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Internet Engineering Task Force (IETF)                          A. BrownRequest for Comments: 5829                                      G. ClemmCategory: Informational                                              IBMISSN: 2070-1721                                          J. Reschke, Ed.                                                              greenbytes                                                              April 2010Link Relation Types for Simple Version Navigation between Web ResourcesAbstract   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; seeSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://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 toBCP 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 2010Table of Contents1. Introduction ....................................................32. Terminology .....................................................33. Link Relations ..................................................43.1. 'version-history' ..........................................43.2. 'latest-version' ...........................................43.3. 'working-copy' .............................................43.4. 'working-copy-of' ..........................................43.5. 'predecessor-version' ......................................43.6. 'successor-version' ........................................54. IANA Considerations .............................................54.1. 'version-history' Link Relation Registration ...............54.2. 'latest-version' Link Relation Registration ................54.3. 'working-copy' Link Relation Registration ..................54.4. 'working-copy-of' Link Relation Registration ...............64.5. 'predecessor-version' Link Relation Registration ...........64.6. 'successor-version' Link Relation Registration .............65. Security Considerations .........................................66. Acknowledgments .................................................77. References ......................................................77.1. Normative References .......................................77.2. Informative References .....................................7Appendix A.  Relationship to Java Content Repository (JCR) and                WebDAV ................................................9A.1.  Example: Use of Link Relations in HTTP Link Header .......10Brown, et al.                 Informational                     [Page 2]

RFC 5829            Version Navigation Link Relations         April 20101.  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 perSection 7.1   of [RFC4287]:4.1.  'version-history' Link Relation Registration   Attribute Value:  version-history   Description:  SeeSection 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:  SeeSection 5.4.2.  'latest-version' Link Relation Registration   Attribute Value:  latest-version   Description:  SeeSection 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:  SeeSection 5.4.3.  'working-copy' Link Relation Registration   Attribute Value:  working-copy   Description:  SeeSection 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:  SeeSection 5.4.4.  'working-copy-of' Link Relation Registration   Attribute Value:  working-copy-of   Description:  SeeSection 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:  SeeSection 5.4.5.  'predecessor-version' Link Relation Registration   Attribute Value:  predecessor-version   Description:  SeeSection 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:  SeeSection 5.4.6.  'successor-version' Link Relation Registration   Attribute Value:  successor-version   Description:  SeeSection 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:  SeeSection 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 (seeSection 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.  References7.1.  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 2010Appendix A.  Relationship to Java Content Repository (JCR) and WebDAV   The link relations defined inSection 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], Sections5.2.1 and5.3.1).      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],Section3.3.1), 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], Sections3.3.2 and3.4.1).      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-versionBrown, et al.                 Informational                    [Page 11]

RFC 5829            Version Navigation Link Relations         April 2010Authors' 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]