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2 Network Working Group A. Brown
3 Internet-Draft G. Clemm
4 Intended status: Informational IBM
5 Expires: June 7, 2010 J. Reschke, Ed.
6 greenbytes
7 December 04, 2009
9 Link Relations for Simple Version Navigation
10 draft-brown-versioning-link-relations-04
12 Abstract
14 This specification defines Atom link relations for navigation between
15 a resource and its versions.
17 Editorial Note (To be removed by RFC Editor before publication)
19 Please send comments to the Atom Syntax mailing list
20 ().
22 Note that although discussion takes place on the Atompub working
23 group's mailing list, this is not a working group document.
25 XML versions, latest edits and the issues list for this document are
26 available from .
29 Status of this Memo
31 This Internet-Draft is submitted to IETF in full conformance with the
32 provisions of BCP 78 and BCP 79.
34 Internet-Drafts are working documents of the Internet Engineering
35 Task Force (IETF), its areas, and its working groups. Note that
36 other groups may also distribute working documents as Internet-
37 Drafts.
39 Internet-Drafts are draft documents valid for a maximum of six months
40 and may be updated, replaced, or obsoleted by other documents at any
41 time. It is inappropriate to use Internet-Drafts as reference
42 material or to cite them other than as "work in progress."
44 The list of current Internet-Drafts can be accessed at
45 http://www.ietf.org/ietf/1id-abstracts.txt.
47 The list of Internet-Draft Shadow Directories can be accessed at
48 http://www.ietf.org/shadow.html.
50 This Internet-Draft will expire on June 7, 2010.
52 Copyright Notice
54 Copyright (c) 2009 IETF Trust and the persons identified as the
55 document authors. All rights reserved.
57 This document is subject to BCP 78 and the IETF Trust's Legal
58 Provisions Relating to IETF Documents
59 (http://trustee.ietf.org/license-info) in effect on the date of
60 publication of this document. Please review these documents
61 carefully, as they describe your rights and restrictions with respect
62 to this document. Code Components extracted from this document must
63 include Simplified BSD License text as described in Section 4.e of
64 the Trust Legal Provisions and are provided without warranty as
65 described in the BSD License.
67 Table of Contents
69 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
70 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
71 3. Link Relations . . . . . . . . . . . . . . . . . . . . . . . . 5
72 3.1. version-history . . . . . . . . . . . . . . . . . . . . . 5
73 3.2. latest-version . . . . . . . . . . . . . . . . . . . . . . 5
74 3.3. working-copy . . . . . . . . . . . . . . . . . . . . . . . 5
75 3.4. working-copy-of . . . . . . . . . . . . . . . . . . . . . 5
76 3.5. predecessor-version . . . . . . . . . . . . . . . . . . . 5
77 3.6. successor-version . . . . . . . . . . . . . . . . . . . . 6
78 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
79 4.1. 'version-history' Link Relation Registration . . . . . . . 6
80 4.2. 'latest-version' Link Relation Registration . . . . . . . 6
81 4.3. 'working-copy' Link Relation Registration . . . . . . . . 6
82 4.4. 'working-copy-of' Link Relation Registration . . . . . . . 7
83 4.5. 'predecessor-version' Link Relation Registration . . . . . 7
84 4.6. 'successor-version' Link Relation Registration . . . . . . 7
85 5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
86 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
87 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
88 7.1. Normative References . . . . . . . . . . . . . . . . . . . 8
89 7.2. Informative References . . . . . . . . . . . . . . . . . . 8
90 Appendix A. Relationship to Java Content Repository (JCR) and
91 WebDAV . . . . . . . . . . . . . . . . . . . . . . . 9
92 A.1. Example: Use of Link Relations in HTTP Link Header . . . . 10
93 Appendix B. Change Log (to be removed by RFC Editor before
94 publication) . . . . . . . . . . . . . . . . . . . . 11
95 B.1. Since draft-brown-link-relations-00 . . . . . . . . . . . 11
96 B.2. Since draft-brown-link-relations-01 . . . . . . . . . . . 12
97 B.3. Since draft-brown-link-relations-02 . . . . . . . . . . . 12
98 B.4. Since draft-brown-link-relations-03 . . . . . . . . . . . 12
99 Appendix C. Resolved issues (to be removed by RFC Editor
100 before publication) . . . . . . . . . . . . . . . . . 12
101 C.1. cmis . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
102 C.2. checked-out . . . . . . . . . . . . . . . . . . . . . . . 12
103 Appendix D. Open issues (to be removed by RFC Editor prior to
104 publication) . . . . . . . . . . . . . . . . . . . . 13
105 D.1. edit . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
106 D.2. working-copy-of . . . . . . . . . . . . . . . . . . . . . 13
107 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
109 1. Introduction
111 This specification defines link relations that may be used on a
112 resource that exists in a system that supports versioning to navigate
113 among the different resources available, such as past versions.
