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Douglass 3 Internet-Draft RPI 4 Intended status: Standards Track January 14, 2015 5 Expires: July 18, 2015 7 Support for Icalendar Relationships 8 draft-douglass-ical-relations-04 10 Abstract 12 This specification updates RELATED-TO and introduces new iCalendar 13 properties LINK, STRUCTURED-CATEGORY and REFID to allow better 14 linking and grouping of iCalendar components and related data. 16 Status of This Memo 18 This Internet-Draft is submitted in full conformance with the 19 provisions of BCP 78 and BCP 79. 21 Internet-Drafts are working documents of the Internet Engineering 22 Task Force (IETF). Note that other groups may also distribute 23 working documents as Internet-Drafts. The list of current Internet- 24 Drafts is at http://datatracker.ietf.org/drafts/current/. 26 Internet-Drafts are draft documents valid for a maximum of six months 27 and may be updated, replaced, or obsoleted by other documents at any 28 time. It is inappropriate to use Internet-Drafts as reference 29 material or to cite them other than as "work in progress." 31 This Internet-Draft will expire on July 18, 2015. 33 Copyright Notice 35 Copyright (c) 2015 IETF Trust and the persons identified as the 36 document authors. All rights reserved. 38 This document is subject to BCP 78 and the IETF Trust's Legal 39 Provisions Relating to IETF Documents 40 (http://trustee.ietf.org/license-info) in effect on the date of 41 publication of this document. Please review these documents 42 carefully, as they describe your rights and restrictions with respect 43 to this document. Code Components extracted from this document must 44 include Simplified BSD License text as described in Section 4.e of 45 the Trust Legal Provisions and are provided without warranty as 46 described in the Simplified BSD License. 48 Table of Contents 50 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 51 1.1. Structured iCalendar relationships . . . . . . . . . . . 3 52 1.2. Grouped iCalendar relationships . . . . . . . . . . . . . 3 53 1.3. Structured category relationships . . . . . . . . . . . . 3 54 1.4. Linked relationships . . . . . . . . . . . . . . . . . . 3 55 1.5. Caching and offline use . . . . . . . . . . . . . . . . . 4 56 1.6. Conventions Used in This Document . . . . . . . . . . . . 4 57 2. Reference Types . . . . . . . . . . . . . . . . . . . . . . . 4 58 3. Link Relation Types . . . . . . . . . . . . . . . . . . . . . 5 59 4. Redefined Relation Type Value . . . . . . . . . . . . . . . . 5 60 5. New Property Parameters . . . . . . . . . . . . . . . . . . . 8 61 5.1. Rel . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 62 5.2. Gap . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 63 6. New Value Data Types . . . . . . . . . . . . . . . . . . . . 9 64 7. New Properties . . . . . . . . . . . . . . . . . . . . . . . 9 65 7.1. Structured-Category . . . . . . . . . . . . . . . . . . . 9 66 7.2. Link . . . . . . . . . . . . . . . . . . . . . . . . . . 10 67 7.3. Refid . . . . . . . . . . . . . . . . . . . . . . . . . . 12 68 8. Redefined RELATED-TO Property . . . . . . . . . . . . . . . . 12 69 8.1. RELATED-TO . . . . . . . . . . . . . . . . . . . . . . . 13 70 9. Security Considerations . . . . . . . . . . . . . . . . . . . 15 71 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 72 10.1. iCalendar Property Registrations . . . . . . . . . . . . 15 73 10.2. iCalendar Property Parameter Registrations . . . . . . . 15 74 10.3. iCalendar Value Data Type Registrations . . . . . . . . 15 75 10.4. iCalendar RELTYPE Value Registrations . . . . . . . . . 16 76 10.5. New Reference Type Registration . . . . . . . . . . . . 16 77 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16 78 12. Normative References . . . . . . . . . . . . . . . . . . . . 17 79 Appendix A. Change log . . . . . . . . . . . . . . . . . . . . . 17 80 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 18 82 1. Introduction 84 Icalendar entities often need to be related to each other or to 85 associated meta-data. These relationships can take the following 86 forms 88 Structured iCalendar: Icalendar entities are related to each other 89 in some structured way, for example as parent, sibling, before, 90 after. 92 Grouped iCalendar: Icalendar entities are related to each other as a 93 group. CATEGORIES are often used for this purpose but are 94 problematic for application developers. 96 Linked: Entities are linked to each other through typed references. 98 1.1. Structured iCalendar relationships 100 The currently existing iCalendar [RFC5545] RELATED-TO property has no 101 support for temporal relationships as used by standard project 102 management tools. 