Network Working Group J. Snell
Internet-Draft February 27, 2006
Expires: August 31, 2006
Atom Syndication Format Revision Tracking
draft-snell-atompub-revision-00.txt
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Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
This specification defines metadata extensions for use with the Atom
Syndication Format to track revisions of entries.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 3
3. The 'revision' element . . . . . . . . . . . . . . . . . . . . 3
4. The 'host' Element . . . . . . . . . . . . . . . . . . . . . . 5
5. The 'comment' Element . . . . . . . . . . . . . . . . . . . . 6
6. The 'deleted-entry' element . . . . . . . . . . . . . . . . . 7
7. The 'history' Link Relation . . . . . . . . . . . . . . . . . 8
8. The 'diff' Link Relation . . . . . . . . . . . . . . . . . . . 9
9. The 'initial-revision' Link Relation . . . . . . . . . . . . . 10
10. The 'current-revision' Link Relation . . . . . . . . . . . . . 10
11. The 'this-revision' Link Relation . . . . . . . . . . . . . . 10
12. The 'prior-revision' Link Relation . . . . . . . . . . . . . . 11
13. The 'next-revision' Link Relation . . . . . . . . . . . . . . 11
14. Security Considerations . . . . . . . . . . . . . . . . . . . 12
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
16. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 15
Intellectual Property and Copyright Statements . . . . . . . . . . 16
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1. Introduction
This specification defines metadata extensions for use with the Atom
Syndication Format [RFC4287] to track revisions of entries. The
extensions include versioning of entries, links to change summaries
and histories, and indicators as to the relative importance, or
significance of the revision.
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}
"ar": "http://purl.org/atompub/revision/1.0"
3. The 'revision' element
The 'revision' element MAY appear as a child of an atom:entry element
to identify a "revision number" for the entry.
revision = element ar:revision {
atomCommonAttributes,
attribute number { text },
attribute scheme { atomIRI }?,
attribute label { text }?,
attribute when { date-time }?,
attribute initial { 'yes' | 'no' }?,
attribute final { 'yes' | 'no' }?,
attribute significant { 'yes' | 'no' }?,
( atomTextConstruct )
}
The 'revision' element is an extension of the Atom Text Construct
that is used to identify a "revision number" for an entry. The
revision element MUST contain a 'number' attribute whose value
identifies the revision number of the entry. The text value of the
element MAY be used to provide a summary of the revision. Within the
number attribute, escaped versions of characters such as "&" and ">"
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represent those characters, not markup.
The 'scheme' attribute MAY be used to provide an IRI identifying the
scheme used to produce the revision number specified by the 'number'
attribute. If the scheme attribute is not specified, the value of
the 'number' attribute MUST be a non-negative numeric value.
The 'label' attribute MAY be used to associate a simple human
readable text label with the revision. Within the value, escaped
versions of characters such as "&" and ">" represent those
characters, not markup.
The 'when' attribute MAY be used to provide an RFC3339 date-time
specifying the date and time that the revision was performed. 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 'initial' attribute indicates whether or not this revision
represents the initial version of an entry. The value is either
"yes" or "no". When missing, the value is considered to be "no".
The 'final' attribute indicates whether or not this revision
represents the final version of an entry. The value is either "yes"
or "no". Feed publishers SHOULD NOT continue to update atom:entry's
that have been marked as "final" revisions. Atom processors MAY
ignore atom:entry elements with revision element values and atom:
updated values greater than those specified in a "final" revision.
When missing, the value is considered to be "no".
The 'significant' attribute indicates whether or not the revision
should be considered to be "significant" or not. The value is either
"yes" or "no". Atom processors MAY choose to process or present
significant revisions differently than non-significant revisions.
When missing, the value is considered to be "no".
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For example,
<feed xmlns="http://www.w3.org/2005/Atom">
...
<entry>
...
<ar:revision
number="0.1"
when="2006-02-21T00:00:00Z"
initial="yes"
final="no"
significant="yes"
type="text">
Fixed typographical and factual errors
</ar:revision>
...
</entry>
</feed>
An Atom entry is a revision of a prior entry only if the two entries
share the same atom:id value and the revision number attribute and
atom:updated element values are both greater than the previous
version of the entry.
