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Douglass 3 Internet-Draft Spherical Cow Group 4 Updates: 5545 (if approved) February 3, 2017 5 Intended status: Standards Track 6 Expires: August 7, 2017 8 Support for iCalendar Relationships 9 draft-ietf-calext-ical-relations-01 11 Abstract 13 This specification updates RELATED-TO and introduces new iCalendar 14 properties LINK, STRUCTURED-CATEGORY and REFID to allow better 15 linking and grouping of iCalendar components and related data. 17 Status of This Memo 19 This Internet-Draft is submitted in full conformance with the 20 provisions of BCP 78 and BCP 79. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF). Note that other groups may also distribute 24 working documents as Internet-Drafts. The list of current Internet- 25 Drafts is at http://datatracker.ietf.org/drafts/current/. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 This Internet-Draft will expire on August 7, 2017. 34 Copyright Notice 36 Copyright (c) 2017 IETF Trust and the persons identified as the 37 document authors. All rights reserved. 39 This document is subject to BCP 78 and the IETF Trust's Legal 40 Provisions Relating to IETF Documents 41 (http://trustee.ietf.org/license-info) in effect on the date of 42 publication of this document. Please review these documents 43 carefully, as they describe your rights and restrictions with respect 44 to this document. Code Components extracted from this document must 45 include Simplified BSD License text as described in Section 4.e of 46 the Trust Legal Provisions and are provided without warranty as 47 described in the Simplified BSD License. 49 Table of Contents 51 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 52 1.1. Structured iCalendar relationships . . . . . . . . . . . 3 53 1.2. Grouped iCalendar relationships . . . . . . . . . . . . . 3 54 1.3. Structured category relationships . . . . . . . . . . . . 3 55 1.4. Linked relationships . . . . . . . . . . . . . . . . . . 3 56 1.5. Caching and offline use . . . . . . . . . . . . . . . . . 4 57 1.6. Conventions Used in This Document . . . . . . . . . . . . 4 58 2. Reference Types . . . . . . . . . . . . . . . . . . . . . . . 5 59 3. Link Relation Types . . . . . . . . . . . . . . . . . . . . . 5 60 4. Redefined Relation Type Value . . . . . . . . . . . . . . . . 5 61 5. New Property Parameters . . . . . . . . . . . . . . . . . . . 8 62 5.1. Rel . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 63 5.2. Gap . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 64 6. New Value Data Types . . . . . . . . . . . . . . . . . . . . 9 65 7. New Properties . . . . . . . . . . . . . . . . . . . . . . . 10 66 7.1. Structured-Category . . . . . . . . . . . . . . . . . . . 10 67 7.2. Link . . . . . . . . . . . . . . . . . . . . . . . . . . 11 68 7.3. Refid . . . . . . . . . . . . . . . . . . . . . . . . . . 13 69 8. Redefined RELATED-TO Property . . . . . . . . . . . . . . . . 13 70 8.1. RELATED-TO . . . . . . . . . . . . . . . . . . . . . . . 14 71 9. Security Considerations . . . . . . . . . . . . . . . . . . . 16 72 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 73 10.1. iCalendar Property Registrations . . . . . . . . . . . . 16 74 10.2. iCalendar Property Parameter Registrations . . . . . . . 16 75 10.3. iCalendar Value Data Type Registrations . . . . . . . . 16 76 10.4. iCalendar RELTYPE Value Registrations . . . . . . . . . 17 77 10.5. New Reference Type Registration . . . . . . . . . . . . 17 78 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 17 79 12. Normative References . . . . . . . . . . . . . . . . . . . . 18 80 Appendix A. Change log . . . . . . . . . . . . . . . . . . . . . 18 81 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 19 83 1. Introduction 85 iCalendar entities often need to be related to each other or to 86 associated meta-data. These relationships can take the following 87 forms 89 Structured iCalendar: iCalendar entities are related to each other 90 in some structured way, for example as parent, sibling, before, 91 after. 