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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/