4. The 'host' Element
Atom Person Constructs contained within an atom entry MAY contain a
'host' element whose value is either the IP Address or Domain host
name from which the person created or modified the entry.
Within value of the 'host' element, the escaped versions of
characters such as "&" and ">" represent those characters, not
markup.
host = element ar:host { text }
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For example,
<feed xmlns="http://www.w3.org/2005/Atom">
...
<entry>
...
<author>
<name>James</name>
<ar:host>192.168.1.106</ar:host>
</author>
...
</entry>
</feed>
5. The 'comment' Element
Atom entry and feed elements MAY contain zero or more 'comment'
elements that provide the equivalent to editorial notes.
comment = element ar:comment {
atomCommonAttributes,
(atomAuthor?,
atomUpdated,
atomSummary,
undefinedContent)
}
The 'comment' element SHOULD contain an atom:author element
identifying the person or entity that created the comment.
The 'comment' element MUST contain one atom:updated element that
specifies the date and time that the comment was created and added to
the entry or feed.
The 'comment' element MUST contain one atom:summary element that
contains containing the text of the comment.
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For example,
<feed xmlns="http://www.w3.org/2005/Atom">
...
<entry>
...
<ar:comment>
<author><name>James</name></author>
<updated>2006-02-21T00:00:00Z</updated>
<summary>
We still need to fix the factual errors in this entry
</summary>
</ar:comment>
...
</entry>
</feed>
6. 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,
& revision?,
& when,
& by?,
& undefinedContent )
}
when = element at:when { atomDateConstruct }
by = element at:by { atomPersonConstruct }
The 'deleted-entry' element MUST contain one 'atom:id' element whose
value specifies the atom:id of the deleted entry.
The 'deleted-entry' MAY contain one revision element.
One 'when' element MUST be provided specifying the instant the entry
was deleted. The 'when' element is an Atom Date Construct as defined
by [RFC4287].
One 'by' element MAY by provided to identify the person or entity
that removed the entry from the feed. The 'by' element is an Atom
Person Construct as defined by [RFC4287].
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Atom Feed Documents MAY contain any number of 'deleted-entry'
elements.
<feed xmlns="http://www.w3.org/2005/Atom">
...
<ar:deleted-entry>
<id>tag:example.org,2005:/entries/1</id>
<ar:revision
number="3">Removed comment spam</ar:revision>
<ar:when>2005-11-29T12:12:12Z</ar:when>
<ar:by>
<name>John Doe</name>
<email>jdoe@example.org</email>
<ar:host>192.168.1.106</ar:host>
</ar:by>
</ar: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.
7. The 'history' Link Relation
Atom entry elements MAY contain an atom:link element with a rel
attribute value of 'history' whose href attribute identifies a
resource describing the revision history of the entry. If the
history link points to an Atom Feed Document, the referenced feed
MUST contain one or more atom:entry or 'deleted-entry' elements, each
of which represents one revision of the entry. The entry and
deleted-entry elements MUST have the same atom:id value and MUST have
different 'revision', atom:updated or when values.
<feed xmlns="http://www.w3.org/2005/Atom">
...
<entry>
...
<link rel="history" type="application/atom+xml"
href="http://example.org/entry/1/history" />
...
</entry>
</feed>
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An example History Feed
<feed xmlns="http://www.w3.org/2005/Atom">
...
<ar:deleted-entry>
<id>tag:example.org,2006:entries/1</id>
<ar:revision
number="3"
final="yes"
significant="yes" />
<ar:when>2006-02-27T00:00:00Z</ar:when>
</ar:deleted-entry>
<entry>
<id>tag:example.org,2006:entries/1</id>
<updated>2006-02-26T00:00:00Z</updated>
<ar:revision
number="2"
significant="no">Fixed typos</ar:revision>
...
</entry>
<entry>
<id>tag:example.org,2006:entries/1</id>
<updated>2006-02-25T00:00:00Z</updated>
<ar:revision
number="1"
initial="yes"
significant="yes" />
...
</entry>
</feed>
8. The 'diff' Link Relation
Atom entry elements MAY contain an atom:link element with a rel
attribute value of 'diff' whose href attribute identifies a resource
describing the deltas between this revision of the entry and the
previous revision.
<feed xmlns="http://www.w3.org/2005/Atom">
...
<entry>
...
