Network Working Group A. Brown
Internet-Draft G. Clemm
Intended status: Informational IBM
Expires: July 16, 2010 J. Reschke, Ed.
greenbytes
January 12, 2010
Link Relations for Simple Version Navigation
draft-brown-versioning-link-relations-06
Abstract
This specification defines Atom link relations for navigation between
a resource and its versions.
Editorial Note (To be removed by RFC Editor before publication)
Please send comments to the Atom Syntax mailing list
(<http://www.imc.org/atom-syntax/>).
Note that although discussion takes place on the Atompub working
group's mailing list, this is not a working group document.
XML versions, latest edits and the issues list for this document are
available from <http://greenbytes.de/tech/
webdav/#draft-brown-versioning-link-relations>.
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This Internet-Draft will expire on July 16, 2010.
Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Link Relations . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. version-history . . . . . . . . . . . . . . . . . . . . . 5
3.2. latest-version . . . . . . . . . . . . . . . . . . . . . . 5
3.3. working-copy . . . . . . . . . . . . . . . . . . . . . . . 5
3.4. working-copy-of . . . . . . . . . . . . . . . . . . . . . 5
3.5. predecessor-version . . . . . . . . . . . . . . . . . . . 5
3.6. successor-version . . . . . . . . . . . . . . . . . . . . 6
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
4.1. 'version-history' Link Relation Registration . . . . . . . 6
4.2. 'latest-version' Link Relation Registration . . . . . . . 6
4.3. 'working-copy' Link Relation Registration . . . . . . . . 6
4.4. 'working-copy-of' Link Relation Registration . . . . . . . 7
4.5. 'predecessor-version' Link Relation Registration . . . . . 7
4.6. 'successor-version' Link Relation Registration . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Normative References . . . . . . . . . . . . . . . . . . . 8
7.2. Informative References . . . . . . . . . . . . . . . . . . 8
Appendix A. Relationship to Java Content Repository (JCR) and
WebDAV . . . . . . . . . . . . . . . . . . . . . . . 9
A.1. Example: Use of Link Relations in HTTP Link Header . . . . 10
Appendix B. Change Log (to be removed by RFC Editor before
publication) . . . . . . . . . . . . . . . . . . . . 12
B.1. Since draft-brown-link-relations-00 . . . . . . . . . . . 12
B.2. Since draft-brown-link-relations-01 . . . . . . . . . . . 12
B.3. Since draft-brown-link-relations-02 . . . . . . . . . . . 12
B.4. Since draft-brown-link-relations-03 . . . . . . . . . . . 12
B.5. Since draft-brown-link-relations-04 . . . . . . . . . . . 12
B.6. Since draft-brown-link-relations-05 . . . . . . . . . . . 12
Appendix C. Resolved issues (to be removed by RFC Editor
before publication) . . . . . . . . . . . . . . . . . 12
C.1. edit . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
C.2. expose-urls . . . . . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
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1. Introduction
This specification defines link relations that may be used on a
resource that exists in a system that supports versioning to navigate
among the different resources available, such as past versions.
These link relations are used in the AtomPub ([RFC5023]) bindings of
the "Content Management Interoperability Services" (CMIS). See
Section 3.4.3.1 of [CMIS] for further information.
2. Terminology
Versioned Resource
When a resource is put under version control, it becomes a
"versioned resource". Many servers protect versioned resources
from modifications by considering them "checked in", and by
requiring a "checkout" operation before modification, and a
"checkin" operation to get back to the "checked-in" state. Other
servers allow modification, in which case the checkout/checkin
operation may happen implicitly.
Version History
A "version history" resource is a resource that contains all the
versions of a particular versioned resource.
Predecessor, Successor
When a versioned resource is checked out and then subsequently
checked in, the version that was checked out becomes a
"predecessor" of the version created by the checkin. A client can
specify multiple predecessors for a new version if the new version
is logically a merge of those predecessors. The inverse of the
predecessor relation is the "successor" relation. Therefore, if X
is a predecessor of Y, then Y is a successor of X.