115 These link relations are used in the AtomPub ([RFC5023]) bindings of
116 the "Content Management Interoperability Services" (CMIS). See
117 Section 3.4.3.1 of [CMIS] for further information.
119 2. Terminology
121 Versioned Resource
123 When a resource is put under version control, it becomes a
124 "versioned resource". Many servers protect versioned resources
125 from modifications by considering them "checked in", and by
126 requiring a "checkout" operation before modification, and a
127 "checkin" operation to get back to the "checked-in" state. Other
128 servers allow modification, in which case the checkout/checkin
129 operation may happen implicitly.
131 Version History
133 A "version history" resource is a resource that contains all the
134 versions of a particular versioned resource.
136 Predecessor, Successor
138 When a versioned resource is checked out and then subsequently
139 checked in, the version that was checked out becomes a
140 "predecessor" of the version created by the checkin. A client can
141 specify multiple predecessors for a new version if the new version
142 is logically a merge of those predecessors. The inverse of the
143 predecessor relation is the "successor" relation. Therefore, if X
144 is a predecessor of Y, then Y is a successor of X.
146 Working Copy
148 A "working copy" is a resource at a server-defined URL that can be
149 used to create a new version of a versioned resource.
151 Checkout
153 A "checkout" is an operation on a versioned resource that creates
154 a working copy, or changes the versioned resource to be a working-
155 copy as well ("in-place versioning").
157 Checkin
159 A "checkin" is an operation on a working copy that creates a new
160 version of its corresponding versioned resource.
162 Note: the operations for putting a resource under version control,
163 and for checking in and checking out depend on the protocol in use
164 and are beyond the scope of this document; see [CMIS], [RFC3253]
165 and [JSR-283] for examples.
167 3. Link Relations
169 The following link relations are defined:
171 3.1. version-history
173 When included on a versioned resource, this link points to a resource
174 containing the version history for this resource.
176 3.2. latest-version
178 When included on a versioned resource, this link points to a resource
179 containing the latest (e.g., current) version.
181 The latest version is defined by the system. For linear versioning
182 systems, this is probably the latest version by timestamp. For
183 systems that support branching, there will be multiple latest
184 versions, one for each branch in the version history.
186 Some systems may allow multiple of these link relations.
188 3.3. working-copy
190 When included on a versioned resource, this link points to a working
191 copy for this resource.
193 Some systems may allow multiple of these link relations.
195 3.4. working-copy-of
197 When included on a working copy, this link points to the versioned
198 resource from which this working copy was obtained.
200 3.5. predecessor-version
202 When included on a versioned resource, this link points to a resource
203 containing the predecessor version in the version history.
205 Some systems may allow multiple of these link relations in the case
206 of a multiple branches merging.
208 3.6. successor-version
210 When included on a versioned resource, this link points to a resource
211 containing the successor version in the version history.
213 Some systems may allow multiple of these link relations in order to
214 support branching.
216 4. IANA Considerations
218 The link relations below are to be registered by IANA per Section 7.1
219 of [RFC4287]:
221 4.1. 'version-history' Link Relation Registration
223 Attribute Value: version-history
225 Description: See Section 3.1.
227 Expected display characteristics: Undefined; this relation can be
228 used for background processing or to provide extended
229 functionality without displaying its value.
231 Security considerations: See Section 5.
233 4.2. 'latest-version' Link Relation Registration
235 Attribute Value: latest-version
237 Description: See Section 3.2.
239 Expected display characteristics: Undefined; this relation can be
240 used for background processing or to provide extended
241 functionality without displaying its value.
243 Security considerations: See Section 5.
245 4.3. 'working-copy' Link Relation Registration
247 Attribute Value: working-copy
248 Description: See Section 3.3.
250 Expected display characteristics: Undefined; this relation can be
251 used for background processing or to provide extended
252 functionality without displaying its value.
254 Security considerations: See Section 5.
256 4.4. 'working-copy-of' Link Relation Registration
258 Attribute Value: working-copy-of
260 Description: See Section 3.4.
262 Expected display characteristics: Undefined; this relation can be
263 used for background processing or to provide extended
264 functionality without displaying its value.
266 Security considerations: See Section 5.
268 4.5. 'predecessor-version' Link Relation Registration
270 Attribute Value: predecessor-version
272 Description: See Section 3.5.
274 Expected display characteristics: Undefined; this relation can be
275 used for background processing or to provide extended
276 functionality without displaying its value.
