Network Working Group                                   J. Schoenwaelder

Internet-Draft                                                F. Strauss

Expires: July 10, 2002                                   TU Braunschweig

                                                         January 9, 2002

                 Using XML to Exchange SMI Definitions

                       draft-irtf-nmrg-smi-xml-01

Status of this Memo

   This document is an Internet-Draft and is in full conformance with

   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering

   Task Force (IETF), its areas, and its working groups.  Note that

   other groups may also distribute working documents as Internet-

   Drafts.

   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."

   The list of current Internet-Drafts can be accessed at

   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at

   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on July 10, 2002.

Copyright Notice

   Copyright (C) The Internet Society (2002).  All Rights Reserved.

Abstract

   This memo describes how the Extensible Markup Language (XML) can be

   used to exchange SMIv1 and SMIv2 definitions between XML enabled

   applications.

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Table of Contents

   1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . .   3

   2. SMI XML Schema . . . . . . . . . . . . . . . . . . . . . . . .   4

   3. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . .  16

   4. Open Issues  . . . . . . . . . . . . . . . . . . . . . . . . .  16

   5. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . .  16

      References . . . . . . . . . . . . . . . . . . . . . . . . . .  16

      Authors' Addresses . . . . . . . . . . . . . . . . . . . . . .  17

      Full Copyright Statement . . . . . . . . . . . . . . . . . . .  18

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1. Introduction

   This memo describes how the Extensible Markup Language (XML) [1] can

   be used to exchange SMIv1 [2][3][4] and SMIv2 [5][6][7] definitions

   between XML enabled applications.  The acronym SMI is used throughout

   this document as a version neutral name for SMIv1 or SMIv2.

   The XML Schema defined in this memo allows applications with embedded

   generic XML parsers to read (or edit) the original SMI definitions.

   The XML Schema is optimized for this purpose.  Terseness of the XML

   output was of minimal importance since humans are expected to read

   the originial SMI definitions.

   In fact, the XML format of an SMI module is significantly longer

   compared to the original SMI definition.  This is in line with the

   design goals for XML, which favours computer readability over

   terseness.

   There are several scenarios where an XML representation of SMI

   definitions is useful:

   o  The XML format may be used as an intermediate format between a

      validating SMI compiler/parser and post processing tools such as

      code or schema generators.  (The undocumented mosy format has been

      used in the past for this purpose.  The mosy format does not

      preserve all information present in a SMI module and is therefore

      problematic.)

   o  The XML format can be used with XSLT post processors to generate

      documentation in various formats.

   o  The XML format makes it possible to access SMI definitions from a

      variety of programming languages.  E.g., XML parsers are available

      in Java, C, C++, Tcl, Perl, Python, and GNU Emacs Lisp in both

      commercial and open source forms.

   o  There are generic tools for maintaining large sets of XML

      definitions.  This includes tools to search for definitions with a

      specific property.  Such generic XML tools can be very useful in

      organizations that must maintain large amounts of SMI definitions.

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2. SMI XML Schema

   <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">

      - The top-level element.

      -

     -->

    <xsd:element name="smi">

     <xsd:complexType>

      <xsd:sequence>

       <xsd:element ref="module"/>

       <xsd:element ref="imports"       minOccurs="0" maxOccurs="unbounded"/>

       <xsd:element ref="typedefs"      minOccurs="0" maxOccurs="unbounded"/>

       <xsd:element ref="nodes"         minOccurs="0" maxOccurs="unbounded"/>

       <xsd:element ref="notifications" minOccurs="0" maxOccurs="unbounded"/>

       <xsd:element ref="groups"        minOccurs="0" maxOccurs="unbounded"/>

       <xsd:element ref="compliances"   minOccurs="0" maxOccurs="unbounded"/>

      </xsd:sequence>

     </xsd:complexType>

    </xsd:element>

      - Terminal Elements.