104 The RELTYPE parameter is extended to take new values defining 105 temporal relationships, a GAP parameter is defined to provide lead 106 and lag values and RELATED-TO is extended to allow URI values. These 107 changes allows the RELATED-TO property to define a richer set of 108 relationships useful for project management. 110 1.2. Grouped iCalendar relationships 112 This specification defines a new REFID property which allows 113 arbitrary groups of entities to be associated with the same key 114 value. The presence of a REFID property imparts no meaning to the 115 event. It is merely a key to allow retrieval. 117 1.3. Structured category relationships 119 The introduction of STRUCTURED-CATEGORY allows a more structured 120 approach to categorization, with the possibility of namespaced and 121 path-like values. Unlike REFID the category imparts some meaning. 122 It is assumed that the value of this property will reference a well 123 defined category. 125 1.4. Linked relationships 127 The currently existing iCalendar standard [RFC5545] lacks a general 128 purpose method for referencing additional, external information 129 relating to calendar components. 131 This document proposes a method for referencing typed external 132 information that can provide additional information about an 133 iCalendar component. This new LINK property is closely aligned to 134 the LINK header defined in [RFC5988] 136 The LINK property defines a typed reference or relation to external 137 meta-data or related resources. By providing type and format 138 information as parameters, clients and servers are able to discover 139 interesting references and make use of them, perhaps for indexing or 140 the presentation of interesting links for the user. 142 It is often necessary to relate calendar components. The current 143 RELATED-TO property only allows for a UID which is inadequate for 144 many purposes. Allowing other types may help but might raise a 145 number of backward compatibility issues. The link property can link 146 components in different collections or even on different servers. 148 When publishing events it is useful to be able to refer back to the 149 source of that information. The actual event may have been consumed 150 from a feed or an ics file on a web site. A LINK property can 151 provide a reference to the originator of the event. 153 Beyond the need to relate elements temporally, project management 154 tools often need to be able to specify the relationships between the 155 various events and tasks which make up a project. The LINK property 156 provides such a mechanism. 158 The LINK property SHOULD NOT be treated as just another attachment. 159 The ATTACH property is being extended to handle server-side 160 management and stripping of inline data. Clients may choose to 161 handle attachments differently as they are often an integral part of 162 the message - for example, the agenda. 164 1.5. Caching and offline use 166 To facilitate offline display the link type may identify important 167 pieces of data which should be downloaded in advance. 169 In general, the calendar entity should be self explanatory without 170 the need to download referenced meta-data such as a web page. 172 1.6. Conventions Used in This Document 174 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 175 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 176 "OPTIONAL" in this document are to be interpreted as described in 177 [RFC2119]. 179 2. Reference Types 181 The actual reference value can take three forms specified by the type 182 parameter 184 URI: The default type. This is a URI referring to the target. 186 UID: This allows for linking within a single collection and the 187 value is assumed to be another component within that collection. 189 REFERENCE: An xpointer. In an XML environment it may be necessary 190 to refer to an external XML artifact. The XPointer is defined in 192 [W3C.WD-xptr-xpointer-20021219] and allows addressing portions of 193 XML documents. 195 3. Link Relation Types 197 [RFC5988] defines two form of relation types, registered and 198 extension. Registered relation types are added to a registry defined 199 by [RFC5988] while extension relation types are specified as unique 200 unregistered URIs, (at least unregistered in the [RFC5988] registry). 202 The relation types defined here will be registered with IANA in 203 accordance with the specifications in [RFC5988]. 205 4. Redefined Relation Type Value 207 Relationship parameter type values are defined in section 3.2.15. of 208 [RFC5545]. This specification redefines that type to include the new 209 temporal relationship values FINISHTOSTART, FINISHTOFINISH, 210 STARTTOFINISH and STARTTOSTART. It also adds the DEPENDS-ON value to 211 provide a link to an component upon which the current component 212 depends. 