ForCES Model Extension
draft-haleplidis-forces-model-extension-00

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 extensions without a need to alter the protocol while retaining backward compatibility with older xml libraries.

Status of This Memo

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

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

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

This Internet-Draft will expire on April 02, 2013.

Copyright Notice

Copyright (c) 2012 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. Terminology and Conventions
• 1.1. Requirements Language
• 1.2. Definitions
• 2. Introduction
• 3. ForCES Model Extension overview
• 4. Extensions
• 4.1. Complex Metadata
• 4.2. DataType and Metadata Optional Default Value
• 4.3. Optional Frame Produced
• 4.4. Strengthen XML Validation
• 5. XML Extension Schema for LFB Class Library Documents
• 6. Acknowledgements
• 7. IANA Considerations
• 8. Security Considerations
• 9. References
• 9.1. Normative References
• 9.2. Informative References
• Author's Address

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].

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.

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 litlte more than two years and current experience in its use has shown some room for adding new and changing existing modeling concepts.

This document extends the ForCES Model by changing and adding new concepts. These extensions 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 overview

The folowing extensions are considered:

1. Allow complex metadata.
2. Allow optional default values for datatypes and metadata.
3. Change from mandatory to optional the frame produced in the output port of LFBs.
4. Strengthen the XML validation.

4. Extensions

Some of these extensions were product of the work done on the OpenFlow library [I-D.haleplidis-forces-openflow-lib] document.

4.1. Complex Metadata

Section 4.6. (Element for Metadata Definitions) in the ForCES Model [RFC5812] limits the datatype use in metadata to only atomic types.

With this extension, complex data types are also allowed, specifically structs and arrays as metadata. A simple use case can be seen in the OpenFlow switch [OpenFlowSpec1.1] where exists the Action Set metadata which is an array.

4.2. DataType and Metadata Optional Default Value

In the original schema, default values can be defined only in datatypes defined inside LFB components. However when it's a complex datatype or it's a refered datatype, using the default value field is difficult to be used. Additionally there is no option in a complex datatype to use the default value field for only one component in the complex datatype.

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. The same applies to metadata.

4.3. Optional Frame Produced

In the original schema, frame expected in LFB inputs is optional, but frame produced in LFB outputs is mandatory. There is a case in the OpenFlow switch [OpenFlowSpec1.1] where the OpenFlow switch buffers the packet and sends only part of it to the controller with a Buffer ID as metadata. In this case the input port of the Redirect LFB will not expect any packets but only metadata. The LFB that performs the buffering will only send metadata and not the packet.

4.4. Strengthen XML Validation

The following validation rules have been inserted in the original schema in [RFC5812]:

1. Each metadata ID must be unique. This validation rule checks only within the xml file.
2. LFB Class IDs must be unique. This validataion rule checks only within the xml file.
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.

5. 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>
    <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>
  </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>
      <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">
        <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="componentID" type="xsd:unsignedInt"
           use="required"/>
        </xsd:complexType>
      </xsd:element>
    </xsd:sequence>
  </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>
              <!-- 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="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" type="xsd:NMTOKEN"
             minOccurs="0"/>
            <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"/>
        </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"/>
            <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"/>
      <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>
  <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>
          <xsd:attribute name="componentID" type="xsd:unsignedInt"
           use="required"/>
        </xsd:complexType>
      </xsd:element>
    </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>
    </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"/>
  <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>
 

6. Acknowledgements

TBD

7. IANA Considerations

This memo includes no request to IANA.

8. Security Considerations

TBD

9. References

9.1. Normative References

9.2. Informative References

Author's Address