ForCES Model Extension
draft-ietf-forces-model-extension-02

Internet Engineering Task Force                            E. Haleplidis
Internet-Draft                                      University of Patras
Intended status: Standards Track                            May 20, 2014
Expires: November 21, 2014

                         ForCES Model Extension
                  draft-ietf-forces-model-extension-02

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 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 an 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 extends the model to allow complex datatypes for
   metadata, optional default values for datatypes, optional access
   types for structures and fixes an issue with 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
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 21, 2014.

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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
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   described in the Simplified BSD License.

Table of Contents

   1.  Terminology and Conventions . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   2
     1.2.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  ForCES Model Extension proposal . . . . . . . . . . . . . . .   4
     3.1.  Complex datatypes for Metadata  . . . . . . . . . . . . .   4
     3.2.  Optional Default Value for Datatypes  . . . . . . . . . .   6
     3.3.  Optional Access Type for Structs  . . . . . . . . . . . .   8
     3.4.  New Event Condition: BecomesEqualTo . . . . . . . . . . .  10
     3.5.  LFB Properties  . . . . . . . . . . . . . . . . . . . . .  11
     3.6.  LFB class inheritance . . . . . . . . . . . . . . . . . .  12
     3.7.  Enhancing XML Validation  . . . . . . . . . . . . . . . .  13
   4.  XML Extension Schema for LFB Class Library Documents  . . . .  14
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  27
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  27
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  27
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  27
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  27
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  27
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  27

1.  Terminology and Conventions

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].

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1.2.  Definitions

   This document follows the terminology defined by the ForCES Model in
   [RFC5812].  The required definitions are repeated below for clarity.

      FE Model - The FE model is designed to model the logical
      processing functions of an FE.  The FE model proposed in this
      document includes three components; the LFB modeling of individual
      Logical Functional Block (LFB model), the logical interconnection
      between LFBs (LFB topology), and the FE-level attributes,
      including FE capabilities.  The FE model provides the basis to
      define the information elements exchanged between the CE and the
      FE in the ForCES protocol [RFC5810].

      LFB (Logical Functional Block) Class (or type) - A template that
      represents a fine-grained, logically separable aspect of FE
      processing.  Most LFBs relate to packet processing in the data
      path.  LFB classes are the basic building blocks of the FE model.

      LFB Instance - As a packet flows through an FE along a data path,
      it flows through one or multiple LFB instances, where each LFB is
      an instance of a specific LFB class.  Multiple instances of the
      same LFB class can be present in an FE's data path.  Note that we
      often refer to LFBs without distinguishing between an LFB class
      and LFB instance when we believe the implied reference is obvious
      for the given context.

      LFB Model - The LFB model describes the content and structures in
      an LFB, plus the associated data definition.  XML is used to
      provide a formal definition of the necessary structures for the
      modeling.  Four types of information are defined in the LFB model.
      The core part of the LFB model is the LFB class definitions; the
      other three types of information define constructs associated with
      and used by the class definition.  These are reusable data types,
      supported frame (packet) formats, and metadata.

      Element - Element is generally used in this document in accordance
      with the XML usage of the term.  It refers to an XML tagged part
      of an XML document.  For a precise definition, please see the full
      set of XML specifications from the W3C. This term is included in
      this list for completeness because the ForCES formal model uses
      XML.

      Attribute - Attribute is used in the ForCES formal modeling in
      accordance with standard XML usage of the term, i.e., to provide
      attribute information included in an XML tag.

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      LFB Metadata - Metadata is used to communicate per-packet state
      from one LFB to another, but is not sent across the network.  The
      FE model defines how such metadata is identified, produced, and
      consumed by the LFBs, but not how the per-packet state is
      implemented within actual hardware.  Metadata is sent between the
      FE and the CE on redirect packets.

      ForCES Component - A ForCES Component is a well-defined, uniquely
      identifiable and addressable ForCES model building block.  A
      component has a 32-bit ID, name, type, and an optional synopsis
      description.  These are often referred to simply as components.
      LFB Component - An LFB component is a ForCES component that
      defines the Operational parameters of the LFBs that must be
      visible to the CEs.

      LFB Class Library - The LFB class library is a set of LFB classes
      that has been identified as the most common functions found in
      most FEs and hence should be defined first by the ForCES Working
      Group.

2.  Introduction

   The ForCES Model [RFC5812] presents a formal way to define FEs
   Logical Function Blocks (LFBs) using 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.

   Specifically this document extends the ForCES Model to allow complex
   datatypes for metadata, optional default values for datatypes,
   optional access types for structures and fixes an issue with the LFB
   inheritance.  Additionally the document introduces two new features a
   new event condition BecomesEqualTo and LFB properties.

   These extensions are an addendum 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.

3.  ForCES Model Extension proposal

3.1.  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.

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

   1.  The Action Set metadata follows a packet inside the Flow Tables.
       The Action Set metadata is an array of actions to be performed at
       the end of the pipeline.

   2.  When a packet is received from a controller it may be accompanied
       by a list of actions to be performed on it prior to be sent on
       the flow table pipeline which 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.