214 Format Definition: 216 This property parameter is defined by the following notation: 218 reltypeparam = "RELTYPE" "=" 219 ("PARENT" ; Parent relationship - Default 220 / "CHILD" ; Child relationship 221 / "SIBLING" ; Sibling relationship 222 / "DEPENDS-ON" ; refers to previous task 223 / "REFID" ; Relationship based on REFID 224 / "STRUCTURED-CATEGORY" 225 ; Relationship based on STRUCTURED-CATEGORY 226 / "FINISHTOSTART" ; Temporal relationship 227 / "FINISHTOFINISH" ; Temporal relationship 228 / "STARTTOFINISH" ; Temporal relationship 229 / "STARTTOSTART" ; Temporal relationship 230 / iana-token ; Some other IANA-registered 231 ; iCalendar relationship type 232 / x-name) ; A non-standard, experimental 233 ; relationship type 235 Description: This parameter can be specified on a property that 236 references another related calendar component. The parameter may 237 specify the hierarchical relationship type of the calendar 238 component referenced by the property when the value is PARENT, 239 CHILD or SIBLING. If this parameter is not specified on an 240 allowable property, the default relationship type is PARENT. 241 Applications MUST treat x-name and iana-token values they don't 242 recognize the same way as they would the PARENT value. 244 It defines the temporal relationship when the value is one of the 245 project management standard relationships FINISHTOSTART, 246 FINISHTOFINISH, STARTTOFINISH or STARTTOSTART. This property will 247 be present in the predecessor entity and will refer to the 248 successor entity. The GAP parameter specifies the lead or lag 249 time between the predecessor and the successor. In the 250 description of each temporal relationship below we refer to Task-A 251 which contains and controls the relationship and Task-B the target 252 of the relationship. 254 RELTYPE=PARENT: See [RFC5545] section 3.2.15. 256 RELTYPE=CHILD: See [RFC5545] section 3.2.15. 258 RELTYPE=SIBLING: See [RFC5545] section 3.2.15. 260 RELTYPE=DEPENDS-ON: Indicates that the current calendar component 261 depends on the referenced calendar component in some manner. For 262 example a task may be blocked waiting on the other, referenced, 263 task. 265 RELTYPE=REFID: Establishes a reference from the current component to 266 components with a REFID property which matches the value given in 267 the associated RELATED-TO property. 269 RELTYPE=STRUCTURED-CATEGORY: Establishes a reference from the 270 current component to components with a STRUCTURED-CATEGORY 271 property which matches the value given in the associated RELATED- 272 TO property. 274 RELTYPE=FINISHTOSTART: Task-B cannot start until Task-A finishes. 275 For example, when sanding is complete, painting can begin. 277 ============ 278 | Task-A |--+ 279 ============ | 280 | 281 V 282 ============ 283 | Task-B | 284 ============ 286 Figure 1: Finish to start relationship 288 RELTYPE=FINISHTOFINISH: Task-B cannot finish before Task-A is 289 finished, that is the end of Task-A defines the end of Task-B. 290 For example, we start the potatoes, then the meat then the peas 291 but they should all be cooked at the same time. 293 ============ 294 | Task-A |--+ 295 ============ | 296 | 297 ============ | 298 | Task-B |<-+ 299 ============ 301 Figure 2: Finish to finish relationship 303 RELTYPE=STARTTOFINISH: The start of Task-A (which occurs after Task- 304 B) controls the finish of Task-B. For example, ticket sales 305 (Task-B) end when the game starts (Task-A). 307 ============ 308 +--| Task-A | 309 | ============ 310 | 311 ============ | 312 | Task-B |<-+ 313 ============ 315 Figure 3: Start to finish relationship 317 RELTYPE=STARTTOSTART: The start of Task-A triggers the start of 318 Task-B, that is Task-B can start anytime after Task-A starts. 320 ============ 321 +--| Task-A | 322 | ============ 323 | 324 | ============ 325 +->| Task-B | 326 ============ 328 Figure 4: Start to start relationship 330 5. New Property Parameters 332 5.1. Rel 334 Parameter name: REL 336 Purpose: To specify the relationship of data referenced by a LINK 337 property. 339 Format Definition: 341 This parameter is defined by the following notation: 343 relparam = "REL" "=" 344 ("SOURCE" ; Link to source of this component 345 / DQUOTE uri DQUOTE 346 / x-name ; Experimental reference type 347 / iana-token) ; Other IANA registered type 349 Description: This parameter MUST be specified on all LINK 350 properties, and defines the type of reference. This allows 351 programs consuming this data to automatically scan for references 352 they support. In addition to the values defined here any value 353 defined in [RFC5988] may be used. There is no default relation 354 type. 356 REL=SOURCE: identifies the source of the event information. 