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.
AbstractThis 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. 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
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]. RFC2119]. 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.
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. 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.
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>'.
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. 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
[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/>.
Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society.