<link rel="diff"
href="http://example.org/entry/1/diff" />
...
</entry>
</feed>
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9. The 'initial-revision' Link Relation
Atom entry elements MAY contain an atom:link element with a rel
attribute value of 'initial-revision' whose href attribute specifies
the URI of an Atom Entry Document representing the initial version of
the entry.
<feed xmlns="http://www.w3.org/2005/Atom">
...
<entry>
...
<ar:revision number="0.2" />
<link rel="initial-revision" type="application/atom+xml"
href="http://example.org/entry/1?revision=0.1" />
...
</entry>
</feed>
10. The 'current-revision' Link Relation
Atom entry elements MAY contain an atom:link element with a rel
attribute value of 'current-revision' whose href attribute specifies
the URI of an Atom Entry Document representing the current version of
the entry.
<feed xmlns="http://www.w3.org/2005/Atom">
...
<entry>
...
<ar:revision number="0.2" />
<link rel="current-revision" type="application/atom+xml"
href="http://example.org/entry/1" />
...
</entry>
</feed>
11. The 'this-revision' Link Relation
Atom entry elements MAY contain an atom:link element with a rel
attribute value of 'this-revision' whose href attribute specifies the
URI of an Atom Entry Document representing the this version of the
entry.
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<feed xmlns="http://www.w3.org/2005/Atom">
...
<entry>
...
<ar:revision number="0.2" />
<link rel="this-revision" type="application/atom+xml"
href="http://example.org/entry/1?revision=0.2" />
...
</entry>
</feed>
12. The 'prior-revision' Link Relation
Atom entry elements MAY contain an atom:link element with a rel
attribute value of 'prior-revision' whose href attribute specifies
the URI of an Atom Entry Document representing the previous version
of the entry.
<feed xmlns="http://www.w3.org/2005/Atom">
...
<entry>
...
<ar:revision number="0.2" />
<link rel="prior-revision" type="application/atom+xml"
href="http://example.org/entry/1?revision=0.1" />
...
</entry>
</feed>
13. The 'next-revision' Link Relation
Atom entry elements MAY contain an atom:link element with a rel
attribute value of 'next-revision' whose href attribute specifies the
URI of an Atom Entry Document representing the subsequent version of
the entry.
<feed xmlns="http://www.w3.org/2005/Atom">
...
<entry>
...
<ar:revision number="0.2" />
<link rel="next-revision" type="application/atom+xml"
href="http://example.org/entry/1?revision=0.3" />
...
</entry>
</feed>
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14. Security Considerations
The extensions defined in this specification are subject to the same
security considerations as discussed in [RFC4287].
15. IANA Considerations
This specification defines seven new link relations for the IANA
Registry of Link Relations as defined by [RFC4287].
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Attribute Value: history
Description: identifies a resource describing the
revision history of an atom:entry
Display characteristics: None
Security considerations: Same as <xref target="RFC4287" />
Attribute Value: diff
Description: identifies a resource describing the
deltas between the current revision of
an atom:entry and its prior version.
Display characteristics: None
Security considerations: Same as <xref target="RFC4287" />
Attribute Value: initial-revision
Description: identifies an Atom Entry Document describing the
initial version of a resource
Display characteristics: None
Security considerations: Same as <xref target="RFC4287" />
Attribute Value: current-revision
Description: identifies an Atom Entry Document describing the
current version of a resource
Display characteristics: None
Security considerations: Same as <xref target="RFC4287" />
Attribute Value: this-revision
Description: identifies an Atom Entry Document describing the
version of the resource containing the this-revision
link.
Display characteristics: None
Security considerations: Same as <xref target="RFC4287" />
Attribute Value: prior-revision
Description: identifies an Atom Entry Document describing the
previous version of a resource
Display characteristics: None
Security considerations: Same as <xref target="RFC4287" />
Attribute Value: next-revision
Description: identifies an Atom Entry Document describing the
next version of a resource
Display characteristics: None
Security considerations: Same as <xref target="RFC4287" />
16. Acknowledgements
The author gratefully acknowledges the feedback from the members of
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the Atom Publishing Format and Protocol working group during the
development of this specification. Some of the language included in
this draft has been adapted directly from the Atom Syndication Format
[RFC4287] in order to maintain a stylistic and technical alignment to
that specification.
17. 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-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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