       <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

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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

3.2.  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 optionally 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 Defintion 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 it appends to the declaration of the AtomicType this xml
   (Figure 5) to allow default values to Atomic datatypes.

      <xsd:element name="defaultValue" type="xsd:token" minOccurs="0"/>

     Figure 5: Appending xml in of AtomicType Definition in the schema

            <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 6: Example of optional default values

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3.3.  Optional Access Type for Structs

   In the original schema, the access type can be only be defined on
   components of LFB and not on components in structs or arrays.
   However when it's a struct datatype it is not possible to fine-tune
   access type per component in 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.

   With this extension is it allowed to define the access type for a
   struct component either in the datatype definitions or in the LFB
   component definitions.

   When the optional access type for a struct component is defined it
   MUST override the access type of the struct.  If by accident an
   access type for a component in a capability is defined, the access
   type MUST NOT be taken into account and MUST always be considered as
   read-only.

   This extension alters the definition of the struct in the xml schema
   from Figure 7 to Figure 8.

       <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 7: 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 8: New xml for the struct definition in the schema

            <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 9: Example of optional access types for struct

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3.4.  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 is exactly that of the BecomesEqualTo,
   the event is triggered.  This event condition is particular useful
   when there is a need to monitor one or more states of an LFB or the
   FE.  For example in the CEHA [I-D.ietf-forces-ceha] document 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 and MUST NOT
   generate 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 10: New Excerpt of BecomesEqualTo event condition definition
                               in the schema

   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 must also take into account to use count or time
   filtering to avoid being overrun by messages, e.g. in the case of
   rapid state changes.

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3.5.  LFB Properties

   The current model definition specifies properties for components of
   LFBs.  Experience however has proven valuable at least for debug
   reasons, to have statistics per LFB instance to monitor sent/received
   messages and errors for communication between CE and FE.  These
   properties are read-only.

   In order to avoid ambiguity on protocol path semantics, this document
   reserves LFB component 0 for LFB properties.  This reservation is
   backwards compatible as no LFB definition uses LFB component 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 11: Initial xml for LFB Component IDs

                <!-- 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 12: New xml for the disallowing 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>

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               </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>
               </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

3.6.  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 may inherit.  Recent implementations have identified an issue
   where ambiguity rises when different versions of an LFB class exists.
   This document augments the derivedFrom part of the LFB class
   definition with a mandatory version attribute when the derivedFrom
   field is used.

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   This extension alters the definition of the derivedFrom in the xml
   schema from Figure 13 to Figure 14.

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

           Figure 13: Initial xml for the LFB class inheritance

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

             Figure 14: New xml for the LFB class inheritance

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

      Figure 15: Example of use of new xml for LFB class Inheritance

3.7.  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.

   The following validation rules have been appended 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.

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4.  XML Extension Schema for LFB Class Library Documents

<?xml version="1.0" encoding="UTF-8"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
   xmlns="urn:ietf:params:xml:ns:forces:lfbmodel:1.0"
   xmlns:lfb="urn:ietf:params:xml:ns:forces:lfbmodel:1.0"
   targetNamespace="urn:ietf:params:xml:ns:forces:lfbmodel:1.0"
   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>

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      <xsd:key name="metadataDefID">
         <xsd:selector xpath="lfb:metadataDefs/lfb:metadataDef"/>
         <xsd:field xpath="lfb:metadataID"/>
      </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>

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   </xsd:complexType>
   <!-- Predefined (built-in) atomic data-types are: char, uchar,
   int16, uint16, int32, uint32, int64, uint64, string[N], string,
   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>

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         <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>
   </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">

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            <xsd:complexType>
               <xsd:sequence>
                  <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>

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   </xsd:complexType>
   <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"/>
                     <!-- 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">

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                    <xsd:complexType>
                      <xsd:simpleContent>
                        <xsd:extension base="xsd:NMTOKEN">
                          <xsd:attribute name="version"
                            type="versionType" use="required"/>
                        </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">

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               <xsd:selector xpath="lfb:capabilities/lfb:capability"/>
               <xsd:field xpath="@componentID"/>
            </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">

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                  <!--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: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">

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      <xsd:sequence>
         <xsd:element name="name" type="xsd:NMTOKEN"/>
         <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"/>

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      </xsd:choice>
   </xsd:complexType>
   <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>

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      </xsd:sequence>
   </xsd:complexType>
   <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>

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      </xsd:sequence>
      <xsd:attribute name="baseID" type="xsd:integer"
         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>

                           OpenFlow XML Library

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5.  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.

6.  IANA Considerations

   This specification requests that LFB Component ID 0 to be reserved.

7.  Security Considerations

   The security considerations that have been described in the ForCES
   Model RFC [RFC5812] apply to this document as well.

8.  References

8.1.  Normative References

   [I-D.ietf-forces-ceha]
              Ogawa, K., Wang, W., Haleplidis, E., and J. Salim, "ForCES
              Intra-NE High Availability", draft-ietf-forces-ceha-08
              (work in progress), October 2013.

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

   [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.

8.2.  Informative References

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

Author's Address

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

   Email: ehalep@ece.upatras.gr

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