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rfc:rfc5829

Internet Engineering Task Force (IETF) A. Brown Request for Comments: 5829 G. Clemm Category: Informational IBM ISSN: 2070-1721 J. Reschke, Ed.

                                                            greenbytes
                                                            April 2010

Link Relation Types for Simple Version Navigation between Web Resources

Abstract

 This specification defines a set of link relation types that may be
 used on Web resources for navigation between a resource and other
 resources related to version control, such as past versions and
 working copies.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Not all documents
 approved by the IESG are a candidate for any level of Internet
 Standard; see Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc5829.

Copyright Notice

 Copyright (c) 2010 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Brown, et al. Informational [Page 1] RFC 5829 Version Navigation Link Relations April 2010

Table of Contents

 1. Introduction ....................................................3
 2. Terminology .....................................................3
 3. Link Relations ..................................................4
    3.1. 'version-history' ..........................................4
    3.2. 'latest-version' ...........................................4
    3.3. 'working-copy' .............................................4
    3.4. 'working-copy-of' ..........................................4
    3.5. 'predecessor-version' ......................................4
    3.6. 'successor-version' ........................................5
 4. IANA Considerations .............................................5
    4.1. 'version-history' Link Relation Registration ...............5
    4.2. 'latest-version' Link Relation Registration ................5
    4.3. 'working-copy' Link Relation Registration ..................5
    4.4. 'working-copy-of' Link Relation Registration ...............6
    4.5. 'predecessor-version' Link Relation Registration ...........6
    4.6. 'successor-version' Link Relation Registration .............6
 5. Security Considerations .........................................6
 6. Acknowledgments .................................................7
 7. References ......................................................7
    7.1. Normative References .......................................7
    7.2. Informative References .....................................7
 Appendix A.  Relationship to Java Content Repository (JCR) and
              WebDAV ................................................9
    A.1.  Example: Use of Link Relations in HTTP Link Header .......10

Brown, et al. Informational [Page 2] RFC 5829 Version Navigation Link Relations April 2010

1. Introduction

 This specification defines a set of link relation types that may be
 used on Web resources that exist in a system that supports versioning
 to navigate among the different resources available, such as past
 versions and working copies.
 These link relations are used in the AtomPub ([RFC5023]) bindings of
 the "Content Management Interoperability Services" (CMIS).  See
 Section 3.4.3.3 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").

Brown, et al. Informational [Page 3] RFC 5829 Version Navigation Link Relations April 2010

 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 more than one 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 more than one 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.

Brown, et al. Informational [Page 4] RFC 5829 Version Navigation Link Relations April 2010

 Some systems may allow more than one of these link relations in the
 case of 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 more than one of these link relations in order
 to support branching.

4. IANA Considerations

 The link relations below have been 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
 Description:  See Section 3.3.

Brown, et al. Informational [Page 5] RFC 5829 Version Navigation Link Relations April 2010

 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.

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.

Brown, et al. Informational [Page 6] RFC 5829 Version Navigation Link Relations April 2010

 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 target 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., Ed. and R. Sayre, Ed., "The Atom
             Syndication Format", RFC 4287, December 2005.

7.2. Informative References

 [CMIS]      Brown, A., Gur-Esh, E., McVeigh, R., and F.  Mueller,
             "Content Management Interoperability Services (CMIS)
             Version 1.0", OASIS Content Management Interoperability
             Services (CMIS) Version 1.0 Committee Specification 01,
             March 2010,  <http://docs.oasis-open.org/cmis/CMIS/
             v1.0/cs01/cmis-spec-v1.0.html>.
             Latest version available at
             <http://docs.oasis-open.org/cmis/CMIS/v1.0/
             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.
 [RFC5023]   Gregorio, J. and B. de hOra, "The Atom Publishing
             Protocol", RFC 5023, October 2007.

Brown, et al. Informational [Page 7] RFC 5829 Version Navigation Link Relations April 2010

 [WEB-LINKING]
             Nottingham, M., "Web Linking", Work in Progress,
             March 2010.

Brown, et al. Informational [Page 8] RFC 5829 Version Navigation Link Relations April 2010

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
    WebDAV: the resource identified by 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).

Brown, et al. Informational [Page 9] RFC 5829 Version Navigation Link Relations April 2010

 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 ([WEB-LINKING]) generalizes Atom link
 relations, and also reintroduces 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 a VERSION-CONTROL request ([RFC3253],
 Section 3.5) could expose a newly created version-history and
 checked-in version as link relations:
 >> Request:
 VERSION-CONTROL /docs/test.txt HTTP/1.1
 Host: example.net
 >> 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.)

Brown, et al. Informational [Page 10] RFC 5829 Version Navigation Link Relations April 2010

 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

Brown, et al. Informational [Page 11] RFC 5829 Version Navigation Link Relations April 2010

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
 Julian F. Reschke (editor)
 greenbytes GmbH
 Hafenweg 16
 Muenster, NW 48155
 Germany
 EMail: julian.reschke@greenbytes.de
 URI:   http://greenbytes.de/tech/webdav/

Brown, et al. Informational [Page 12]

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