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rfc:rfc3688

Network Working Group M. Mealling Request for Comments: 3688 VeriSign, Inc. BCP: 81 January 2004 Category: Best Current Practice

                       The IETF XML Registry

Status of this Memo

 This document specifies an Internet Best Current Practices for the
 Internet Community, and requests discussion and suggestions for
 improvements.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2004).  All Rights Reserved.

Abstract

 This document describes an IANA maintained registry for IETF
 standards which use Extensible 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
 (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

Mealling Best Current Practice [Page 1] RFC 3688 The IETF XML Registry January 2004

 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
    registration,
 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 (URN) that follows
 [RFC3553].

2. Terminology

 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 BCP 14, RFC 2119
 [RFC2119].

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
    urn:ietf:params:xml:<class>:<id>
 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
 and persistence.  NOTE: in order for a URN of this type to be
 assigned, the item being registered MUST have been through the IETF
 consensus process.  Basically, this means that it must be documented
 in a RFC.  The RFC 3553 [RFC3553] 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.

Mealling Best Current Practice [Page 2] RFC 3688 The IETF XML Registry January 2004

 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 when 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.  However, 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 will have the same public identifier.  In practice,
    PUBLIC identifiers are typically Formal Public Identifiers
    [ISO.8879.1986] but they are not restricted to just that set.  As
    said in [RFC3151]:
       "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
       identifier."
    Therefore, it is legal for a PUBLIC identifier to be a URN if it
    adheres to the character set restrictions.

Mealling Best Current Practice [Page 3] RFC 3688 The IETF XML Registry January 2004

    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
    name.
 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
    'urn:ietf:params:xml:schema:<id>'.
 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
    'urn:ietf:params:xml:rdfschema:<id>'.

4. Registration Procedures

 Until the IANA requests or implements an automated process for the
 registration of these elements, any specifications 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:
 URI
    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.

Mealling Best Current Practice [Page 4] RFC 3688 The IETF XML Registry January 2004

 XML
    The exact XML to be stored in the registry.  Unless the beginning
    and end of the file is obvious, 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 repository.

5. Security Considerations

 The information maintained by the IANA will be authoritative and 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 document 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 a Specification is Required.  Once the IETF
 has some experience with this registry, these policies may change.
 RFC 3553 [RFC3553] specifies that any new registry requiring a name,
 to be assigned below the 'urn:ietf:params' namespace and must specify
 the structure of that space in template form.  The IANA has created
 and will 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

Mealling Best Current Practice [Page 5] RFC 3688 The IETF XML Registry January 2004

7. Normative References

 [ISO.8879.1986]       International Organization for Standardization,
                       "Information processing - Text and office
                       systems - Standard generalized markup language
                       (SGML)", ISO Standard 8879, 1986.
 [RFC2119]             Bradner, S., "Key words for use in RFCs to
                       Indicate Requirement Levels", BCP 14, RFC 2119,
                       March 1997.
 [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.
 [RFC3553]             Mealling, M., Masinter, L., Hardie, T. and G.
                       Klyne, "An IETF URN Sub-namespace for
                       Registered Protocol Parameters", BCP 73, RFC
                       3553, June 2003.
 [W3C.CR-rdf-schema]   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>.
 [W3C.REC-xml]         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>.
 [W3C.REC-xml-names]   Bray, T., Hollander, D. and A. Layman,
                       "Namespaces in XML", W3C REC-xml-names, January
                       1999, <http://www.w3.org/TR/REC-xml-names>.
 [W3C.REC-xmlschema-1] 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/>.

Mealling Best Current Practice [Page 6] RFC 3688 The IETF XML Registry January 2004

8. Intellectual Property Statement

 The IETF takes no position regarding the validity or scope of any
 intellectual property or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
 this document or the extent to which any license under such rights
 might or might not be available; neither does it represent that it
 has made any effort to identify any such rights.  Information on the
 IETF's procedures with respect to rights in standards-track and
 standards-related documentation can be found in BCP-11.  Copies of
 claims of rights made available for publication and any assurances of
 licenses to be made available, or the result of an attempt made to
 obtain a general license or permission for the use of such
 proprietary rights by implementors or users of this specification can
 be obtained from the IETF Secretariat.
 The IETF invites any interested party to bring to its attention any
 copyrights, patents or patent applications, or other proprietary
 rights which may cover technology that may be required to practice
 this standard.  Please address the information to the IETF Executive
 Director.

9. Author's Address

 Michael Mealling
 VeriSign, Inc.
 Mountain View, CA
 USA
 EMail: michael@verisignlabs.com
 URI:   http://www.research.verisignlabs.com

Mealling Best Current Practice [Page 7] RFC 3688 The IETF XML Registry January 2004

10. Full Copyright Statement

 Copyright (C) The Internet Society (2004).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assignees.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Mealling Best Current Practice [Page 8]

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