358 Registration: These relation types are registered in [RFC5988] 360 5.2. Gap 362 Parameter name: GAP 364 Purpose: To specify the length of the gap, positive or negative 365 between two temporally related components. 367 Format Definition: 369 This parameter is defined by the following notation: 371 gapparam = "GAP" "=" dur-value 373 Description: This parameter MAY be specified on the RELATED-TO 374 property, and defines the duration of time between the predecessor 375 and successor in an interval. When positive it defines the lag 376 time between a task and its logical successor. When negative it 377 defines the lead time. 379 An example of lag time might be if task A is "paint the room" and 380 task B is "hang the drapes" then task A may be related to task B 381 with RELTYPE=FINISHTOSTART with a gap long enough for the paint to 382 dry. 384 An example of lead time might be to relate a 1 week task A to the 385 end of task B with RELTYPE=STARTTOFINISH and a negative gap of 1 386 week so they finish at the same time. 388 6. New Value Data Types 390 This specification defines the following new value types to be used 391 with the VALUE property parameter: 393 UID VALUE=UID indicates that the associated value is the UID for a 394 component. 396 REFERENCE VALUE=REFERENCE indicates that the associated value is an 397 xpointer referencing an associated XML artifact. 399 7. New Properties 401 7.1. Structured-Category 403 Property name: STRUCTURED-CATEGORY 405 Purpose: This property defines the formal categories for a calendar 406 component. 408 Value type: URI 410 Property Parameters: IANA, and non-standard parameters can be 411 specified on this property. 413 Conformance: This property can be specified zero or more times in 414 any iCalendar component. 416 Description: This property is used to specify formal categories or 417 classifications of the calendar component. The values are useful 418 in searching for a calendar component of a particular type and 419 category. 421 Within the "VEVENT", "VTODO", or "VJOURNAL" calendar components, 422 more than one formal category can be specified by using multiple 423 properties. 425 This categorization is distinct from the more informal "tagging" 426 of components provided by the existing CATEGORIES property. It is 427 expected that the value of the STRUCTURED-CATEGORY property will 428 reference an external resource which provides information about 429 the categorization. 431 In addition, a structured URI value allows for hierarchical 432 categorization of events. 434 Format Definition: 436 This property is defined by the following notation: 438 structured-category = "STRUCTURED-CATEGORY" structcatparam ":" uri CRLF 440 structcatparam = *( 441 ; 442 ; The following is OPTIONAL, 443 ; and MAY occur more than once. 444 ; 445 (";" other-param) 446 ; 447 ) 449 Example: 451 The following is an example of this property. It points to a server 452 acting as the source for the calendar object. 454 STRUCTURED-CATEGORY:http://example.com/event-types/sports 455 STRUCTURED-CATEGORY:http://example.com/event-types/arts/music 456 STRUCTURED-CATEGORY:http://example.com/task-types/delivery 458 7.2. Link 460 Property name: LINK 462 Purpose: This property provides a reference to external information 463 about a component. 465 Value type: URI, TEXT or REFERENCE 467 Property Parameters: Non-standard, reference type or format type 468 parameters can be specified on this property. 470 Conformance: This property MAY be specified in any iCalendar 471 component. 473 Description: When used in a component the value of this property 474 points to additional information related to the component. For 475 example, it may reference the originating web server. 477 Format Definition: 479 This property is defined by the following notation: 481 link = "LINK" linkparam ":" ( ":" uri ) / 482 ( 483 ";" "VALUE" "=" "REFERENCE" 484 ":" text 485 ) 486 CRLF 488 linkparam = *( 490 ; the following is MANDATORY 491 ; and MAY occur more than once 493 (";" relparam) / 495 ; the following are MANDATORY 496 ; but MUST NOT occur more than once 498 (";" fmttypeparam) / 499 (";" labelparam) / 500 ; labelparam is defined in ... 502 ; the following is OPTIONAL 503 ; and MAY occur more than once 505 (";" xparam) 507 ) 509 Example: 511 The following is an example of this property. It points to a server 512 acting as the source for the calendar object. 