      -

     -->

    <xsd:element name="description">

     <xsd:simpleType>

      <xsd:restriction base="xsd:string"/>

     </xsd:simpleType>

    </xsd:element>

    <xsd:element name="reference">

     <xsd:simpleType>

      <xsd:restriction base="xsd:string"/>

     </xsd:simpleType>

    </xsd:element>

    <xsd:element name="format">

     <xsd:simpleType>

      <xsd:restriction base="xsd:string"/>

     </xsd:simpleType>

    </xsd:element>

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    <xsd:element name="units">

     <xsd:simpleType>

      <xsd:restriction base="xsd:string"/>

     </xsd:simpleType>

    </xsd:element>

    <xsd:element name="default">

     <xsd:simpleType>

      <xsd:restriction base="xsd:string"/>

     </xsd:simpleType>

    </xsd:element>

    <xsd:element name="access">

     <xsd:simpleType>

      <xsd:restriction base="xsd:string">

       <xsd:enumeration value="noaccess"/>

       <xsd:enumeration value="notifyonly"/>

       <xsd:enumeration value="readonly"/>

       <xsd:enumeration value="readwrite"/>

      </xsd:restriction>

     </xsd:simpleType>

    </xsd:element>

    <xsd:element name="range">

     <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:element name="namednumber">

     <xsd:complexType>

      <xsd:attribute name="name"   type="xsd:string"  use="required"/>

      <xsd:attribute name="number" type="xsd:integer" use="required"/>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="parent">

     <xsd:complexType>

      <xsd:attribute name="module" type="xsd:string" use="required"/>

      <xsd:attribute name="name"   type="xsd:string" use="required"/>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="type">

     <xsd:complexType>

      <xsd:attribute name="module" type="xsd:string" use="required"/>

      <xsd:attribute name="name"   type="xsd:string" use="required"/>

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     </xsd:complexType>

    </xsd:element>

    <xsd:element name="syntax">

     <xsd:complexType>

      <xsd:choice>

       <xsd:element ref="type"/>

       <xsd:element ref="typedef"/>

      </xsd:choice>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="writesyntax">

     <xsd:complexType>

      <xsd:choice>

       <xsd:element ref="type"/>

       <xsd:element ref="typedef"/>

      </xsd:choice>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="linkage">

     <xsd:complexType>

      <xsd:choice>

       <xsd:element ref="index" minOccurs="1" maxOccurs="unbounded"/>

       <xsd:element ref="augments"/>

       <xsd:element ref="reorders"/>

       <xsd:element ref="sparse"/>

       <xsd:element ref="expands"/>

      </xsd:choice>

      <xsd:attribute name="implied" default="false">

       <xsd:simpleType>

        <xsd:restriction base="xsd:string">

         <xsd:enumeration value="true"/>

         <xsd:enumeration value="false"/>

        </xsd:restriction>

       </xsd:simpleType>

      </xsd:attribute>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="index">

     <xsd:complexType>

      <xsd:attribute name="module" type="xsd:string" use="required"/>

      <xsd:attribute name="name"   type="xsd:string" use="required"/>

     </xsd:complexType>

    </xsd:element>

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    <xsd:element name="augments">

     <xsd:complexType>

      <xsd:attribute name="module" type="xsd:string" use="required"/>

      <xsd:attribute name="name"   type="xsd:string" use="required"/>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="reorders">

     <xsd:complexType>

      <xsd:attribute name="module" type="xsd:string" use="required"/>

      <xsd:attribute name="name"   type="xsd:string" use="required"/>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="sparse">

     <xsd:complexType>

      <xsd:attribute name="module" type="xsd:string" use="required"/>

      <xsd:attribute name="name"   type="xsd:string" use="required"/>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="expands">

     <xsd:complexType>

      <xsd:attribute name="module" type="xsd:string" use="required"/>

      <xsd:attribute name="name"   type="xsd:string" use="required"/>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="module">

     <xsd:complexType>

      <xsd:sequence>

       <xsd:element ref="organization" minOccurs="0" maxOccurs="1"/>

       <xsd:element ref="contact"      minOccurs="0" maxOccurs="1"/>

       <xsd:element ref="description"  minOccurs="0" maxOccurs="1"/>

       <xsd:element ref="reference"    minOccurs="0" maxOccurs="1"/>

       <xsd:element ref="revision"     minOccurs="0" maxOccurs="unbounded"/>

       <xsd:element ref="identity"     minOccurs="0" maxOccurs="1"/>

      </xsd:sequence>

      <xsd:attribute name="name"     type="xsd:string" use="required"/>

      <xsd:attribute name="language"                   use="required">

       <xsd:simpleType>

        <xsd:restriction base="xsd:string">

         <xsd:enumeration value="SMIv1"/>

         <xsd:enumeration value="SMIv2"/>

         <xsd:enumeration value="SMIng"/>

        </xsd:restriction>

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       </xsd:simpleType>

      </xsd:attribute>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="organization">