Working Copy
A "working copy" is a resource at a server-defined URL that can be
used to create a new version of a versioned resource.
Checkout
A "checkout" is an operation on a versioned resource that creates
a working copy, or changes the versioned resource to be a working-
copy as well ("in-place versioning").
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Checkin
A "checkin" is an operation on a working copy that creates a new
version of its corresponding versioned resource.
Note: the operations for putting a resource under version control,
and for checking in and checking out depend on the protocol in use
and are beyond the scope of this document; see [CMIS], [RFC3253]
and [JSR-283] for examples.
3. Link Relations
The following link relations are defined:
3.1. version-history
When included on a versioned resource, this link points to a resource
containing the version history for this resource.
3.2. latest-version
When included on a versioned resource, this link points to a resource
containing the latest (e.g., current) version.
The latest version is defined by the system. For linear versioning
systems, this is probably the latest version by timestamp. For
systems that support branching, there will be multiple latest
versions, one for each branch in the version history.
Some systems may allow multiple of these link relations.
3.3. working-copy
When included on a versioned resource, this link points to a working
copy for this resource.
Some systems may allow multiple of these link relations.
3.4. working-copy-of
When included on a working copy, this link points to the versioned
resource from which this working copy was obtained.
3.5. predecessor-version
When included on a versioned resource, this link points to a resource
containing the predecessor version in the version history.
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Some systems may allow multiple of these link relations in the case
of a multiple branches merging.
3.6. successor-version
When included on a versioned resource, this link points to a resource
containing the successor version in the version history.
Some systems may allow multiple of these link relations in order to
support branching.
4. IANA Considerations
The link relations below are to be registered by IANA per Section 7.1
of [RFC4287]:
4.1. 'version-history' Link Relation Registration
Attribute Value: version-history
Description: See Section 3.1.
Expected display characteristics: Undefined; this relation can be
used for background processing or to provide extended
functionality without displaying its value.
Security considerations: See Section 5.
4.2. 'latest-version' Link Relation Registration
Attribute Value: latest-version
Description: See Section 3.2.
Expected display characteristics: Undefined; this relation can be
used for background processing or to provide extended
functionality without displaying its value.
Security considerations: See Section 5.
4.3. 'working-copy' Link Relation Registration
Attribute Value: working-copy
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Description: See Section 3.3.
Expected display characteristics: Undefined; this relation can be
used for background processing or to provide extended
functionality without displaying its value.
Security considerations: See Section 5.
4.4. 'working-copy-of' Link Relation Registration
Attribute Value: working-copy-of
Description: See Section 3.4.
Expected display characteristics: Undefined; this relation can be
used for background processing or to provide extended
functionality without displaying its value.
Security considerations: See Section 5.
4.5. 'predecessor-version' Link Relation Registration
Attribute Value: predecessor-version
Description: See Section 3.5.
Expected display characteristics: Undefined; this relation can be
used for background processing or to provide extended
functionality without displaying its value.
Security considerations: See Section 5.
4.6. 'successor-version' Link Relation Registration
Attribute Value: successor-version
Description: See Section 3.6.
Expected display characteristics: Undefined; this relation can be
used for background processing or to provide extended
functionality without displaying its value.
Security considerations: See Section 5.
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5. Security Considerations
Automated agents should take care when these relations cross
administrative domains (e.g., the URI has a different authority than
the current document). Such agents should also take care to detect
circular references.
Care should be applied when versioned resources are subject to
differing access policies. In this case, exposing links may leak
information even if the linked resource itself is properly secured.
In particular, the syntax of the link URI/IRI could expose sensitive
information (see Section 16.2 of [RFC3253] for a similar
consideration in WebDAV Versioning). Note that this applies to
exposing link metadata in general, not only to links related to
versioning.