278 Security considerations: See Section 5.
280 4.6. 'successor-version' Link Relation Registration
282 Attribute Value: successor-version
284 Description: See Section 3.6.
286 Expected display characteristics: Undefined; this relation can be
287 used for background processing or to provide extended
288 functionality without displaying its value.
290 Security considerations: See Section 5.
292 5. Security Considerations
294 Automated agents should take care when these relation crosses
295 administrative domains (e.g., the URI has a different authority than
296 the current document). Such agents should also take care to detect
297 circular references.
299 6. Acknowledgments
301 Thanks to the members of Content Management Interoperability Services
302 (CMIS) Technical Committee (TC) at OASIS for the initial proposal,
303 and to Jan Algermissen for feedback during IETF review.
305 7. References
307 7.1. Normative References
309 [RFC4287] Nottingham, M. and R. Sayre, "The Atom Syndication
310 Format", RFC 4287, December 2005.
312 7.2. Informative References
314 [CMIS] Brown, A., Gur-Esh, E., McVeigh, R., and F. Muller,
315 "Content Management Interoperability Services (CMIS)
316 Version 1.0", OASIS CMIS v1.0 Committee Draft 04,
317 September 2009, .
320 [JSR-283] Day Software, Nuescheler, D., and P. Piegaze, "Content
321 Repository API for Java(tm) Technology Specification",
322 Java Specification Request 283, August 2009,
323 .
325 [RFC3253] Clemm, G., Amsden, J., Ellison, T., Kaler, C., and J.
326 Whitehead, "Versioning Extensions to WebDAV (Web
327 Distributed Authoring and Versioning)", RFC 3253,
328 March 2002.
330 [RFC5023] Gregorio, J. and B. de hOra, "The Atom Publishing
331 Protocol", RFC 5023, October 2007.
333 [draft-nottingham-http-link-header]
334 Nottingham, M., "Web Linking",
335 draft-nottingham-http-link-header-06 (work in progress),
336 July 2009.
338 Appendix A. Relationship to Java Content Repository (JCR) and WebDAV
340 The link relations defined in Section 3 correspond to various
341 properties used in WebDAV Versioning [RFC3253] and JCR [JSR-283]:
343 version-history
345 WebDAV: the resource identified by the DAV:version-history
346 property ([RFC3253], Sections 5.2.1 and 5.3.1).
348 JCR: the node identified by jcr:versionHistory property
349 ([JSR-283], Section 3.13.2.4) for versionable nodes, the parent
350 folder for version nodes.
352 latest-version
354 WebDAV: for version-controlled resources, DAV:checked-in
355 ([RFC3253], Section 3.2.1) or DAV:checked-out ([RFC3253], Section
356 3.3.1), depending on checkin state. For version resources, a
357 successor version that itself does not have any successors.
359 JCR: the version node identified by the jcr:baseVersion property
360 ([JSR-283], Section 3.13.2.5) for versionable nodes; for version
361 nodes, a successor version that itself does not have any
362 successors.
364 working-copy
366 WebDAV: for version-controlled resources that are checked-out in
367 place: the resource itself. For version resources: each resource
368 identified by a member of the DAV:checkout-set property (see
369 [RFC3253], Section 3.4.3).
371 JCR: for checked-out versionable nodes: the node itself.
373 working-copy-of
375 WebDAV: the resource identified by the the DAV:checked-out
376 property (see [RFC3253], Section 3.3.1).
378 JCR: for checked-out versionable nodes: the node identified by the
379 jcr:baseVersion property ([JSR-283], Section 3.13.12.5).
381 predecessor-version
383 WebDAV: each resource identified by a member of DAV:predecessor-
384 set ([RFC3253], Sections 3.3.2 and 3.4.1).
386 JCR: each node identified by a member of jcr:predecessors
387 ([JSR-283], Section 3.13.3.3).
389 successor-version
391 WebDAV: each resource identified by a member of DAV:successor-set
392 ([RFC3253], Section 3.4.2).
394 JCR: each node identified by a member of jcr:successors
395 ([JSR-283], Section 3.13.3.4).
397 A.1. Example: Use of Link Relations in HTTP Link Header
399 The "Web Linking" specification ([draft-nottingham-http-link-header])
400 generalizes Atom link relations, and also re-introduces the HTTP
401 "Link" header as a way to expose link relations in HTTP responses.