514 LINK;REL=SOURCE;LABEL=The Egg:http://example.com/events 516 7.3. Refid 518 Property name: REFID 520 Purpose: This property value acts as a key for associated iCalendar 521 entities. 523 Value type: TEXT 525 Property Parameters: Non-standard parameters can be specified on 526 this property. 528 Conformance: This property MAY be specified multiple times in any 529 iCalendar component. 531 Description: The value of this property is a text identifier that 532 allows associated components to be located or retrieved as a 533 whole. For example all of the events in a travel itinerary would 534 have the same REFID value. 536 Format Definition: 538 This property is defined by the following notation: 540 refid = "REFID" refidparam ":" text CRLF 542 refidparam = *( 544 ; the following is OPTIONAL 545 ; and MAY occur more than once 547 (";" xparam) 549 ) 551 Example: 553 The following is an example of this property. 555 REFID:itinerary-2014-11-17 557 8. Redefined RELATED-TO Property 558 8.1. RELATED-TO 560 Property name: RELATED-TO 562 Purpose: This property is used to represent a relationship or 563 reference between one calendar component and another. The 564 definition here extends the definition in Section 3.8.4.5. of 565 [RFC5545] by allowing URI values and a GAP parameter. 567 Value type: URI or TEXT 569 Property Parameters: Non-standard, reference type, gap, value or 570 format type parameters can be specified on this property. 572 Conformance: This property MAY be specified in any iCalendar 573 component. 575 Description: By default or when VALUE=UID is specified, the property 576 value consists of the persistent, globally unique identifier of 577 another calendar component. This value would be represented in a 578 calendar component by the "UID" property. 580 By default, the property value points to another calendar 581 component that has a PARENT relationship to the referencing 582 object. The "RELTYPE" property parameter is used to either 583 explicitly state the default PARENT relationship type to the 584 referenced calendar component or to override the default PARENT 585 relationship type and specify either a CHILD or SIBLING 586 relationship or a temporal relationship. 588 The PARENT relationship indicates that the calendar component is a 589 subordinate of the referenced calendar component. The CHILD 590 relationship indicates that the calendar component is a superior 591 of the referenced calendar component. The SIBLING relationship 592 indicates that the calendar component is a peer of the referenced 593 calendar component. 595 The FINISHTOSTART, FINISHTOFINISH, STARTTOFINISH or STARTTOSTART 596 relationships define temporal relationships as specified in the 597 reltype parameter definition. 599 Changes to a calendar component referenced by this property can 600 have an implicit impact on the related calendar component. For 601 example, if a group event changes its start or end date or time, 602 then the related, dependent events will need to have their start 603 and end dates changed in a corresponding way. Similarly, if a 604 PARENT calendar component is cancelled or deleted, then there is 605 an implied impact to the related CHILD calendar components. This 606 property is intended only to provide information on the 607 relationship of calendar components. It is up to the target 608 calendar system to maintain any property implications of this 609 relationship. 611 Format Definition: 613 This property is defined by the following notation: 615 related = "RELATED-TO" relparam ( ":" text ) / 616 ( 617 ";" "VALUE" "=" "UID" 618 ":" uid 619 ) 620 ( 621 ";" "VALUE" "=" "URI" 622 ":" uri 623 ) 624 CRLF 626 relparam = *( 627 ; 628 ; The following are OPTIONAL, 629 ; but MUST NOT occur more than once. 630 ; 631 (";" reltypeparam) / 632 (";" gapparam) / 633 ; 634 ; The following is OPTIONAL, 635 ; and MAY occur more than once. 636 ; 637 (";" other-param) 638 ; 639 ) 641 Example: 643 The following are examples of this property. 645 RELATED-TO:jsmith.part7.19960817T083000.xyzMail@example.com 647 RELATED-TO:19960401-080045-4000F192713-0052@example.com 649 RELATED-TO;VALUE=URI;RELTYPE=STARTTOFINISH: 650 http://example.com/caldav/user/jb/cal/ 651 19960401-080045-4000F192713.ics 653 9. Security Considerations 655 Applications using the LINK property need to be aware of the risks 656 entailed in using the URIs provided as values. See [RFC3986] for a 657 discussion of the security considerations relating to URIs. 659 The STRUCTURED-CATEGORY and redefined RELATED-TO property have the 660 same issues in that values may be URIs. 662 10. IANA Considerations 664 10.1. iCalendar Property Registrations 666 The following iCalendar property names have been added to the 667 iCalendar