Network Working Group A. B. Brown
Internet-Draft G. Clemm
Intended status: Informational IBM
Expires: May 22, 2010 J. F. Reschke, Ed.
greenbytes
November 20, 2009

Link Relations for Simple Version Navigation
draft-brown-versioning-link-relations-03

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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This Internet-Draft will expire on May 22, 2010.

Copyright Notice

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Table of Contents

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

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. 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.

3.5. 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
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. 'predecessor-version' Link Relation Registration

Attribute Value:
predecessor-version
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. 'successor-version' Link Relation Registration

Attribute Value:
successor-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.

5. 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). Such agents should also take care to detect circular references.

6. References

6.1. Normative References

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

6.2. Informative References

[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.
[JSR-283] Day SoftwareNuescheler, D. and P. Piegaze, "Content Repository API for Java™ Technology Specification", Java Specification Request 283, August 2009.
[draft-nottingham-http-link-header] Nottingham, M., "Web Linking", Internet-Draft draft-nottingham-http-link-header-06, 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

latest-version

working-resource

predecessor-version

successor-version

Appendix 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

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)

Appendix 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.

Appendix 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.

Appendix C.3. Since draft-brown-link-relations-02

Add and resolve issue "iana".

Appendix D. Resolved issues (to be removed by RFC Editor before publication)

Issues that were either rejected or resolved in this version of this document.

Appendix D.1. iana

Type: change

julian.reschke@greenbytes.de (2009-11-20): Use proper IANA registration template.

Appendix E. Open issues (to be removed by RFC Editor prior to publication)

Appendix E.1. edit

Type: edit

julian.reschke@greenbytes.de (2009-11-19): Umbrella issue for editorial fixes/enhancements.

Authors' Addresses

Al Brown IBM 3565 Harbor Blvd Costa Mesa, California 92626 US EMail: albertcbrown@us.ibm.com
Geoffrey Clemm IBM 20 Maguire Road Lexington, MA 02421 US 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/