93 Grouped iCalendar: iCalendar entities are related to each other as a 94 group. CATEGORIES are often used for this purpose but are 95 problematic for application developers. 97 Linked: Entities are linked to each other through typed references. 99 1.1. Structured iCalendar relationships 101 The currently existing iCalendar [RFC5545] RELATED-TO property has no 102 support for temporal relationships as used by standard project 103 management tools. 105 The RELTYPE parameter is extended to take new values defining 106 temporal relationships, a GAP parameter is defined to provide lead 107 and lag values and RELATED-TO is extended to allow URI values. These 108 changes allow the RELATED-TO property to define a richer set of 109 relationships useful for project management. 111 1.2. Grouped iCalendar relationships 113 This specification defines a new REFID property which allows 114 arbitrary groups of entities to be associated with the same key 115 value. The presence of a REFID property imparts no meaning to the 116 event. It is merely a key to allow retrieval. 118 1.3. Structured category relationships 120 The introduction of STRUCTURED-CATEGORY allows a more structured 121 approach to categorization, with the possibility of namespaced and 122 path-like values. Unlike REFID the category imparts some meaning. 123 It is assumed that the value of this property will reference a well 124 defined category. 126 The current [RFC5545] CATEGORY property is used as a free form 127 'tagging' field. As such it is difficult to establish formal 128 relationships between components based on their category. 130 Rather than attempt to add semantics to the current property it 131 seeems best to continue its usage as an informal tag and establish a 132 new property with more constraints. 134 1.4. Linked relationships 136 The currently existing iCalendar standard [RFC5545] lacks a general 137 purpose method for referencing additional, external information 138 relating to calendar components. 140 This document proposes a method for referencing typed external 141 information that can provide additional information about an 142 iCalendar component. This new LINK property is closely aligned to 143 the LINK header defined in [RFC5988] 144 The LINK property defines a typed reference or relation to external 145 meta-data or related resources. By providing type and format 146 information as parameters, clients and servers are able to discover 147 interesting references and make use of them, perhaps for indexing or 148 the presentation of interesting links for the user. 150 It is often necessary to relate calendar components. The current 151 RELATED-TO property only allows for a UID which is inadequate for 152 many purposes. Allowing other types may help but might raise a 153 number of backward compatibility issues. The link property can link 154 components in different collections or even on different servers. 156 When publishing events it is useful to be able to refer back to the 157 source of that information. The actual event may have been consumed 158 from a feed or an ics file on a web site. A LINK property can 159 provide a reference to the originator of the event. 161 Beyond the need to relate elements temporally, project management 162 tools often need to be able to specify the relationships between the 163 various events and tasks which make up a project. The LINK property 164 provides such a mechanism. 166 The LINK property SHOULD NOT be treated as just another attachment. 167 The ATTACH property is being extended to handle server-side 168 management and stripping of inline data. Clients may choose to 169 handle attachments differently as they are often an integral part of 170 the message - for example, the agenda. See 171 [I-D.daboo-caldav-attachments] 173 1.5. Caching and offline use 175 To facilitate offline display the link type may identify important 176 pieces of data which should be downloaded in advance. 178 In general, the calendar entity should be self explanatory without 179 the need to download referenced meta-data such as a web page. 181 1.6. Conventions Used in This Document 183 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 184 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 185 "OPTIONAL" in this document are to be interpreted as described in 186 [RFC2119]. 