Properties Registry defined in Section 8.3.2 of [RFC5545] 669 +---------------------+---------+-------------+ 670 | Property | Status | Reference | 671 +---------------------+---------+-------------+ 672 | LINK | Current | Section 7.2 | 673 | REFID | Current | Section 7.3 | 674 | STRUCTURED-CATEGORY | Current | Section 7.1 | 675 +---------------------+---------+-------------+ 677 10.2. iCalendar Property Parameter Registrations 679 The following iCalendar property parameter names have been added to 680 the iCalendar Parameters Registry defined in Section 8.3.3 of 681 [RFC5545] 683 +---------------------+---------+-------------+ 684 | Parameter | Status | Reference | 685 +---------------------+---------+-------------+ 686 | REL | Current | Section 5.1 | 687 | GAP | Current | Section 5.2 | 688 | STRUCTURED-CATEGORY | Current | Section 7.1 | 689 +---------------------+---------+-------------+ 691 10.3. iCalendar Value Data Type Registrations 693 The following iCalendar property parameter names have been added to 694 the iCalendar Value Data Types Registry defined in Section 8.3.4 of 695 [RFC5545] 696 +-----------------+---------+-----------+ 697 | Value Data Type | Status | Reference | 698 +-----------------+---------+-----------+ 699 | UID | Current | Section 6 | 700 | REFERENCE | Current | Section 6 | 701 +-----------------+---------+-----------+ 703 10.4. iCalendar RELTYPE Value Registrations 705 The following iCalendar "RELTYPE" values have been added to the 706 iCalendar Relationship Types Registry defined in Section 8.3.8 of 707 [RFC5545] 709 +---------------------+---------+-----------+ 710 | Parameter | Status | Reference | 711 +---------------------+---------+-----------+ 712 | REL | Current | Section 4 | 713 | DEPENDS-ON | Current | Section 4 | 714 | REFID | Current | Section 4 | 715 | STRUCTURED-CATEGORY | Current | Section 4 | 716 | FINISHTOSTART | Current | Section 4 | 717 | FINISHTOFINISH | Current | Section 4 | 718 | STARTTOFINISH | Current | Section 4 | 719 | STARTTOSTART | Current | Section 4 | 720 +---------------------+---------+-----------+ 722 10.5. New Reference Type Registration 724 The following link relation values have been added to the Reference 725 Types Registry defined in Section 6.2.2 of [RFC5988] 727 +--------+---------+-------------+ 728 | Name | Status | Reference | 729 +--------+---------+-------------+ 730 | SOURCE | Current | Section 5.1 | 731 +--------+---------+-------------+ 733 11. Acknowledgements 735 The author would like to thank the members of the Calendaring and 736 Scheduling Consortium technical committees and the following 737 individuals for contributing their ideas, support and comments: 739 Adrian Apthorp, Cyrus Daboo, Marten Gajda 741 The authors would also like to thank the Calendaring and Scheduling 742 Consortium for advice with this specification. 744 12. Normative References 746 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 747 Requirement Levels", BCP 14, RFC 2119, March 1997. 749 [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, 750 January 2004. 752 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 753 Resource Identifier (URI): Generic Syntax", STD 66, RFC 754 3986, January 2005. 756 [RFC5545] Desruisseaux, B., "Internet Calendaring and Scheduling 757 Core Object Specification (iCalendar)", RFC 5545, 758 September 2009. 760 [RFC5988] Nottingham, M., "Web Linking", RFC 5988, October 2010. 762 [W3C.REC-xml-20060816] 763 Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E., and 764 F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fourth 765 Edition)", World Wide Web Consortium Recommendation REC- 766 xml-20060816, August 2006, 767 . 769 [W3C.WD-xptr-xpointer-20021219] 770 DeRose, S., Daniel, R., and E. Maler, "XPointer xpointer() 771 Scheme", World Wide Web Consortium WD WD-xptr-xpointer- 772 20021219, December 2002, 773 . 775 Appendix A. Change log 777 V04: 2014-11-18 MD 779 o Add 5545 registrations. 781 o Drop Q-name in favor of URI. 783 o Change REFID value type to text. 785 o Add STRUCTURED-CATEGORY property. 787 o Add STRUCTURED-CATEGORY relationship to RELATED-TO. 789 V03: 2014-09-21 MD 791 o Added Q-name specification. 793 o Change RELATED-ID to REFID and change its value type to Q-name. 795 o Add REFID relationship to RELATED-TO. 797 V02: 2013-11-22 MD 799 o Added more description to GAP 801 V01: 2013-09-26 MD 803 o Removed "Improved" from title 805 o Fixed typos and examples 807 o Removed gap param from link 809 2013-06-02 MD Initial version 811 Author's Address 813 Michael Douglass 814 Rensselaer Polytechnic Institute 815 110 8th Street 816 Troy, NY 12180 817 USA 819 Email: douglm@rpi.edu 820 URI: http://www.rpi.edu/