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Network Working Group                                           J. Snell
Internet-Draft                                              May 12, 2010
Updates: 4287 (if approved)
Intended status: Informational
Expires: November 13, 2010


                          Atom Link Extensions
               draft-snell-atompub-link-extensions-03.txt

Abstract

   This specification adds additional attributes to the Atom Syndication
   Format link and content elements that may be used to express
   additional metadata about linked resources.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 13, 2010.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.




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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Notational Conventions  . . . . . . . . . . . . . . . . . . . . 3
   3.  The 'md5' attribute . . . . . . . . . . . . . . . . . . . . . . 3
   4.  The 'etag' attribute  . . . . . . . . . . . . . . . . . . . . . 3
   5.  The 'modified' attribute  . . . . . . . . . . . . . . . . . . . 4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 4
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
   8.  Normative References  . . . . . . . . . . . . . . . . . . . . . 4
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 5








































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1.  Introduction

   This specification adds additional attribute to the Atom Syndication
   Format [RFC4287] link and content elements that may be used to
   express additional metadata about linked resources.


2.  Notational Conventions

   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, [RFC2119]

   This specification uses XML Namespaces [W3C.REC-xml-names-19990114]
   to uniquely identify XML element names.  It uses the following
   namespace prefix for the indicated namespace URI;

    "atom": "http://www.w3.org/2005/Atom"


3.  The 'md5' attribute

   The 'md5' Attribute specifies a MD5 digest [RFC1864] of the resource
   identified by the atom:link/@href or atom:content/@src attributes.
   The value is represented as a sequence of 32 hexadecimal digits.  The
   'md5' attribute MAY appear as a child of the atom:link and atom:
   content elements.

     md5 = attribute md5 { md5-digest }
     md5-digest   = <hex of 128 bit MD5 digest as per RFC 1864>

   An example MD5 digest of an enclosed MP3 file:

     <atom:link rel="enclosure"
       href="http://example.org/media/myfile.mp3"
       md5="9e107d9d372bb6826bd81d3542a419d6" />

   The MD5 digest is computed based on the content of the entity-body as
   specified by Section 14.15 of [RFC2616].


4.  The 'etag' attribute

   The 'etag' Attribute specifies an Entity Tag [RFC2616] for the
   resource identified by the atom:link or atom:content element.  The
   'etag' attribute MAY appear as a child of the atom:link and atom:
   content elements.




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     etag = attribute le:etag { entity-tag }

     entity-tag = [ weak ] opaque-tag
     weak       = "W/"
     opaque-tag = quoted-string

   An example Entity Tag for an enclosed MP3 file:

     <atom:link rel="enclosure"
        href="http://example.org/media/myfile.mp3"
        etag="W/xyzzy" />


5.  The 'modified' attribute

   The 'modified' Attribute specifies the date and time when the
   resource identified by the atom:link or atom:content element was last
   modified.  The value MUST conform to the "date-time" production
   defined by [RFC3339].  An uppercase "T" character MUST be used to
   separate date and time, and an uppercase "Z" character MUST be
   present in the absence of a numeric time zone offset.  The 'modified'
   attribute MAY appear as a child of the atom:link and atom:content
   elements.

     modified = attribute modified { xsd:dateTime }

   An example last-modified attribute for an enclosed MP3 file:

     <atom:link rel="enclosure"
       href="http://example.org/media/myfile.mp3"
       modified="2010-12-12T12:12:12Z" />


6.  Security Considerations

   TBD


7.  IANA Considerations

   No IANA actions are required by this document.


8.  Normative References

   [RFC1864]  Myers, J. and M. Rose, "The Content-MD5 Header Field",
              RFC 1864, October 1995.




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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC3339]  Klyne, G., Ed. and C. Newman, "Date and Time on the
              Internet: Timestamps", RFC 3339, July 2002.

   [RFC4287]  Nottingham, M., Ed. and R. Sayre, Ed., "The Atom
              Syndication Format", RFC 4287, December 2005.

   [W3C.REC-xml-names-19990114]
              Hollander, D., Layman, A., and T. Bray, "Namespaces in
              XML", World Wide Web Consortium FirstEdition REC-xml-
              names-19990114, January 1999,
              <http://www.w3.org/TR/1999/REC-xml-names-19990114>.


Author's Address

   James M Snell


   Phone:
   Email: jasnell@us.ibm.com
   URI:   http://ibm.com























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