6. Acknowledgments
Thanks to the members of Content Management Interoperability Services
(CMIS) Technical Committee (TC) at OASIS for the initial proposal,
and to Jan Algermissen for feedback during IETF review.
7. References
7.1. Normative References
[RFC4287] Nottingham, M. and R. Sayre, "The Atom Syndication
Format", RFC 4287, December 2005.
7.2. Informative References
[CMIS] Brown, A., Gur-Esh, E., McVeigh, R., and F. Muller,
"Content Management Interoperability Services (CMIS)
Version 1.0", OASIS CMIS v1.0 Committee Draft 04,
September 2009, <http://docs.oasis-open.org/cmis/CMIS/
v1.0/cd04/cmis-spec-v1.0.html>.
[JSR-283] Day Software, Nuescheler, D., and P. Piegaze, "Content
Repository API for Java(tm) Technology Specification",
Java Specification Request 283, August 2009,
<http://www.day.com/specs/jcr/2.0/>.
[RFC3253] Clemm, G., Amsden, J., Ellison, T., Kaler, C., and J.
Whitehead, "Versioning Extensions to WebDAV (Web
Distributed Authoring and Versioning)", RFC 3253,
March 2002.
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[RFC5023] Gregorio, J. and B. de hOra, "The Atom Publishing
Protocol", RFC 5023, October 2007.
[draft-nottingham-http-link-header]
Nottingham, M., "Web Linking",
draft-nottingham-http-link-header-06 (work in progress),
July 2009.
Appendix A. Relationship to Java Content Repository (JCR) and WebDAV
The link relations defined in Section 3 correspond to various
properties used in WebDAV Versioning [RFC3253] and JCR [JSR-283]:
version-history
WebDAV: the resource identified by the DAV:version-history
property ([RFC3253], Sections 5.2.1 and 5.3.1).
JCR: the node identified by jcr:versionHistory property
([JSR-283], Section 3.13.2.4) for versionable nodes, the parent
folder for version nodes.
latest-version
WebDAV: for version-controlled resources, DAV:checked-in
([RFC3253], Section 3.2.1) or DAV:checked-out ([RFC3253], Section
3.3.1), depending on checkin state. For version resources, a
successor version that itself does not have any successors.
JCR: the version node identified by the jcr:baseVersion property
([JSR-283], Section 3.13.2.5) for versionable nodes; for version
nodes, a successor version that itself does not have any
successors.
working-copy
WebDAV: for version-controlled resources that are checked-out in
place: the resource itself. For version resources: each resource
identified by a member of the DAV:checkout-set property (see
[RFC3253], Section 3.4.3).
JCR: for checked-out versionable nodes: the node itself.
working-copy-of
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WebDAV: the resource identified by the the DAV:checked-out
property (see [RFC3253], Section 3.3.1).
JCR: for checked-out versionable nodes: the node identified by the
jcr:baseVersion property ([JSR-283], Section 3.13.12.5).
predecessor-version
WebDAV: each resource identified by a member of DAV:predecessor-
set ([RFC3253], Sections 3.3.2 and 3.4.1).
JCR: each node identified by a member of jcr:predecessors
([JSR-283], Section 3.13.3.3).
successor-version
WebDAV: each resource identified by a member of DAV:successor-set
([RFC3253], Section 3.4.2).
JCR: each node identified by a member of jcr:successors
([JSR-283], Section 3.13.3.4).
A.1. Example: Use of Link Relations in HTTP Link Header
The "Web Linking" specification ([draft-nottingham-http-link-header])
generalizes Atom link relations, and also re-introduces the HTTP
"Link" header as a way to expose link relations in HTTP responses.
This will make it possible to expose version links independently from
a specific vocabulary, be it the Atom Feed Format ([RFC4287]) or
WebDAV properties ([RFC3253]).
