Network Working Group M. Mealling
Internet-Draft VeriSign, Inc.
Expires: December 28, 2002 June 29, 2002
The IETF XML Registry
draft-mealling-iana-xmlns-registry-04.txt
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Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
This document describes an IANA maintained registry for IETF
standards which use XML related items such as Namespaces, DTD,
Schemas, and RDF Schemas.
1. Introduction
Over the past few years 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 DTDs, XML
Namespaces [W3C.REC-xml-names] and XML Schemas [W3C.REC-xmlschema-1].
Each one of these technologies uses URIs [RFC2396] and other
standardized identifiers to identify various components.
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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
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 that follows
[RFCXXXX].
2. Registerable Documents
2.1 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
concensus process. Practically this means it must be documented in
an RFC. The RFC XXXX [RFCXXXX] URN registration template is found in
Section 4.
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
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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.
2.2 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.
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 Identifers [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."
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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
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>'.
3. Registration Procedures
Until such time as the IANA requests or implements an automated
process for the registration of these elements, any specifications
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:
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
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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.
XML
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
repository.
4. 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 change.
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
[ISO.8879.1986] International Organization for
Standardization, "Information processing -
Text and office systems - Standard generalized
markup language (SGML)", ISO Standard 8879,
1986.
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[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.
[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/>.
Author's Address
Michael Mealling
VeriSign, Inc.
Mountain View, CA
US
URI: http://www.research.netsol.com
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