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Versions: 00 01 02 03 04 05 06 07 RFC 5829

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>.

Status of this Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on July 16, 2010.

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
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   the Trust Legal Provisions and are provided without warranty as
   described in the BSD License.



































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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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