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Versions: 00 01 02 03 04 05 rfc3688                Best Current Practice
Network Working Group                                        M. Mealling
Internet-Draft                                            VeriSign, Inc.
Expires: December 16, 2003                                 June 17, 2003

                         The IETF XML Registry

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
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   This Internet-Draft will expire on December 16, 2003.

Copyright Notice

   Copyright (C) The Internet Society (2003). All Rights Reserved.


   This document describes an IANA maintained registry for IETF
   standards which use Extensivle Markup Language (XML) related items
   such as Namespaces, Document Type Declarations (DTDs), Schemas, and
   Resource Description Framework (RDF) Schemas.

1. Introduction

   Over the past few years the Extensible Markup Language (XML)
   [W3C.REC-xml] has become a widely used method for data markup. There
   have already been several IETF Working Groups that have produced
   standards that define XML Document Type Definitions (DTDs), XML
   Namespaces [W3C.REC-xml-names] and XML Schemas [W3C.REC-xmlschema-1].
   Each one of these technologies uses Uniform Resource Identifiers

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   (URIs) [RFC2396] and other standardized identifiers to identify
   various components.

   For example, while it has been the practice within some standards
   that use Document Type Definitions (DTDs) to forego the use of the
   PUBLIC identifiers in favor of 'well known' SYSTEM identifiers, it
   has proven to be more trouble than its worth to attempt to
   standardize SYSTEM identifiers. The result is that several IETF
   standards that have simply created non-resolvable URIs in order to
   simply identify but not resolve the DTD for some given XML document.

   This document seeks to standardize and improve these practices by
   creating an IANA maintained registry of XML element identifiers so
   that document authors and implementors have a well maintained and
   authoritative location for their XML elements. As part of this
   standard, the IANA will maintain

   o  the public representation of the document,

   o  the URI for the elements if one is provided at the time of

   o  a registry of Public Identifiers as URIs.

   In the case where the registrant does not request a particular URI,
   the IANA will assign it a Uniform Resource Name that follows

2. Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119.

3. Registerable Documents

3.1 The Assigned/Registered URI

   All elements (except PUBLIC identifiers) in this registry will
   require a URI in order to be registered. If the registrant wishes to
   have a URI assigned  then a URN of the form:


    will be assigned where <class> is the type of the document being
   registered (see below).  <id> is a unique id generated by the IANA
   based on any means the IANA deems necessary to maintain uniqueness

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   and persistence. NOTE: in order for a URN of this type to be
   assigned, the item being registered MUST have been through the IETF
   concensus process. Practically this means it must be documented in an
   RFC. The RFC XXXX [RFCXXXX] URN registration template is found in
   Section 6.

   The IANA will also maintain a file server available via at least HTTP
   and FTP that contains all of the registered elements in some publicly
   accessible file space in the same way that all of the IANA's
   registered elements are available via
   http://www.iana.org/assignments/.  While the directory structure of
   this server is up to the IANA, it is suggested that the files be
   organized by the <class> and the individual files have the <id> as
   their filename.

   Implementors are warned that they should not programatically rely on
   those resources being available or the directory structure remaining
   static for any reason. It is explicitly recognized that some software
   tools attempt to download DTDs, schema, etc 'on the fly' and that
   developers should understand when this is done and to not reference
   IANA network resources as a 'schema download repository'. This is the
   reason that the IANA will not register or provide SYSTEM identifiers.

3.2 Registerable Classes

   The list of types of XML elements that can be registered with the
   IANA are:

   publicid -- An XML document that contains a DOCTYPE declaration or
      any other external reference can identify that reference via both
      a PUBLIC identifier and a SYSTEM identifier. The SYSTEM identifier
      is system-specific information that enables the entity manager of
      an XML system to locate the file, memory location, or pointer
      within a file where the entity can be found. It should also be
      noted that a system identifier could be an invocation of a program
      that controls access to an entity that is being identified. Thus
      they are not registered items. In many cases, SYSTEM identifiers
      are also URIs but in these cases the URI is still only used for
      system-specific information. In the case where a PUBLIC Identifier
      is also a URI it is possible for the SYSTEM Identifier to contain
      the same URI but this behavior is not recommended unless its side
      effects are well known and understood to not cause any
      unacceptable harm.

      A PUBLIC identifier is a name that is intended to be meaningful
      across systems and different user environments.  Typically it will
      be a name that has a registered owner associated with it, so that
      public identifiers will be guaranteed unique and no two entities

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      will have the same public identifier. In practice, PUBLIC
      identifiers are typically Formal Public Identifers [ISO.8879.1986]
      but they are not restricted to just that set. As said in

         "Any string which consists only of the public identifier
         characters (defined by Production 13 of Extensible Markup
         Language (XML) 1.0 Second Edition) is a legal public

       Therefore it is legal for a PUBLIC identifier to be a URN if it
      adheres to the character set restrictions.