402 This will make it possible to expose version links independently from
403 a specific vocabulary, be it the Atom Feed Format ([RFC4287]) or
404 WebDAV properties ([RFC3253]).
406 For instance, a response to an VERSION-CONTROL request ([RFC3253],
407 Section 3.5) could expose newly created version-history and
408 checked-in version as link relations:
410 >> Request:
412 VERSION-CONTROL /docs/test.txt HTTP/1.1
413 Host: example.net
415 >> Response:
417 HTTP/1.1 200 OK
418 Link: ; rel=latest-version;
419 anchor=
420 Link: ; rel=version-history;
421 anchor=
423 (Note that in this case, the anchor parameter is used, as the
424 response to a VERSION-CONTROL request is not a representation of the
425 resource at the Request-URI)
427 A subsequent HEAD request on that resource could expose the version-
428 history and latest-version relations as well:
430 >> Request:
432 HEAD /docs/test.txt HTTP/1.1
433 Host: example.net
435 >> Response:
437 HTTP/1.1 200 OK
438 Content-Type: text/plain; charset=UTF-8
439 Content-Length: 12345
440 Link: ; rel=latest-version
441 Link: ; rel=version-history
443 After creating more versions, following the latest-version would then
444 expose predecessors of a version:
446 >> Request:
448 HEAD /system/v/84345634/3 HTTP/1.1
449 Host: example.net
451 >> Response:
453 HTTP/1.1 200 OK
454 Content-Type: text/plain; charset=UTF-8
455 Content-Length: 12323
456 Link: ; rel=predecessor-version
458 Appendix B. Change Log (to be removed by RFC Editor before publication)
460 B.1. Since draft-brown-link-relations-00
462 Added Geoff Clemm as author.
464 Renamed link relation "all-versions" to "version-history". Fixed
465 description of "working-resource" relation to state that it appears
466 on a version resource.
468 B.2. Since draft-brown-link-relations-01
470 Rewrite terminology and link relations using simpler definitions that
471 can reflect versioning approaches different from WebDAV.
473 Add JCR/WebDAV property table. And reference to Web Linking draft
474 (for now informative) and examples showing use of the Link header.
476 B.3. Since draft-brown-link-relations-02
478 Add and resolve issue "iana".
480 B.4. Since draft-brown-link-relations-03
482 Fix typo ("working-resource" instead of "working-copy"). Add and
483 resolve issues "checked-out", "cmis" and "working-copy-of".
485 Appendix C. Resolved issues (to be removed by RFC Editor before
486 publication)
488 Issues that were either rejected or resolved in this version of this
489 document.
491 C.1. cmis
493 Type: edit
495 julian.reschke@greenbytes.de (2009-12-01): Add a pointer to the CMIS
496 spec, so AtomPub use cases become clearer.
498 Resolution (2009-12-01): Done.
500 C.2. checked-out
502 In Section 2:
504 Type: change
506
508 algermissen1971@mac.com (2009-11-24): It is not clear to me, what the
509 meaning of 'check out' and 'check in'. Also, the text (IMO) creates
510 the impression that versioning can only take place when 'check out'
511 and 'check in' are applied. However, a resource could also be
512 versioned by the server upon any modification made by a client
513 regardless of any 'checking out' or 'checking in'. The link
514 relations specified would still make sense.
516 Assuming that 'checking out' and 'checking in' are operations on
517 resources, I think the draft should address how clients achieve these
518 operations. This would at least involve another link relation and
519 specification how to use the linked resource to perform a checkout.
521 Resolution (2009-12-04): Rephrased terminology; added explanations
522 for checkin/checkout.
524 Appendix D. Open issues (to be removed by RFC Editor prior to
525 publication)
527 D.1. edit
529 Type: edit
531 julian.reschke@greenbytes.de (2009-11-19): Umbrella issue for
532 editorial fixes/enhancements.
534 D.2. working-copy-of
536 Type: change
538
540 algermissen1971@mac.com (2009-12-02): ...what is your opinion
541 regarding the introduction of a link relation that is the opposite of
542 working-copy in order to being able to find the versioned resource
543 that the working copy I have is a working copy of?
544 I am undecided regarding the necessity, but without a working-copy-of
545 relation it seems the client would need to maintain that information
546 (the relationship or the fact that a given resource is a working
547 copy) across requests.
549 Authors' Addresses
551 Al Brown
552 IBM
553 3565 Harbor Blvd
554 Costa Mesa, California 92626
555 US
557 Email: albertcbrown@us.ibm.com
558 Geoffrey Clemm
559 IBM
560 20 Maguire Road
561 Lexington, MA 02421
562 US
564 Email: geoffrey.clemm@us.ibm.com
566 Julian F. Reschke (editor)
567 greenbytes GmbH
568 Hafenweg 16
569 Muenster, NW 48155
570 Germany
572 Email: julian.reschke@greenbytes.de
573 URI: http://greenbytes.de/tech/webdav/