     <xsd:simpleType>

      <xsd:restriction base="xsd:string"/>

     </xsd:simpleType>

    </xsd:element>

    <xsd:element name="contact">

     <xsd:simpleType>

      <xsd:restriction base="xsd:string"/>

     </xsd:simpleType>

    </xsd:element>

    <xsd:element name="revision">

     <xsd:complexType>

      <xsd:sequence>

       <xsd:element ref="description"/>

      </xsd:sequence>

      <xsd:attribute name="date" type="xsd:string" use="required"/>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="identity">

     <xsd:complexType>

      <xsd:attribute name="node" type="xsd:string" use="required"/>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="imports">

     <xsd:complexType>

      <xsd:sequence>

       <xsd:element ref="import" maxOccurs="unbounded"/>

      </xsd:sequence>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="import">

     <xsd:complexType>

      <xsd:attribute name="module" type="xsd:string" use="required"/>

      <xsd:attribute name="name"   type="xsd:string" use="required"/>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="typedefs">

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     <xsd:complexType>

      <xsd:sequence>

       <xsd:element ref="typedef" maxOccurs="unbounded"/>

      </xsd:sequence>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="typedef">

     <xsd:complexType>

      <xsd:sequence>

       <xsd:element ref="parent"      minOccurs="0" maxOccurs="1"/>

       <xsd:element ref="range"       minOccurs="0" maxOccurs="unbounded"/>

       <xsd:element ref="namednumber" minOccurs="0" maxOccurs="unbounded"/>

       <xsd:element ref="default"     minOccurs="0" maxOccurs="1"/>

       <xsd:element ref="format"      minOccurs="0" maxOccurs="1"/>

       <xsd:element ref="units"       minOccurs="0" maxOccurs="1"/>

       <xsd:element ref="description" minOccurs="0" maxOccurs="1"/>

       <xsd:element ref="reference"   minOccurs="0" maxOccurs="1"/>

      </xsd:sequence>

      <xsd:attribute name="name"     type="xsd:string" default=""/>

      <xsd:attribute name="basetype" type="xsd:string" use="required"/>

      <xsd:attribute name="status"                     default="current">

       <xsd:simpleType>

        <xsd:restriction base="xsd:string">

         <xsd:enumeration value="current"/>

         <xsd:enumeration value="deprecated"/>

         <xsd:enumeration value="obsolete"/>

         <xsd:enumeration value="mandatory"/>

         <xsd:enumeration value="optional"/>

        </xsd:restriction>

       </xsd:simpleType>

      </xsd:attribute>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="nodes">

     <xsd:complexType>

      <xsd:choice maxOccurs="unbounded">

       <xsd:element ref="node"/>

       <xsd:element ref="scalar"/>

       <xsd:element ref="table"/>

      </xsd:choice>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="node">

     <xsd:complexType>

      <xsd:sequence>

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       <xsd:element ref="description" minOccurs="0" maxOccurs="1"/>

      </xsd:sequence>

      <xsd:attribute name="name"   type="xsd:string" use="required"/>

      <xsd:attribute name="oid"    type="xsd:string" use="required"/>

      <xsd:attribute name="status" default="current">

       <xsd:simpleType>

        <xsd:restriction base="xsd:string">

         <xsd:enumeration value="current"/>

         <xsd:enumeration value="deprecated"/>

         <xsd:enumeration value="obsolete"/>

         <xsd:enumeration value="mandatory"/>

         <xsd:enumeration value="optional"/>

        </xsd:restriction>

       </xsd:simpleType>

      </xsd:attribute>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="scalar">

     <xsd:complexType>

      <xsd:sequence>

       <xsd:element ref="syntax"/>

       <xsd:element ref="access"/>

       <xsd:element ref="default"    minOccurs="0" maxOccurs="1"/>

       <xsd:element ref="format"     minOccurs="0" maxOccurs="1"/>

       <xsd:element ref="units"      minOccurs="0" maxOccurs="1"/>

       <xsd:element ref="description"/>

       <xsd:element ref="reference"  minOccurs="0" maxOccurs="1"/>

      </xsd:sequence>

      <xsd:attribute name="name"   type="xsd:string" use="required"/>

      <xsd:attribute name="oid"    type="xsd:string" use="required"/>

      <xsd:attribute name="status" default="current">

       <xsd:simpleType>

        <xsd:restriction base="xsd:string">

         <xsd:enumeration value="current"/>

         <xsd:enumeration value="deprecated"/>

         <xsd:enumeration value="obsolete"/>

         <xsd:enumeration value="mandatory"/>

         <xsd:enumeration value="optional"/>

        </xsd:restriction>

       </xsd:simpleType>

      </xsd:attribute>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="table">

     <xsd:complexType>

      <xsd:sequence>

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       <xsd:element ref="description"/>