      Thus, the identifier registered along with a DTD is its PUBLIC
      identifier. The only restriction being that it must adhere to the
      character set restrictions. In the case where the registrant does
      not provide one, the IANA will assign one of the form
      'urn:ietf:params:xml:pi:<id>'. Registrants are encouraged to
      investigate RFC  3151 [RFC3151] as a recommended method for
      minting a URN that can also be represented as an FPI.

   ns -- XML Namespaces [W3C.REC-xml-names] are named by a URI. They
      have no real, machine-parseable representation. Thus the
      registered document will be either the specification or a
      reference to it. In the case where a URI is not provided by the
      registrant, the IANA will assign a URN of the form
      'urn:ietf:params:xml:ns:<id> which will be the XML Namespace's

   schema -- XML Schemas [W3C.REC-xmlschema-1] are also identified by a
      URI but their contents are machine parseable. The IANA registered
      document will be the XML Schema file. The URN the IANA assigns can
      be used as the URI for the schema and is of the form

   rdfschema -- The Resource Description Format (RDF)
      [W3C.CR-rdf-schema] is an XML serialization of a connected graph
      based data model used for metadata expression. RDF makes use of
      schemas for RDF that express grammars about relationships between
      URIs. These grammars are identified by URIs. The URN assigned by
      the IANA can be used as the identifying URI and is of the form

4. Registration Procedures

   Until such time as the IANA requests or implements an automated
   process for the registration of these elements, any specifications

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   wishing to do so must make that request part of the IANA
   considerations section of their respective documents. That request
   must be in the form of the following template:

      The URI or PUBLIC identifier that identifies the XML component.
      If the registrant is requesting that the IANA assign a URI then
      this field should be specified as "please assign"

   Registrant Contact
      The individual/organization that is the registration contact for
      the component being registered. Ideally this will be the name and
      pertinent physical and network contact information. In the case of
      IETF developed standards the Registrant will be the IESG.

      The exact XML to be stored in the registry. Unless otherwise
      obvious what the beginning and end of the file are, the document
      should use the text "BEGIN" to mark the beginning of the file and
      "END" to mark the end of the file. The IANA will insert any text
      between those two strings (minus any page breaks and RFC
      formatting inserted by the RFC Editor) into the file kept in the

5. Security Considerations

   The information maintained by the IANA will be authoritative and thus
   will be a target for attack. In some cases, such as XML Schema and
   DTDs, the content maintained by the IANA may be directly input into
   software. Thus, extra care should be taken by the IANA to maintain
   the security precautions required for an important reference location
   for the Internet.

   Beyond this concern there are no other security considerations not
   already found with any other IANA registry.

6. IANA Considerations

   This documents seeks to create a rather large registry for which the
   IANA (at the direction of the IESG) will be primarily responsible.
   The amount of effort required to maintain this registry is not
   insignificant and the policies and procedures surrounding any
   approval process are non-trivial. The registry is on a First Come
   First Served basis but at this time a Specification is Required. Once
   the IETF has some experience with this registry these policies may

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   RFC XXXX [RFCXXXX] specifies that any new registry that requires a
   name to be assigned below the 'urn:ietf:params' namespace must
   specify the structure of that space in template form. The IANA is
   directed to create and maintain this new sub-namespace:

   Registry-name: xml

   Specification: This document contains the registry specification. The
      namespace is organized with one sub-namespace which is the <id>.

   Repository: To be assigned according to the guidelines found above.

   Index value: The class name

Normative References

              International Organization for Standardization,
              "Information processing - Text and office systems -
              Standard generalized markup language (SGML)", ISO Standard
              8879, 1986.

   [RFC2396]  Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
              Resource Identifiers (URI): Generic Syntax", RFC 2396,
              August 1998.

   [RFC3151]  Walsh, N., Cowan, J. and P. Grosso, "A URN Namespace for
              Public Identifiers", RFC 3151, August 2001.

   [RFCXXXX]  Mealling, M., Masinter, L., Hardie, T. and G. Klyne, "An
              IETF URN Sub-namespace for Registered Protocol
              Parameters", draft-mealling-iana-urn-02.txt (work in
              progress), August 2001.

              Brickley, D. and R. Guha, "Resource Description Framework
              (RDF) Schema Specification 1.0", W3C CR-rdf-schema, March
              2000, <http://www.w3.org/TR/2000/CR-rdf-schema-20000327>.

              Bray, T., Paoli, J., Sperberg-McQueen, C. and E. Maler,
              "Extensible Markup Language (XML) 1.0 (2nd ed)", W3C
              REC-xml, October 2000, <http://www.w3.org/TR/REC-xml>.

              Bray, T., Hollander, D. and A. Layman, "Namespaces in
              XML", W3C REC-xml-names, January 1999, <http://www.w3.org/

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              Thompson, H., Beech, D., Maloney, M. and N. Mendelsohn,
              "XML Schema Part 1: Structures", W3C REC-xmlschema-1, May
              2001, <http://www.w3.org/TR/xmlschema-1/>.

Author's Address

   Michael Mealling
   VeriSign, Inc.

   Mountain View, CA

   URI:   http://www.research.verisignlabs.com

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   Funding for the RFC Editor function is currently provided by the
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