Link Relations for Simple Version Navigation

Abstract

This specification defines Atom link relations for navigation between a resource and its versions.¶

Status of this Memo

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Copyright Notice

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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.¶

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 are to be registered by IANA per [RFC4287]. [lhdraft: Will be updated to follow [draft-nottingham-http-link-header] once approved by the IESG. --jre] ¶

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

[RFC4287]: Nottingham, M. and R. Sayre, “The Atom Syndication Format”, RFC 4287, December 2005.

6.2. Informative References

[draft-nottingham-http-link-header]: Nottingham, M., “Web Linking”, Internet-Draft draft-nottingham-http-link-header-06 (work in progress), July 2009.
[JSR-283]: Day Software, Nuescheler, D., and P. Piegaze, “Content Repository API for Java™ 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.

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-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], 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], 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

>> 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

Link Relations for Simple Version Navigation

Abstract

Status of this Memo

Copyright Notice

Editorial Note (To be removed by RFC Editor before publication)

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