188 2. Reference Types 190 The actual reference value can take three forms specified by the type 191 parameter 193 URI: The default type. This is a URI referring to the target. 195 UID: This allows for linking within a single collection and the 196 value is assumed to be another component within that collection. 198 REFERENCE: An xpointer. In an XML environment it may be necessary 199 to refer to an external XML artifact. The XPointer is defined in 200 [W3C.WD-xptr-xpointer-20021219] and allows addressing portions of 201 XML documents. 203 3. Link Relation Types 205 [RFC5988] defines two form of relation types, registered and 206 extension. Registered relation types are added to a registry defined 207 by [RFC5988] while extension relation types are specified as unique 208 unregistered URIs, (at least unregistered in the [RFC5988] registry). 210 The relation types defined here will be registered with IANA in 211 accordance with the specifications in [RFC5988]. 213 4. Redefined Relation Type Value 215 Relationship parameter type values are defined in section 3.2.15. of 216 [RFC5545]. This specification redefines that type to include the new 217 temporal relationship values FINISHTOSTART, FINISHTOFINISH, 218 STARTTOFINISH and STARTTOSTART. It also adds the DEPENDS-ON value to 219 provide a link to a component upon which the current component 220 depends. 222 Format Definition: 224 This property parameter is defined by the following notation: 226 reltypeparam = "RELTYPE" "=" 227 ("PARENT" ; Parent relationship - Default 228 / "CHILD" ; Child relationship 229 / "SIBLING" ; Sibling relationship 230 / "DEPENDS-ON" ; refers to previous task 231 / "REFID" ; Relationship based on REFID 232 / "STRUCTURED-CATEGORY" 233 ; Relationship based on STRUCTURED-CATEGORY 234 / "FINISHTOSTART" ; Temporal relationship 235 / "FINISHTOFINISH" ; Temporal relationship 236 / "STARTTOFINISH" ; Temporal relationship 237 / "STARTTOSTART" ; Temporal relationship 238 / iana-token ; Some other IANA-registered 239 ; iCalendar relationship type 240 / x-name) ; A non-standard, experimental 241 ; relationship type 243 Description: This parameter can be specified on a property that 244 references another related calendar component. The parameter may 245 specify the hierarchical relationship type of the calendar 246 component referenced by the property when the value is PARENT, 247 CHILD or SIBLING. If this parameter is not specified on an 248 allowable property, the default relationship type is PARENT. 249 Applications MUST treat x-name and iana-token values they don't 250 recognize the same way as they would the PARENT value. 252 This parameter defines the temporal relationship when the value is 253 one of the project management standard relationships 254 FINISHTOSTART, FINISHTOFINISH, STARTTOFINISH or STARTTOSTART. 255 This property will be present in the predecessor entity and will 256 refer to the successor entity. The GAP parameter specifies the 257 lead or lag time between the predecessor and the successor. In 258 the description of each temporal relationship below we refer to 259 Task-A which contains and controls the relationship and Task-B the 260 target of the relationship. 262 RELTYPE=PARENT: See [RFC5545] section 3.2.15. 264 RELTYPE=CHILD: See [RFC5545] section 3.2.15. 266 RELTYPE=SIBLING: See [RFC5545] section 3.2.15. 268 RELTYPE=DEPENDS-ON: Indicates that the current calendar component 269 depends on the referenced calendar component in some manner. For 270 example a task may be blocked waiting on the other, referenced, 271 task. 273 RELTYPE=REFID: Establishes a reference from the current component to 274 components with a REFID property which matches the value given in 275 the associated RELATED-TO property. 277 RELTYPE=STRUCTURED-CATEGORY: Establishes a reference from the 278 current component to components with a STRUCTURED-CATEGORY 279 property which matches the value given in the associated RELATED- 280 TO property. 