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: [email protected]


  Geoffrey Clemm
  IBM
  20 Maguire Road
  Lexington, MA 02421
  USA

  EMail: [email protected]


  Julian F. Reschke (editor)
  greenbytes GmbH
  Hafenweg 16
  Muenster, NW 48155
  Germany

  EMail: [email protected]
  URI:   http://greenbytes.de/tech/webdav/























Brown, et al.                 Informational                    [Page 12]

You are viewing proxied material from gopher.fnord.one. The copyright of proxied material belongs to its original authors. Any comments or complaints in relation to proxied material should be directed to the original authors of the content concerned. Please see the disclaimer for more details.