                  <xsd:group ref="typeDeclarationGroup"/>
                  <xsd:element name="defaultValue" type="xsd:token"
                     minOccurs="0"/>
               </xsd:sequence>
               <xsd:attribute name="access" use="optional"
                  default="read-write">
                  <xsd:simpleType>
                     <xsd:list itemType="accessModeType"/>
                  </xsd:simpleType>
               </xsd:attribute>
               <!-- Extension Added restriction to component ID -->
               <xsd:attribute name="componentID" use="required">
                  <xsd:simpleType>
                     <xsd:restriction base="xsd:unsignedInt">
                        <xsd:minExclusive value="0"/>
                     </xsd:restriction>
                  </xsd:simpleType>
               </xsd:attribute>
               <!-- End of extension -->
            </xsd:complexType>
         </xsd:element>
      </xsd:sequence>
   </xsd:complexType>



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   <xsd:simpleType name="accessModeType">
      <xsd:restriction base="xsd:NMTOKEN">
         <xsd:enumeration value="read-only"/>
         <xsd:enumeration value="read-write"/>
         <xsd:enumeration value="write-only"/>
         <xsd:enumeration value="read-reset"/>
         <xsd:enumeration value="trigger-only"/>
      </xsd:restriction>
   </xsd:simpleType>
   <xsd:complexType name="LFBCapabilitiesType">
      <xsd:sequence>
         <xsd:element name="capability" maxOccurs="unbounded">
            <xsd:complexType>
               <xsd:sequence>
                  <xsd:element name="name" type="xsd:NMTOKEN"/>
                  <xsd:element ref="synopsis"/>
                  <xsd:element ref="description"
                     minOccurs="0"/>
                  <xsd:element name="optional" minOccurs="0"/>
                  <xsd:group ref="typeDeclarationGroup"/>
               </xsd:sequence>
               <xsd:attribute name="componentID" type="xsd:integer"
                  use="required"/>
            </xsd:complexType>
         </xsd:element>
      </xsd:sequence>
   </xsd:complexType>
   <xsd:complexType name="eventsType">
      <xsd:sequence>
         <xsd:element name="event" maxOccurs="unbounded">
            <xsd:complexType>
               <xsd:sequence>
                  <xsd:element name="name" type="xsd:NMTOKEN"/>
                  <xsd:element ref="synopsis"/>
                  <xsd:element name="eventTarget"
                    type="eventPathType"/>
                  <xsd:element ref="eventCondition"/>
                  <xsd:element name="eventReports"
                   type="eventReportsType" minOccurs="0"/>
                  <xsd:element ref="description"
                     minOccurs="0"/>
               </xsd:sequence>
               <xsd:attribute name="eventID" type="xsd:integer"
                  use="required"/>
            </xsd:complexType>
         </xsd:element>
      </xsd:sequence>
      <xsd:attribute name="baseID" type="xsd:integer"



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         use="optional"/>
   </xsd:complexType>
   <!-- the substitution group for the event conditions -->
   <xsd:element name="eventCondition" abstract="true"/>
   <xsd:element name="eventCreated"
    substitutionGroup="eventCondition"/>
   <xsd:element name="eventDeleted"
    substitutionGroup="eventCondition"/>
   <xsd:element name="eventChanged"
    substitutionGroup="eventCondition"/>
   <xsd:element name="eventGreaterThan"
    substitutionGroup="eventCondition"/>
   <xsd:element name="eventLessThan"
    substitutionGroup="eventCondition"/>
   <!-- Extension -->
   <xsd:element name="eventBecomesEqualTo"
      substitutionGroup="eventCondition"/>
   <!-- /Extension -->
   <xsd:complexType name="eventPathType">
      <xsd:sequence>
         <xsd:element ref="eventPathPart" maxOccurs="unbounded"/>
      </xsd:sequence>
   </xsd:complexType>
   <!-- the substitution group for the event path parts -->
   <xsd:element name="eventPathPart" type="xsd:string"
      abstract="true"/>
   <xsd:element name="eventField" type="xsd:string"
      substitutionGroup="eventPathPart"/>
   <xsd:element name="eventSubscript" type="xsd:string"
      substitutionGroup="eventPathPart"/>
   <xsd:complexType name="eventReportsType">
      <xsd:sequence>
         <xsd:element name="eventReport" type="eventPathType"
            maxOccurs="unbounded"/>
      </xsd:sequence>
   </xsd:complexType>
   <xsd:simpleType name="booleanType">
      <xsd:restriction base="xsd:string">
         <xsd:enumeration value="0"/>
         <xsd:enumeration value="1"/>
      </xsd:restriction>
   </xsd:simpleType>
</xsd:schema>

                           ForCES LFB XML Schema






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4.  Acknowledgements

   The author would like to acknowledge Joel Halpern, Jamal Hadi Salim
   and Dave Hood for their comments and discussion that helped shape
   this document in a better way.  Adrian Farrel for his AD review and
   Ben Campbell for his Gen-ART review which both improved the quality
   of this document.

5.  IANA Considerations

   IANA has registered a new XML namespace, as per the guidelines in RFC
   3688 [RFC3688].

   URI: The URI for this namespace is

   urn:ietf:params:xml:ns:forces:lfbmodel:1.1

   Registrant Contact: IESG

   XML: none, this is an XML namespace

6.  Security Considerations

   This document adds only a few constructs to the initial model defined
   in [RFC5812], namely namely a new event, some new properties and a
   way to define optional access types and complex metadata.  In
   addition this document addresses and clarifies an issue with the
   inheritance model by introducing the version of the derivedFrom LFB
   class.  These constructs and the inheritance model change do not
   change the nature of the initial model.

   Thus the security considerations defined in [RFC5812] applies to this
   document as well as the changes proposed here are simply constructs
   to write XML library definitions, as where in [RFC5812] and clarifies
   the inheritance issue of the initial model and both have no effect on
   security semantics with the protocol.

7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              January 2004.





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Internet-Draft           ForCES Model Extension              August 2014


   [RFC5810]  Doria, A., Hadi Salim, J., Haas, R., Khosravi, H., Wang,
              W., Dong, L., Gopal, R., and J. Halpern, "Forwarding and
              Control Element Separation (ForCES) Protocol
              Specification", RFC 5810, March 2010.

   [RFC5812]  Halpern, J. and J. Hadi Salim, "Forwarding and Control
              Element Separation (ForCES) Forwarding Element Model", RFC
              5812, March 2010.

   [RFC7121]  Ogawa, K., Wang, W., Haleplidis, E., and J. Hadi Salim,
              "High Availability within a Forwarding and Control Element
              Separation (ForCES) Network Element", RFC 7121, February
              2014.

7.2.  Informative References

   [OpenFlowSpec1.1]
              http://www.OpenFlow.org/, "The OpenFlow 1.1
              Specification.", <http://www.OpenFlow.org/documents/
              OpenFlow-spec-v1.1.0.pdf>.

Author's Address

   Evangelos Haleplidis
   University of Patras
   Department of Electrical and Computer Engineering
   Patras  26500
   Greece

   Email: ehalep@ece.upatras.gr





















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