282 RELTYPE=FINISHTOSTART: Task-B cannot start until Task-A finishes. 283 For example, when sanding is complete, painting can begin. 285 ============ 286 | Task-A |--+ 287 ============ | 288 | 289 V 290 ============ 291 | Task-B | 292 ============ 294 Figure 1: Finish to start relationship 296 RELTYPE=FINISHTOFINISH: Task-B cannot finish before Task-A is 297 finished, that is the end of Task-A defines the end of Task-B. 298 For example, we start the potatoes, then the meat then the peas 299 but they should all be cooked at the same time. 301 ============ 302 | Task-A |--+ 303 ============ | 304 | 305 ============ | 306 | Task-B |<-+ 307 ============ 309 Figure 2: Finish to finish relationship 311 RELTYPE=STARTTOFINISH: The start of Task-A (which occurs after Task- 312 B) controls the finish of Task-B. For example, ticket sales 313 (Task-B) end when the game starts (Task-A). 315 ============ 316 +--| Task-A | 317 | ============ 318 | 319 ============ | 320 | Task-B |<-+ 321 ============ 323 Figure 3: Start to finish relationship 325 RELTYPE=STARTTOSTART: The start of Task-A triggers the start of 326 Task-B, that is Task-B can start anytime after Task-A starts. 328 ============ 329 +--| Task-A | 330 | ============ 331 | 332 | ============ 333 +->| Task-B | 334 ============ 336 Figure 4: Start to start relationship 338 5. New Property Parameters 340 5.1. Rel 342 Parameter name: REL 344 Purpose: To specify the relationship of data referenced by a LINK 345 property. 347 Format Definition: 349 This parameter is defined by the following notation: 351 relparam = "REL" "=" 352 ("SOURCE" ; Link to source of this component 353 / DQUOTE uri DQUOTE 354 / x-name ; Experimental reference type 355 / iana-token) ; Other IANA registered type 357 Description: This parameter MUST be specified on all LINK 358 properties, and defines the type of reference. This allows 359 programs consuming this data to automatically scan for references 360 they support. In addition to the values defined here any value 361 defined in [RFC5988] may be used. There is no default relation 362 type. 364 REL=SOURCE: identifies the source of the event information. 366 Registration: These relation types are registered in [RFC5988] 368 5.2. Gap 370 Parameter name: GAP 372 Purpose: To specify the length of the gap, positive or negative 373 between two temporally related components. 375 Format Definition: 377 This parameter is defined by the following notation: 379 gapparam = "GAP" "=" dur-value 381 Description: This parameter MAY be specified on the RELATED-TO 382 property, and defines the duration of time between the predecessor 383 and successor in an interval. When positive it defines the lag 384 time between a task and its logical successor. When negative it 385 defines the lead time. 387 An example of lag time might be if task A is "paint the room" and 388 task B is "hang the drapes" then task A may be related to task B 389 with RELTYPE=FINISHTOSTART with a gap long enough for the paint to 390 dry. 392 An example of lead time might be to relate a 1 week task A to the 393 end of task B with RELTYPE=STARTTOFINISH and a negative gap of 1 394 week so they finish at the same time. 396 6. New Value Data Types 398 This specification defines the following new value types to be used 399 with the VALUE property parameter: 401 UID VALUE=UID indicates that the associated value is the UID for a 402 component. 404 REFERENCE VALUE=REFERENCE indicates that the associated value is an 405 xpointer referencing an associated XML artifact. 407 7. New Properties 409 7.1. Structured-Category 411 Property name: STRUCTURED-CATEGORY 413 Purpose: This property defines the formal categories for a calendar 414 component. 416 Value type: URI 418 Property Parameters: IANA, and non-standard parameters can be 419 specified on this property. 421 Conformance: This property can be specified zero or more times in 422 any iCalendar component. 424 Description: This property is used to specify formal categories or 425 classifications of the calendar component. The values are useful 426 in searching for a calendar component of a particular type and 427 category. 