       <xsd:element ref="reference" minOccurs="0" maxOccurs="1"/>

       <xsd:element ref="row"/>

      </xsd:sequence>

      <xsd:attribute name="name"   type="xsd:string" use="required"/>

      <xsd:attribute name="oid"    type="xsd:string" use="required"/>

      <xsd:attribute name="status" default="current">

       <xsd:simpleType>

        <xsd:restriction base="xsd:string">

         <xsd:enumeration value="current"/>

         <xsd:enumeration value="deprecated"/>

         <xsd:enumeration value="obsolete"/>

         <xsd:enumeration value="mandatory"/>

         <xsd:enumeration value="optional"/>

        </xsd:restriction>

       </xsd:simpleType>

      </xsd:attribute>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="row">

     <xsd:complexType>

      <xsd:sequence>

       <xsd:element ref="linkage"/>

       <xsd:element ref="description"/>

       <xsd:element ref="reference" minOccurs="0" maxOccurs="1"/>

       <xsd:element ref="column"    maxOccurs="unbounded"/>

      </xsd:sequence>

      <xsd:attribute name="name"   type="xsd:string" use="required"/>

      <xsd:attribute name="oid"    type="xsd:string" use="required"/>

      <xsd:attribute name="create" default="false">

       <xsd:simpleType>

        <xsd:restriction base="xsd:string">

         <xsd:enumeration value="true"/>

         <xsd:enumeration value="false"/>

        </xsd:restriction>

       </xsd:simpleType>

      </xsd:attribute>

      <xsd:attribute name="status" default="current">

       <xsd:simpleType>

        <xsd:restriction base="xsd:string">

         <xsd:enumeration value="current"/>

         <xsd:enumeration value="deprecated"/>

         <xsd:enumeration value="obsolete"/>

         <xsd:enumeration value="mandatory"/>

         <xsd:enumeration value="optional"/>

        </xsd:restriction>

       </xsd:simpleType>

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      </xsd:attribute>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="column">

     <xsd:complexType>

      <xsd:sequence>

       <xsd:element ref="syntax"/>

       <xsd:element ref="access"/>

       <xsd:element ref="default"   minOccurs="0" maxOccurs="1"/>

       <xsd:element ref="format"    minOccurs="0" maxOccurs="1"/>

       <xsd:element ref="units"     minOccurs="0" maxOccurs="1"/>

       <xsd:element ref="description"/>

       <xsd:element ref="reference" minOccurs="0" maxOccurs="1"/>

      </xsd:sequence>

      <xsd:attribute name="name" type="xsd:string" use="required"/>

      <xsd:attribute name="oid"  type="xsd:string" use="required"/>

      <xsd:attribute name="status" default="current">

       <xsd:simpleType>

        <xsd:restriction base="xsd:string">

         <xsd:enumeration value="current"/>

         <xsd:enumeration value="deprecated"/>

         <xsd:enumeration value="obsolete"/>

         <xsd:enumeration value="mandatory"/>

         <xsd:enumeration value="optional"/>

        </xsd:restriction>

       </xsd:simpleType>

      </xsd:attribute>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="notifications">

     <xsd:complexType>

      <xsd:sequence>

       <xsd:element ref="notification" maxOccurs="unbounded"/>

      </xsd:sequence>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="notification">

     <xsd:complexType>

      <xsd:sequence>

       <xsd:element ref="objects"/>

       <xsd:element ref="description"/>

       <xsd:element ref="reference" minOccurs="0" maxOccurs="1"/>

      </xsd:sequence>

      <xsd:attribute name="name" type="xsd:string" use="required"/>

      <xsd:attribute name="oid" type="xsd:string" use="required"/>

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      <xsd:attribute name="status" default="current">

       <xsd:simpleType>

        <xsd:restriction base="xsd:string">

         <xsd:enumeration value="current"/>

         <xsd:enumeration value="deprecated"/>

         <xsd:enumeration value="obsolete"/>

         <xsd:enumeration value="mandatory"/>

         <xsd:enumeration value="optional"/>

        </xsd:restriction>

       </xsd:simpleType>

      </xsd:attribute>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="objects">

     <xsd:complexType>

      <xsd:sequence>

       <xsd:element ref="object" maxOccurs="unbounded"/>

      </xsd:sequence>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="object">

     <xsd:complexType>

      <xsd:attribute name="module" type="xsd:string" use="required"/>

      <xsd:attribute name="name" type="xsd:string" use="required"/>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="groups">

