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Network Working Group                                           J. Snell
Internet-Draft                                         February 20, 2006
Expires: August 24, 2006


                   Atom Syndication Format Tombstones
                 draft-snell-atompub-tombstones-02.txt

Status of this Memo

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   This Internet-Draft will expire on August 24, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This specification defines mechanisms by which Atom Feed publishers
   may explicitly indicate that specific Atom Entries have been removed
   from an Atom feed.









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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Notational Conventions  . . . . . . . . . . . . . . . . . . . . 3
   3.  The 'deleted-entry' element . . . . . . . . . . . . . . . . . . 3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 5
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 6
   Intellectual Property and Copyright Statements  . . . . . . . . . . 7








































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1.  Introduction

   This specification defines mechanisms in the form of Atom Format
   [RFC4287] extensions that Atom Feed publishers can use to explicitly
   indicate that specific Atom Entries have been removed from a feed for
   any reason.


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;

   {Ed.  Note: this namespace MUST be changed to a proper IETF namespace
   scheme prior to publication}

    "at": "http://purl.org/atompub/tombstones/1.0"


3.  The 'deleted-entry' element

   The 'deleted-entry' element MAY appear as a child of atom:feed to
   represent an Atom Entry that has been removed from the feed.

     deletedEntry = element at:deleted-entry {
       atomCommonAttributes,
       ( & atomID,
         & when { atomDateConstruct },
         & by?,
         & comment?,
         & undefinedContent )
     }

     when = element at:when { atomDateConstruct }
     by = element at:by { atomPersonConstruct }
     comment = element at:comment { atomTextConstruct }


   The 'deleted-entry' element MUST contain one 'atom:id' element whose
   value specifies the atom:id of the deleted entry.

   The 'deleted-entry' element MUST contain one 'when' element whose
   value is an [RFC3339] "date-time" specifying the instant the entry



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   was deleted.  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 'deleted-entry' element MAY contain one 'by' element used to
   identify the entity that removed the entry from the feed.

   The 'deleted-entry' element MAY contain one 'comment' element whose
   value provides additional information about the deletion operation.
   The 'comment' element is Language-Sensitive as specified by
   [RFC4287].

   Atom Feed Documents MAY contain any number of 'deleted-entry'
   elements.

     <feed xmlns="http://www.w3.org/2005/Atom">
        ...
        <at:deleted-entry>
          <atom:id>tag:example.org,2005:/entries/1</atom:id>
          <at:when>2005-11-29T12:12:12Z</at:when>
          <at:by>
            <name>John Doe</name>
            <email>jdoe@example.org</email>
          </at:by>
          <at:comment>Removed comment spam</at:comment>
        </at:deleted-entry>
        <at:deleted-entry>
          <atom:id>tag:example.org,2005:/entries/2</atom:id>
          <at:when>2005-11-29T12:11:12Z</at:when>
          <at:by>
            <name>John Doe</name>
            <email>jdoe@example.org</email>
          </at:by>
          <at:comment>Removed comment spam</at:comment>
        </at:deleted-entry>
        ...
     </feed>

   An Atom feed MAY contain atom:entry elements and 'deleted-entry'
   elements sharing the same atom:id value.  Atom processors MUST ignore
   any 'deleted-entry' elements sharing an atom:id value with an atom:
   entry whose 'updated' element specifies a date and time more recent
   than the 'deleted-entry' element's 'when' value.


4.  Security Considerations

   As specified in [RFC4287], Atom processors should be aware of the



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   potential for spoofing attacks where an attacked publishes atom:entry
   elements with the same atom:id value of entries from other Atom
   feeds.  The same potential exists with the mechanisms defined here in
   that an attacker may attempt to spoof an application into believing
   that a given entry has been removed from a feed.  To mitigate this
   issue, Atom processors are advised to ignore 'deleted-entry' elements
   referencing entries that have not previously appeared within the
   containing Feed document and should take steps to verify the origin
   of the Atom feed before considering the entries to be removed.


5.  IANA Considerations

   There are no IANA considerations introduced by this specification.


6.  Acknowledgements

   The author gratefully acknowledges the feedback from the members of
   the Atom Publishing Format and Protocol working group during the
   development of this specification.

7.  References

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

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

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

   [W3C.REC-xml-infoset-20040204]
              Tobin, R. and J. Cowan, "XML Information Set (Second
              Edition)", W3C REC REC-xml-infoset-20040204,
              February 2004.

   [W3C.REC-xml-names-19990114]
              Hollander, D., Bray, T., and A. Layman, "Namespaces in
              XML", W3C REC REC-xml-names-19990114, January 1999.










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Author's Address

   James M Snell


   Phone:
   Email: jasnell@gmail.com
   URI:   http://snellspace.com











































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Intellectual Property Statement

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   ietf-ipr@ietf.org.


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Copyright Statement

   Copyright (C) The Internet Society (2006).  This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
   except as set forth therein, the authors retain all their rights.


Acknowledgment

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




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