429 Within the "VEVENT", "VTODO", or "VJOURNAL" calendar components, 430 more than one formal category can be specified by using multiple 431 properties. 433 This categorization is distinct from the more informal "tagging" 434 of components provided by the existing CATEGORIES property. It is 435 expected that the value of the STRUCTURED-CATEGORY property will 436 reference an external resource which provides information about 437 the categorization. 439 Possible category resources are the various proprietary systems, 440 for example Library of Congress, or an open source such as 441 dmoz.org. 443 In addition, a structured URI value allows for hierarchical 444 categorization of events. 446 Format Definition: 448 This property is defined by the following notation: 450 structured-category = "STRUCTURED-CATEGORY" structcatparam ":" uri CRLF 452 structcatparam = *( 453 ; 454 ; The following is OPTIONAL, 455 ; and MAY occur more than once. 456 ; 457 (";" other-param) 458 ; 459 ) 461 Example: 463 The following is an example of this property. It points to a server 464 acting as the source for the calendar object. 466 STRUCTURED-CATEGORY:http://example.com/event-types/sports 467 STRUCTURED-CATEGORY:http://example.com/event-types/arts/music 468 STRUCTURED-CATEGORY:http://example.com/task-types/delivery 470 7.2. Link 472 Property name: LINK 474 Purpose: This property provides a reference to external information 475 about a component. 477 Value type: URI, TEXT or REFERENCE 479 Property Parameters: Non-standard, reference type or format type 480 parameters can be specified on this property. 482 Conformance: This property MAY be specified in any iCalendar 483 component. 485 Description: When used in a component the value of this property 486 points to additional information related to the component. For 487 example, it may reference the originating web server. 489 Format Definition: 491 This property is defined by the following notation: 493 link = "LINK" linkparam / 494 ( 495 ";" "VALUE" "=" "TEXT" 496 ":" text 497 ) 498 ( 499 ";" "VALUE" "=" "REFERENCE" 500 ":" text 501 ) 502 ( 503 ";" "VALUE" "=" "URI" 504 ":" uri 505 ) 506 CRLF 508 linkparam = *( 510 ; the following is MANDATORY 511 ; and MAY occur more than once 513 (";" relparam) / 515 ; the following are MANDATORY 516 ; but MUST NOT occur more than once 518 (";" fmttypeparam) / 519 (";" labelparam) / 520 ; labelparam is defined in ... 522 ; the following is OPTIONAL 523 ; and MAY occur more than once 525 (";" xparam) 527 ) 529 Example: 531 The following is an example of this property. It points to a server 532 acting as the source for the calendar object. 534 LINK;REL=SOURCE;LABEL=The Egg:http://example.com/events 536 7.3. Refid 538 Property name: REFID 540 Purpose: This property value acts as a key for associated iCalendar 541 entities. 543 Value type: TEXT 545 Property Parameters: Non-standard parameters can be specified on 546 this property. 548 Conformance: This property MAY be specified multiple times in any 549 iCalendar component. 551 Description: The value of this property is a text identifier that 552 allows associated components to be located or retrieved as a 553 whole. For example all of the events in a travel itinerary would 554 have the same REFID value. 556 Format Definition: 558 This property is defined by the following notation: 560 refid = "REFID" refidparam ":" text CRLF 562 refidparam = *( 564 ; the following is OPTIONAL 565 ; and MAY occur more than once 567 (";" xparam) 569 ) 571 Example: 573 The following is an example of this property. 575 REFID:itinerary-2014-11-17 577 8. Redefined RELATED-TO Property 578 8.1. RELATED-TO 580 Property name: RELATED-TO 582 Purpose: This property is used to represent a relationship or 583 reference between one calendar component and another. The 584 definition here extends the definition in Section 3.8.4.5. of 585 [RFC5545] by allowing URI or UID values and a GAP parameter. 587 Value type: URI, UID or TEXT 589 Property Parameters: Non-standard, reference type, gap, value or 590 format type parameters can be specified on this property. 