

Network Working Group                                      M. Nottingham
Internet-Draft                                               BEA Systems
Expires: May 1, 2004                                            M. Baker
                                                           November 2003


                 The 'uri' Media Type Registration Tree
                 draft-nottingham-uri-media-tree-00.xml

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

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   This Internet-Draft will expire on May 1, 2004.

Copyright Notice

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

Abstract

   This document specifies the 'uri' media subtype registration tree,
   which is intended to ease the deployment of new Internet applications
   with associated media types without being constrained by the
   necessity of a specialized central registry.  By using URIs, this
   tree also provides the (optional) added benefit of permitting the
   decentralized lookup of information associated with the media type.

1. Requirements notation

   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 [RFC2119].



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2. Introduction

   The registration procedures for Internet media types [RFC2048] allow
   for the specification of media type trees, which allow for faceted
   names to be described in order to increase the efficiency and
   flexibility of the registration process. They also allow for the
   creation of new registration trees, with the advice and consent of
   the IESG.

   This specification proposes one such tree for consideration.

3. Motivations

3.1 Decentralization

   A Registry of Assignments using Ubiquitous Technologies and Careful
   Policies" [RFC2048] was also an important motivation for the 'uri'
   tree.  It describes some of the shortcomings of registries which
   don't assign authoritative dereferenceable URIs for their
   assignments.

   It is an objective of the 'uri' subtree to achieve as many of the
   benefits of this approach as possible, while still fitting into the
   existing deployed media type based application dispatch framework.

3.2 XML

   The Internet media type system was designed to encourage certain
   properties, and arguably has been quite successful because of its
   approach. In particular, IANA acts as a central registry to bring
   coordination and convenience, and various levels of community review
   are required before a media type may be registered, to assure some
   level of quality in and appropriate application of media types.

   However, the advent of the Web and in particular XML has changed the
   conditions in which formats are created and used. XML allows the
   creation of business-specific document and protocol formats by end
   users, rather than standards organisations. Often, these end users
   are unfamiliar with IETF and IANA process for registration of media
   types, and do not have a requirement for recognition by a centralized
   registry. As such, the cost of media type registration for these
   users is not justified.

   As a result, many formats are created without corresponding media
   types (often under the umbrella of 'text/xml' or 'application/xml').
   Such formats are not first-class citizens on the Internet or the Web;
   one cannot content negotiate for them, for example, and one cannot
   use existing software dispatch mechanisms in MIME software to



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   accommodate them.

   It should be noted that these undesirable effects disproportionately
   affect those who wish to use the format in ways that may not have
   been forseen by its creators. As such, the registration system
   indirectly discourages the use of those mechanisms that leverage
   media types.

   Current registration proceedures do allow for some flexibility to
   accommodate vendor-specific formats (the .vnd tree), "vanity" formats
   (the .prs tree) and ad hoc, experimental formats (the x. tree and its
   predecessor, the 'x-' convention). Unfortunately, these mechanisms do
   not address the problems described here; the .vnd and .prs trees are
   still based on a centralized registry, and the x- convention is too
   brittle for most uses (and indeed its use has been discouraged for
   some time).

   This specification proposes that the widely deployed DNS
   infrastructure be leveraged to act as a distributed registry, to
   avoid the possibility of collision, whilst removing the need for an
   additional centralized registry. In this manner, it is similar to
   URIs, in that they also leverage the DNS to provide locally-managed
   name spaces.

4. The 'uri' Tree

   The 'uri' tree follows the conventions of faceted name trees as
   specified by [RFC2048], and is distinguished by the leading facet
   'uri.'. This facet MUST be followed by an absolute URI reference per
   [RFC2396], with the additional syntactic constraint that the URI
   cannot include an unescaped semi-colon (";"), as this would be
   interpreted by MIME agents as a delimiter between the media type and
   its attributes.

   Media types using this tree MUST be minted with the knowledge and
   permission of the authority identified by the authority component of
   the URI, if any.

4.1 Format-Specific Attributes

   Formats using this tree MAY designate their own attributes, which
   SHOULD be documented at or referenced from the URI facet of the type.

5. IANA Considerations

   Implementation of the uri tree does not require IANA coordination.





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6. Security Considerations

6.1 Change of Ownership

   Over time, the authority for the URI in a uri tree media type may
   change ownership. Without proper care, media types created by the
   previous owner might collide with those created by the new owner. As
   a result, when domains which have been used in the registration of
   media types in the uri tree change hands, the previous owner SHOULD
   take care to communicate existing media types to the new owner, and
   the new owner SHOULD take care to avoid collisions. Previous owners
   MAY publish a transition plan to a new domain, if doing so is judged
   to cause minimal disruption.

References

   [RFC1591]  Postel, J., "Domain Name System Structure and Delegation",
              RFC 1591, March 1994.

   [RFC2048]  Freed, N., Klensin, J. and J. Postel, "Multipurpose
              Internet Mail Extensions (MIME) Part Four: Registration
              Procedures", BCP 13, RFC 2048, November 1996.

   [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.

   [RFC3023]  Murata, M., St. Laurent, S. and D. Kohn, "XML Media
              Types", RFC 3023, January 2001.


Authors' Addresses

   Mark Nottingham
   BEA Systems


   Mark Baker

Appendix A. Acknowledgements

   The following people gave input and feedback during the creation of
   this document; Graham Klyne, Don Box, David Orchard, John Kemp and
   Ted Hardie. All errors are the responsibility of the authors.




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