Link Relations for Simple Version Navigation
draft-brown-versioning-link-relations-02

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/).

Status of this Memo

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Table of Contents

1.  Introduction
2.  Terminology
3.  Link Relations
4.  Security Considerations
5.  IANA Considerations
6.  References
    6.1.  Normative References
    6.2.  Informative References
Appendix A.  Relationship to Java Content Repository (JCR) and WebDAV
    A.1.  Example: Use of Link Relations in HTTP Link Header
Appendix B.  Contributors
Appendix C.  Change Log (to be removed by RFC Editor before publication)
    C.1.  Since draft-brown-link-relations-00
    C.2.  Since draft-brown-link-relations-01
§  Authors' Addresses

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.

2.  Terminology

Versioned Resource

When a resource is put under version control, it becomes a "versioned resource". A versioned resource can be "checked out" to allow modification.

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 modified to create a new version of a versioned resource.

3.  Link Relations

The following link relations are defined:

version-history

When included on a versioned resource, this link points to a resource containing the version history for this resource.

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.

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.

predecessor-version

When included on a versioned resource, this link points to a resource containing the predecessor version in the version history.

Some systems may allow multiple of these link relations in the case of a multiple branches merging.

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.  Security Considerations

Automated agents should take care when these relation crosses administrative domains (e.g., the URI has a different authority than the current document).

5.  IANA Considerations

The link relations defined in Section 3 (Link Relations) are to be registered by IANA per [RFC4287] (Nottingham, M. and R. Sayre, “The Atom Syndication Format,” December 2005.). [lhdraft] (jre: Will be updated to follow [draft-nottingham-http-link-header] once approved by the IESG.)

All link relations defined in this document will have the following expected display characteristics:

Undefined; this relation can be used for background processing or to provide extended functionality without displaying its value.

6.  References

6.1. Normative References

6.2. Informative References

Appendix A.  Relationship to Java Content Repository (JCR) and WebDAV

The link relations defined in Section 3 (Link Relations) correspond to various properties used in WebDAV Versioning [RFC3253] (Clemm, G., Amsden, J., Ellison, T., Kaler, C., and J. Whitehead, “Versioning Extensions to WebDAV (Web Distributed Authoring and Versioning),” March 2002.) and JCR [JSR‑283] (Day Software, Nuescheler, D., and P. Piegaze, “Content Repository API for Java™ Technology Specification,” August 2009.):

version-history

WebDAV: the resource identified by the DAV:version-history property ([RFC3253] (Clemm, G., Amsden, J., Ellison, T., Kaler, C., and J. Whitehead, “Versioning Extensions to WebDAV (Web Distributed Authoring and Versioning),” March 2002.), Sections 5.2.1 and 5.3.1).

JCR: the node identified by jcr:versionHistory property ([JSR‑283] (Day Software, Nuescheler, D., and P. Piegaze, “Content Repository API for Java™ Technology Specification,” August 2009.), 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] (Clemm, G., Amsden, J., Ellison, T., Kaler, C., and J. Whitehead, “Versioning Extensions to WebDAV (Web Distributed Authoring and Versioning),” March 2002.), Section 3.2.1) or DAV:checked-out ([RFC3253] (Clemm, G., Amsden, J., Ellison, T., Kaler, C., and J. Whitehead, “Versioning Extensions to WebDAV (Web Distributed Authoring and Versioning),” March 2002.), 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] (Day Software, Nuescheler, D., and P. Piegaze, “Content Repository API for Java™ Technology Specification,” August 2009.), Section 3.13.2.5) for versionable nodes; for version nodes, a successor version that itself does not have any successors.

working-resource

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] (Clemm, G., Amsden, J., Ellison, T., Kaler, C., and J. Whitehead, “Versioning Extensions to WebDAV (Web Distributed Authoring and Versioning),” March 2002.), Section 3.4.3).

JCR: for checked-out versionable nodes: the node itself.

predecessor-version

WebDAV: each resource identified by a member of DAV:predecessor-set ([RFC3253] (Clemm, G., Amsden, J., Ellison, T., Kaler, C., and J. Whitehead, “Versioning Extensions to WebDAV (Web Distributed Authoring and Versioning),” March 2002.), Sections 3.3.2 and 3.4.1).

JCR: each node identified by a member of jcr:predecessors ([JSR‑283] (Day Software, Nuescheler, D., and P. Piegaze, “Content Repository API for Java™ Technology Specification,” August 2009.), Section 3.13.3.3).

successor-version

WebDAV: each resource identified by a member of DAV:successor-set ([RFC3253] (Clemm, G., Amsden, J., Ellison, T., Kaler, C., and J. Whitehead, “Versioning Extensions to WebDAV (Web Distributed Authoring and Versioning),” March 2002.), Section 3.4.2).

JCR: each node identified by a member of jcr:successors ([JSR‑283] (Day Software, Nuescheler, D., and P. Piegaze, “Content Repository API for Java™ Technology Specification,” August 2009.), 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] (Nottingham, M., “Web Linking,” July 2009.)) 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] (Nottingham, M. and R. Sayre, “The Atom Syndication Format,” December 2005.)) or WebDAV properties ([RFC3253] (Clemm, G., Amsden, J., Ellison, T., Kaler, C., and J. Whitehead, “Versioning Extensions to WebDAV (Web Distributed Authoring and Versioning),” March 2002.)).

For instance, a response to an VERSION-CONTROL request ([RFC3253] (Clemm, G., Amsden, J., Ellison, T., Kaler, C., and J. Whitehead, “Versioning Extensions to WebDAV (Web Distributed Authoring and Versioning),” March 2002.), 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

>> Response:

HTTP/1.1 200 OK
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

Appendix B.  Contributors

The content and concepts within are a product of the Content Management Interoperability Services (CMIS) Technical Committee (TC) at OASIS.

All members of the TC have contributed.

Appendix C.  Change Log (to be removed by RFC Editor before publication)

C.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.

C.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.

Authors' Addresses