592 Conformance: This property MAY be specified in any iCalendar 593 component. 595 Description: By default or when VALUE=UID is specified, the property 596 value consists of the persistent, globally unique identifier of 597 another calendar component. This value would be represented in a 598 calendar component by the "UID" property. 600 By default, the property value points to another calendar 601 component that has a PARENT relationship to the referencing 602 object. The "RELTYPE" property parameter is used to either 603 explicitly state the default PARENT relationship type to the 604 referenced calendar component or to override the default PARENT 605 relationship type and specify either a CHILD or SIBLING 606 relationship or a temporal relationship. 608 The PARENT relationship indicates that the calendar component is a 609 subordinate of the referenced calendar component. The CHILD 610 relationship indicates that the calendar component is a superior 611 of the referenced calendar component. The SIBLING relationship 612 indicates that the calendar component is a peer of the referenced 613 calendar component. 615 The FINISHTOSTART, FINISHTOFINISH, STARTTOFINISH or STARTTOSTART 616 relationships define temporal relationships as specified in the 617 reltype parameter definition. 619 Changes to a calendar component referenced by this property can 620 have an implicit impact on the related calendar component. For 621 example, if a group event changes its start or end date or time, 622 then the related, dependent events will need to have their start 623 and end dates changed in a corresponding way. Similarly, if a 624 PARENT calendar component is cancelled or deleted, then there is 625 an implied impact to the related CHILD calendar components. This 626 property is intended only to provide information on the 627 relationship of calendar components. It is up to the target 628 calendar system to maintain any property implications of this 629 relationship. 631 Format Definition: 633 This property is defined by the following notation: 635 related = "RELATED-TO" relparam ( ":" text ) / 636 ( 637 ";" "VALUE" "=" "UID" 638 ":" uid 639 ) 640 ( 641 ";" "VALUE" "=" "URI" 642 ":" uri 643 ) 644 CRLF 646 relparam = *( 647 ; 648 ; The following are OPTIONAL, 649 ; but MUST NOT occur more than once. 650 ; 651 (";" reltypeparam) / 652 (";" gapparam) / 653 ; 654 ; The following is OPTIONAL, 655 ; and MAY occur more than once. 656 ; 657 (";" other-param) 658 ; 659 ) 661 Example: 663 The following are examples of this property. 665 RELATED-TO:jsmith.part7.19960817T083000.xyzMail@example.com 667 RELATED-TO:19960401-080045-4000F192713-0052@example.com 669 RELATED-TO;VALUE=URI;RELTYPE=STARTTOFINISH: 670 http://example.com/caldav/user/jb/cal/ 671 19960401-080045-4000F192713.ics 673 9. Security Considerations 675 Applications using the LINK property need to be aware of the risks 676 entailed in using the URIs provided as values. See [RFC3986] for a 677 discussion of the security considerations relating to URIs. 679 The STRUCTURED-CATEGORY and redefined RELATED-TO property have the 680 same issues in that values may be URIs. 682 10. IANA Considerations 684 10.1. iCalendar Property Registrations 686 The following iCalendar property names have been added to the 687 iCalendar Properties Registry defined in Section 8.3.2 of [RFC5545] 689 +---------------------+---------+-------------+ 690 | Property | Status | Reference | 691 +---------------------+---------+-------------+ 692 | LINK | Current | Section 7.2 | 693 | REFID | Current | Section 7.3 | 694 | STRUCTURED-CATEGORY | Current | Section 7.1 | 695 +---------------------+---------+-------------+ 697 10.2. iCalendar Property Parameter Registrations 699 The following iCalendar property parameter names have been added to 700 the iCalendar Parameters Registry defined in Section 8.3.3 of 701 [RFC5545] 703 +-----------+---------+-------------+ 704 | Parameter | Status | Reference | 705 +-----------+---------+-------------+ 706 | REL | Current | Section 5.1 | 707 | GAP | Current | Section 5.2 | 708 +-----------+---------+-------------+ 