The Atom "deleted-entry" Element
draft-snell-atompub-tombstones-05.txt

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Abstract

This specification adds mechanisms to the Atom Syndication Format which Atom Feed publishers can use to explicitly identify Atom entries that have been removed from an Atom feed.

Table of Contents

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

1.  Introduction

This specification adds a new element to the Atom Syndication Format [RFC4287] (Nottingham, M., Ed. and R. Sayre, Ed., “The Atom Syndication Format,” December 2005.) that can be used to explicitly indicate that specific entries have been removed from a feed.

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] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.)

This specification uses XML Namespaces [W3C.REC‑xml‑names‑19990114] (Hollander, D., Layman, A., and T. Bray, “Namespaces in XML,” January 1999.) to uniquely identify XML element names. It uses the following namespace prefix for the indicated namespace URI;

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

3.  The at:deleted-entry element

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

  deletedEntry = element at:deleted-entry {
    atomCommonAttributes,
    attribute ref { atomUri },
    attribute when { atomDateConstruct },
    ( element at:by { atomPersonConstruct}?,
    & element at:comment {atomTextConstruct}?,
    & extensionElement* )
  }

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

The at:deleted-entry element MUST contain a when attribute whose value is an [RFC3339] (Klyne, G., Ed. and C. Newman, “Date and Time on the Internet: Timestamps,” July 2002.) "date-time" specifying the instant the entry was removed from the feed. 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 at:deleted-entry element MAY contain one at:by element used to identify the entity that removed the entry from the feed. The at:by element is an Atom Person Construct as defined by Section 3.2 of [RFC4287] (Nottingham, M., Ed. and R. Sayre, Ed., “The Atom Syndication Format,” December 2005.).

The at:deleted-entry element MAY contain one at:comment element whose value provides additional, language-sensitive information about the deletion operation. The atom:comment element is an Atom Text Construct as defined by Section 3.1 of [RFC4287] (Nottingham, M., Ed. and R. Sayre, Ed., “The Atom Syndication Format,” December 2005.).

An Atom feed MAY contain any number of at:deleted-entry elements, but MUST NOT contain more than one with the same combination of ref and when attribute values.

  <feed xmlns="http://www.w3.org/2005/Atom"
        xmlns:at="http://purl.org/atompub/tombstones/1.0">
     ...
     <!-- Minimal deleted-entry -->
     <at:deleted-entry
       ref="tag:example.org,2005:/entries/1"
       when="2005-11-29T12:11:12Z"/>

     <!-- Extended deleted-entry -->
     <at:deleted-entry
       ref="tag:example.org,2005:/entries/2"
       when="2005-11-29T12:11:12Z">
       <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 at:deleted-entry elements sharing the same atom:id value. Atom processors SHOULD ignore any at: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 at:deleted-entry element's when value.

Elements and attributes from other XML vocabularies MAY be used within an at:deleted-entry element following the same model defined by Section 6 of [RFC4287] (Nottingham, M., Ed. and R. Sayre, Ed., “The Atom Syndication Format,” December 2005.). Processors encountering such markup MUST NOT stop processing or signal an error. It might be the case that the Processor is able to process the foreign markup correctly and does so. When unknown markup is encountered as a child of at:deleted-entry, Processors MAY bypass the markup and any textual content and MUST NOT change their behavior as a result of the markup's presence.

4.  Security Considerations

As specified in [RFC4287] (Nottingham, M., Ed. and R. Sayre, Ed., “The Atom Syndication Format,” December 2005.), 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.

5.  IANA Considerations

No IANA actions are required by this document.

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. Normative References

Author's Address

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