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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 RFC 6721

Network Working Group                                           J. Snell
Internet-Draft                                           January 2, 2008
Intended status: Standards Track
Expires: July 5, 2008


                   Atom Syndication Format Tombstones
                 draft-snell-atompub-tombstones-03.txt

Status of this Memo

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   This Internet-Draft will expire on July 5, 2008.

Copyright Notice

   Copyright (C) The IETF Trust (2008).

Abstract

   This specification defines mechanisms by which Atom Feed publishers
   can 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 atom:deleted-entry element  . . . . . . . . . . . . . . . . 3
   4.  The Trash Link Relation . . . . . . . . . . . . . . . . . . . . 4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
     6.1.  The Link Relation Registration "Trash"  . . . . . . . . . . 5
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 6
   8.  Normative References  . . . . . . . . . . . . . . . . . . . . . 6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 6
   Intellectual Property and Copyright Statements  . . . . . . . . . . 7






































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1.  Introduction

   This specification adds a new element to the Atom Syndication Format
   [RFC4287] that can be used to explicitly indicate that specific Atom
   entries have been removed from an Atom Feed Document.


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 atom:deleted-entry element

   The atom: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 atom:deleted-entry {
       atomCommonAttributes,
       ( & atomID,
         & element atom:when { atomDateConstruct }?,
         & element atom:by { atomPersonConstruct}?,
         & element atom:comment {atomTextConstruct}?,
         & extensionElement* )
     }

   The atom:deleted-entry element MUST contain one atom:id element whose
   value specifies the atom:id of the entry that has been removed.

   The atom:deleted-entry element MAY contain one atom:when element
   whose value is an [RFC3339] "date-time" specifying the instant the
   entry 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 atom:deleted-entry element MAY contain one atom:by element used
   to identify the entity that removed the entry from the feed.  The
   atom:by element is an Atom Person Construct as defined by Section 3.2
   of [RFC4287].




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   The atom:deleted-entry element MAY contain one atom:comment element
   whose value provides additional information about the deletion
   operation.  The atom:comment element is an Atom Text Construct as
   defined by Section 3.1 of [RFC4287].

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

     <feed xmlns="http://www.w3.org/2005/Atom">
        ...
        <!-- Minimal deleted-entry -->
        <deleted-entry>
          <id>tag:example.org,2005:/entries/1</id>
        </deleted-entry>

        <!-- Extended deleted-entry -->
        <deleted-entry>
          <id>tag:example.org,2005:/entries/2</id>
          <when>2005-11-29T12:11:12Z</when>
          <by>
            <name>John Doe</name>
            <email>jdoe@example.org</email>
          </by>
          <comment>Removed comment spam</comment>
        </deleted-entry>
        ...
     </feed>

   An Atom feed MAY contain atom:entry elements and atom:deleted-entry
   elements sharing the same atom:id value.  Atom processors MUST ignore
   any atom:deleted-entry elements sharing an atom:id value with an
   atom:entry whose atom:updated element specifies a date and time more
   recent than the atom:deleted-entry element's atom:when value.  If the
   atom:deleted-entry element does not contain an atom:when element, the
   atom:deleted-entry sharing the same atom:id as an entry MUST be
   ignored.


4.  The Trash Link Relation

   When an entry is deleted from one feed, a server can choose to move
   that entry into another Feed document whose member entries consist
   entirely of deleted entries.  Such "trash" feeds are similar in
   nature to desktop operating system trash folders that are used to
   collect, and potentially recover items that have been deleted.

   This specification registers a new "trash" link relation to the Atom
   Registry of Link Relations defined in Section 7.1 of [RFC4287].  When



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   appearing on atom:link elements within either the atom:feed or atom:
   source elements, The "trash" rel attribute value signifies that the
   IRI in the value of href attribute identifies a resource listing
   entries that have been deleted from the Feed document.

   For example,

    <feed xmlns="http://www.w3.org/2005/Atom">
      ...
      <link rel="trash" type="application/atom+xml" href="trash.xml" />
      <link rel="trash" type="application/xhtml+xml" href="trash.xml" />
      ...
    </feed>


5.  Security Considerations

   As specified in [RFC4287], Atom processors should be aware of the
   potential for spoofing attacks where an attacker publishes atom:entry
   or atom:deleted-entry elements using the same atom:id values as
   entries from other Atom feeds.  An attacker may attempt to trick an
   application into believing that a given entry has either been removed
   from or added to a feed.  To mitigate this issue, Atom processors are
   advised to ignore atom: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.


6.  IANA Considerations

6.1.  The Link Relation Registration "Trash"

   Attribute Value:  trash
   Description:  An IRI of a resource listing deleted resources.  When
      appearing within an atom:feed or atom:source elements, signifies
      that the IRI in the value of the href attribute identifies a
      resource listing entries that have been deleted from the Feed
      document.
   Expected display characteristics:  Undefined; this relation can be
      used for background processing or to provide extended
      functionality without displaying its value.
   Security considerations:  Automated agents should take care when this
      relation crosses administrative domains (e.g., the URI has a
      different authority than the current document).






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7.  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.


8.  Normative References

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

   [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@gmail.com
   URI:   http://snellspace.com


















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Full Copyright Statement

   Copyright (C) The IETF Trust (2008).

   This document is subject to the rights, licenses and restrictions
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   retain all their rights.

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Acknowledgment

   Funding for the RFC Editor function is provided by the IETF
   Administrative Support Activity (IASA).





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