710 10.3. iCalendar Value Data Type Registrations 712 The following iCalendar property parameter names have been added to 713 the iCalendar Value Data Types Registry defined in Section 8.3.4 of 714 [RFC5545] 715 +-----------------+---------+-----------+ 716 | Value Data Type | Status | Reference | 717 +-----------------+---------+-----------+ 718 | UID | Current | Section 6 | 719 | REFERENCE | Current | Section 6 | 720 +-----------------+---------+-----------+ 722 10.4. iCalendar RELTYPE Value Registrations 724 The following iCalendar "RELTYPE" values have been added to the 725 iCalendar Relationship Types Registry defined in Section 8.3.8 of 726 [RFC5545] 728 +---------------------+---------+-----------+ 729 | Parameter | Status | Reference | 730 +---------------------+---------+-----------+ 731 | DEPENDS-ON | Current | Section 4 | 732 | REFID | Current | Section 4 | 733 | STRUCTURED-CATEGORY | Current | Section 4 | 734 | FINISHTOSTART | Current | Section 4 | 735 | FINISHTOFINISH | Current | Section 4 | 736 | STARTTOFINISH | Current | Section 4 | 737 | STARTTOSTART | Current | Section 4 | 738 +---------------------+---------+-----------+ 740 10.5. New Reference Type Registration 742 The following link relation values have been added to the Reference 743 Types Registry defined in Section 6.2.2 of [RFC5988] 745 +--------+---------+-------------+ 746 | Name | Status | Reference | 747 +--------+---------+-------------+ 748 | SOURCE | Current | Section 5.1 | 749 +--------+---------+-------------+ 751 11. Acknowledgements 753 The author would like to thank the members of the Calendaring and 754 Scheduling Consortium technical committees and the following 755 individuals for contributing their ideas, support and comments: 757 Adrian Apthorp, Cyrus Daboo, Marten Gajda, Ken Murchison 759 The author would also like to thank the Calendaring and Scheduling 760 Consortium for advice with this specification. 762 12. Normative References 764 [I-D.daboo-caldav-attachments] 765 Daboo, C. and A. Quillaud, "CalDAV Managed Attachments", 766 draft-daboo-caldav-attachments-03 (work in progress), 767 February 2014. 769 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 770 Requirement Levels", BCP 14, RFC 2119, 771 DOI 10.17487/RFC2119, March 1997, 772 . 774 [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, 775 DOI 10.17487/RFC3688, January 2004, 776 . 778 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 779 Resource Identifier (URI): Generic Syntax", STD 66, 780 RFC 3986, DOI 10.17487/RFC3986, January 2005, 781 . 783 [RFC5545] Desruisseaux, B., Ed., "Internet Calendaring and 784 Scheduling Core Object Specification (iCalendar)", 785 RFC 5545, DOI 10.17487/RFC5545, September 2009, 786 . 788 [RFC5988] Nottingham, M., "Web Linking", RFC 5988, 789 DOI 10.17487/RFC5988, October 2010, 790 . 792 [W3C.REC-xml-20060816] 793 Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E., and 794 F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fourth 795 Edition)", World Wide Web Consortium Recommendation REC- 796 xml-20060816, August 2006, 797 . 799 [W3C.WD-xptr-xpointer-20021219] 800 DeRose, S., Daniel, R., and E. Maler, "XPointer xpointer() 801 Scheme", World Wide Web Consortium WD WD-xptr-xpointer- 802 20021219, December 2002, 803 . 805 Appendix A. Change log 807 V04: 2014-11-18 MD 809 o Add 5545 registrations. 811 o Drop Q-name in favor of URI. 813 o Change REFID value type to text. 815 o Add STRUCTURED-CATEGORY property. 817 o Add STRUCTURED-CATEGORY relationship to RELATED-TO. 819 V03: 2014-09-21 MD 821 o Added Q-name specification. 823 o Change RELATED-ID to REFID and change its value type to Q-name. 825 o Add REFID relationship to RELATED-TO. 827 V02: 2013-11-22 MD 829 o Added more description to GAP 831 V01: 2013-09-26 MD 833 o Removed "Improved" from title 835 o Fixed typos and examples 837 o Removed gap param from link 839 2013-06-02 MD Initial version 841 Author's Address 843 Michael Douglass 844 Spherical Cow Group 845 226 3rd Street 846 Troy, NY 12180 847 USA 849 Email: mdouglass@sphericalcowgroup.com 850 URI: http://sphericalcowgroup.com