     <xsd:complexType>

      <xsd:sequence>

       <xsd:element ref="group" maxOccurs="unbounded"/>

      </xsd:sequence>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="group">

     <xsd:complexType>

      <xsd:sequence>

       <xsd:element ref="members"/>

       <xsd:element ref="description"/>

       <xsd:element ref="reference" minOccurs="0" maxOccurs="1"/>

      </xsd:sequence>

      <xsd:attribute name="name" type="xsd:string" use="required"/>

      <xsd:attribute name="oid" type="xsd:string" use="required"/>

      <xsd:attribute name="status" default="current">

       <xsd:simpleType>

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        <xsd:restriction base="xsd:string">

         <xsd:enumeration value="current"/>

         <xsd:enumeration value="deprecated"/>

         <xsd:enumeration value="obsolete"/>

         <xsd:enumeration value="mandatory"/>

         <xsd:enumeration value="optional"/>

        </xsd:restriction>

       </xsd:simpleType>

      </xsd:attribute>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="members">

     <xsd:complexType>

      <xsd:sequence>

       <xsd:element ref="member" maxOccurs="unbounded"/>

      </xsd:sequence>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="member">

     <xsd:complexType>

      <xsd:attribute name="module" type="xsd:string" use="required"/>

      <xsd:attribute name="name" type="xsd:string" use="required"/>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="compliances">

     <xsd:complexType>

      <xsd:sequence>

       <xsd:element ref="compliance" maxOccurs="unbounded"/>

      </xsd:sequence>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="compliance">

     <xsd:complexType>

      <xsd:sequence>

       <xsd:element ref="description"/>

       <xsd:element ref="requires"/>

       <xsd:element ref="refinements" minOccurs="0" maxOccurs="1"/>

      </xsd:sequence>

      <xsd:attribute name="name" type="xsd:string" use="required"/>

      <xsd:attribute name="oid" type="xsd:string" use="required"/>

      <xsd:attribute name="status" default="current">

       <xsd:simpleType>

        <xsd:restriction base="xsd:string">

         <xsd:enumeration value="current"/>

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         <xsd:enumeration value="deprecated"/>

         <xsd:enumeration value="obsolete"/>

         <xsd:enumeration value="mandatory"/>

         <xsd:enumeration value="optional"/>

        </xsd:restriction>

       </xsd:simpleType>

      </xsd:attribute>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="requires">

     <xsd:complexType>

      <xsd:choice maxOccurs="unbounded">

       <xsd:element ref="mandatory"/>

       <xsd:element ref="option"/>

      </xsd:choice>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="mandatory">

     <xsd:complexType>

      <xsd:attribute name="module" type="xsd:string" use="required"/>

      <xsd:attribute name="name" type="xsd:string" use="required"/>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="option">

     <xsd:complexType>

      <xsd:sequence>

       <xsd:element ref="description"/>

      </xsd:sequence>

      <xsd:attribute name="module" type="xsd:string" use="required"/>

      <xsd:attribute name="name" type="xsd:string" use="required"/>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="refinements">

     <xsd:complexType>

      <xsd:sequence>

       <xsd:element ref="refinement" maxOccurs="unbounded"/>

      </xsd:sequence>

     </xsd:complexType>

    </xsd:element>

    <xsd:element name="refinement">

     <xsd:complexType>

      <xsd:sequence>

       <xsd:element ref="syntax" minOccurs="0" maxOccurs="1"/>

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       <xsd:element ref="access" minOccurs="0" maxOccurs="1"/>

       <xsd:element ref="description"/>

      </xsd:sequence>

      <xsd:attribute name="module" type="xsd:string" use="required"/>

      <xsd:attribute name="name" type="xsd:string" use="required"/>

     </xsd:complexType>

    </xsd:element>

   </xsd:schema>

3. Examples

4. Open Issues

      Shall we get rid of the identity element by making it an optional

      attribute of the module element?

5. Acknowledgments

   This document is the result of discussions within the Network

   Management Research Group (NMRG) of the Internet Research Task

   Force[8] (IRTF).

   Special thanks to Bert Helthuis, Atin Banerjee and Debnarayan Kar for

   providing useful feedback and access to their private SMI XML DTDs.

   A prototype implementation of an SMIv1/v2 converter to XML is freely

   available as part of the libsmi[9] SMI parser library distribution.

References

   [1]  World Wide Web Consortium, "Extensible Markup Language (XML) 1.0

        (Second Edition)", W3C REC-xml-20001006, October 2000.

   [2]  Rose, M. and K. McCloghrie, "Structure and identification of