Network Working Group J. Snell
Internet-Draft January 4, 2008
Updates: 4287 (if approved)
Intended status: Standards Track
Expires: July 7, 2008
Atom Syndication Format Tombstones
draft-snell-atompub-tombstones-04.txt
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Copyright Notice
Copyright (C) The IETF Trust (2008).
Abstract
This specification adds mechanisms to the Atom Syndication Format
which Atom Feed publishers can use to 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 at:deleted-entry element . . . . . . . . . . . . . . . . . 3
4. The Trash Link Relation . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
6.1. The Link Relation Registration "Trash" . . . . . . . . . . 6
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
8. Normative References . . . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 6
Intellectual Property and Copyright Statements . . . . . . . . . . 8
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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;
"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 the 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 atom:id of the entry that has been removed.
The at:deleted-entry element MAY contain a 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 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].
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The at:deleted-entry element MAY contain one at: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 at:deleted-entry
elements, but MUST NOT contain more than one with the same ref
attribute value.
...
John Doejdoe@example.orgRemoved comment spam
...
An Atom feed MAY contain atom:entry elements and at:deleted-entry
elements sharing the same atom:id value. Atom processors MUST 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. If the at:
deleted-entry element does not contain a when element, the at:
deleted-entry sharing the same atom:id as an entry MUST be ignored.
4. The Trash Link Relation
This specification registers a new "trash" link relation to the Atom
Registry of Link Relations defined in Section 7.1 of [RFC4287]. When
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. If the linked
resource is an Atom Feed Document, each of the entries in that feed
will contain copies of the atom:entry elements removed from the feed
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containing the trash links.
For example,
...
...
A single linked trash resource may list entries deleted from multiple
feed documents. In such cases, each entry in the trash resource
SHOULD reference the feed from which the entry was removed. For
instance, if the trash resource is an Atom Feed Document, each entry
would contain an atom:source element identifying the feed the entry
was deleted from.
Linked "trash" resources are orthogonal to the at:deleted-entry
element and are intended to provide servers with a way of allowing
clients to recover deleted entries. For instance, the entries in a
feed may be managed by two separate authors, one of whom may delete
an entry that the other author wishes to later recover. If a trash
feed is provided, the second author can look for a copy of the
deleted entry there.
While it will be common for servers to provide only a single trash
resource per feed, or to have multiple feeds share a single trash
resource, it is possible for a single feed to contain multiple trash
links. The relationship between multiple trash links is undefined.
Individual entries deleted from the feed containing the linked trash
resources MAY appear in any, all or none of the linked trash
resources. It is up to the server implementation to decide whether
to provide a trash resource and whether or not to add deleted entries
to those resources.
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
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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).
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,
.
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Author's Address
James M Snell
Phone:
Email: jasnell@gmail.com
URI: http://snellspace.com
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