For instance, a response to an VERSION-CONTROL request ([RFC3253],
Section 3.5) could expose newly created version-history and
checked-in version as link relations:
>> Request:
VERSION-CONTROL /docs/test.txt HTTP/1.1
Host: example.net
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>> Response:
HTTP/1.1 204 No Content
Link: </system/v/84345634/1>; rel=latest-version;
anchor=</docs/test.txt>
Link: </system/vh/84345634>; rel=version-history;
anchor=</docs/test.txt>
(Note that in this case, the anchor parameter is used, as the
response to a VERSION-CONTROL request is not a representation of the
resource at the Request-URI)
A subsequent HEAD request on that resource could expose the version-
history and latest-version relations as well:
>> Request:
HEAD /docs/test.txt HTTP/1.1
Host: example.net
>> Response:
HTTP/1.1 200 OK
Content-Type: text/plain; charset=UTF-8
Content-Length: 12345
Link: </system/v/84345634/1>; rel=latest-version
Link: </system/vh/84345634>; rel=version-history
After creating more versions, following the latest-version would then
expose predecessors of a version:
>> Request:
HEAD /system/v/84345634/3 HTTP/1.1
Host: example.net
>> Response:
HTTP/1.1 200 OK
Content-Type: text/plain; charset=UTF-8
Content-Length: 12323
Link: </system/v/84345634/2>; rel=predecessor-version
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Appendix B. Change Log (to be removed by RFC Editor before publication)
B.1. Since draft-brown-link-relations-00
Added Geoff Clemm as author.
Renamed link relation "all-versions" to "version-history". Fixed
description of "working-resource" relation to state that it appears
on a version resource.
B.2. Since draft-brown-link-relations-01
Rewrite terminology and link relations using simpler definitions that
can reflect versioning approaches different from WebDAV.
Add JCR/WebDAV property table. And reference to Web Linking draft
(for now informative) and examples showing use of the Link header.
B.3. Since draft-brown-link-relations-02
Add and resolve issue "iana".
B.4. Since draft-brown-link-relations-03
Fix typo ("working-resource" instead of "working-copy"). Add and
resolve issues "checked-out", "cmis" and "working-copy-of".
B.5. Since draft-brown-link-relations-04
Close issue "working-copy-of", which was really fixed in -04.
B.6. Since draft-brown-link-relations-05
Fix VERSION-CONTROL example to return 204 (there's no response body).
Fix country names in contact information. Add and resolve issue
"expose-urls".
Appendix C. Resolved issues (to be removed by RFC Editor before
publication)
Issues that were either rejected or resolved in this version of this
document.
C.1. edit
Type: edit
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julian.reschke@greenbytes.de (2009-11-19): Umbrella issue for
editorial fixes/enhancements.
C.2. expose-urls
In Section 5:
Type: change
ekr@networkresonance.com (2010-01-03): In general this mechanism
seems sound but I'm not sure that the security considerations are
entirely adequate. This mechanism lets you learn information about
other versions of a resource even if you potentially don't have
permission to view them directly. Consider a limiting case where
each version of the resource had a name that contained the change set
for that resource. E.g.,
http://example.com/versions/filename/_@line_50_+_FOO;@line_60_+_BAR/;
In this case, seeing other parts of the version tree leaks
information about those versions. I don't think that this is a
problem for the draft, but it might be useful to mention that this
feature has implications for name construction.
Resolution (2010-01-06): Add that consideration.
Authors' Addresses
Al Brown
IBM
3565 Harbor Blvd
Costa Mesa, California 92626
USA
Email: albertcbrown@us.ibm.com
Geoffrey Clemm
IBM
20 Maguire Road
Lexington, MA 02421
USA
Email: geoffrey.clemm@us.ibm.com
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Julian F. Reschke (editor)
greenbytes GmbH
Hafenweg 16
Muenster, NW 48155
Germany
Email: julian.reschke@greenbytes.de
URI: http://greenbytes.de/tech/webdav/
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