idnits 2.17.00 (12 Aug 2021) /tmp/idnits11069/draft-ietf-calext-ical-relations-09.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- ** There are 3 instances of too long lines in the document, the longest one being 6 characters in excess of 72. -- The draft header indicates that this document updates RFC5545, but the abstract doesn't seem to mention this, which it should. Miscellaneous warnings: ---------------------------------------------------------------------------- == The document seems to lack the recommended RFC 2119 boilerplate, even if it appears to use RFC 2119 keywords -- however, there's a paragraph with a matching beginning. Boilerplate error? (The document does seem to have the reference to RFC 2119 which the ID-Checklist requires). (Using the creation date from RFC5545, updated by this document, for RFC5378 checks: 2005-10-26) -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (23 January 2022) is 112 days in the past. Is this intentional? -- Found something which looks like a code comment -- if you have code sections in the document, please surround them with '' and '' lines. Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Looks like a reference, but probably isn't: '1' on line 545 Summary: 1 error (**), 0 flaws (~~), 1 warning (==), 5 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group M. Douglass 3 Internet-Draft Bedework 4 Updates: 5545 (if approved) 23 January 2022 5 Intended status: Standards Track 6 Expires: 27 July 2022 8 Support for iCalendar Relationships 9 draft-ietf-calext-ical-relations-09 11 Abstract 13 This specification updates the iCalendar RELATED-TO property by 14 adding new relation types and introduces new iCalendar properties 15 LINK, CONCEPT and REFID to allow better linking and grouping of 16 iCalendar components and related data. 18 Status of This Memo 20 This Internet-Draft is submitted in full conformance with the 21 provisions of BCP 78 and BCP 79. 23 Internet-Drafts are working documents of the Internet Engineering 24 Task Force (IETF). Note that other groups may also distribute 25 working documents as Internet-Drafts. The list of current Internet- 26 Drafts is at https://datatracker.ietf.org/drafts/current/. 28 Internet-Drafts are draft documents valid for a maximum of six months 29 and may be updated, replaced, or obsoleted by other documents at any 30 time. It is inappropriate to use Internet-Drafts as reference 31 material or to cite them other than as "work in progress." 33 This Internet-Draft will expire on 27 July 2022. 35 Copyright Notice 37 Copyright (c) 2022 IETF Trust and the persons identified as the 38 document authors. All rights reserved. 40 This document is subject to BCP 78 and the IETF Trust's Legal 41 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 42 license-info) in effect on the date of publication of this document. 43 Please review these documents carefully, as they describe your rights 44 and restrictions with respect to this document. Code Components 45 extracted from this document must include Revised BSD License text as 46 described in Section 4.e of the Trust Legal Provisions and are 47 provided without warranty as described in the Revised 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. Concept relationships . . . . . . . . . . . . . . . . . . 3 55 1.4. Linked relationships . . . . . . . . . . . . . . . . . . 4 56 1.5. Caching and offline use . . . . . . . . . . . . . . . . . 5 57 1.6. Conventions Used in This Document . . . . . . . . . . . . 5 58 2. Reference Types . . . . . . . . . . . . . . . . . . . . . . . 5 59 3. Link Relation Types . . . . . . . . . . . . . . . . . . . . . 6 60 4. New temporal RELTYPE Parameter values . . . . . . . . . . . . 6 61 5. Additional New RELTYPE Parameter Values . . . . . . . . . . . 7 62 6. New Property Parameters . . . . . . . . . . . . . . . . . . . 8 63 6.1. Link Relation . . . . . . . . . . . . . . . . . . . . . . 8 64 6.2. Gap . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 65 7. New Value Data Types . . . . . . . . . . . . . . . . . . . . 9 66 8. New Properties . . . . . . . . . . . . . . . . . . . . . . . 9 67 8.1. Concept . . . . . . . . . . . . . . . . . . . . . . . . . 9 68 8.2. Link . . . . . . . . . . . . . . . . . . . . . . . . . . 10 69 8.3. Refid . . . . . . . . . . . . . . . . . . . . . . . . . . 12 70 9. Updates to RFC 5545 . . . . . . . . . . . . . . . . . . . . . 13 71 9.1. RELATED-TO . . . . . . . . . . . . . . . . . . . . . . . 13 72 10. Security Considerations . . . . . . . . . . . . . . . . . . . 15 73 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 74 11.1. iCalendar Property Registrations . . . . . . . . . . . . 16 75 11.2. iCalendar Property Parameter Registrations . . . . . . . 16 76 11.3. iCalendar Value Data Type Registrations . . . . . . . . 16 77 11.4. iCalendar RELTYPE Value Registrations . . . . . . . . . 17 78 11.5. New Reference Type Registration . . . . . . . . . . . . 17 79 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 18 80 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 81 13.1. Informative References . . . . . . . . . . . . . . . . . 18 82 13.2. Normative References . . . . . . . . . . . . . . . . . . 18 83 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 19 85 1. Introduction 87 iCalendar entities defined in [RFC5545] often need to be related to 88 each other or to associated meta-data. The specifications below 89 support relationships of the following forms: 91 Structured iCalendar: iCalendar entities can be related to each 92 other in some structured way, for example as parent, sibling, 93 before, after. 95 Grouped iCalendar: iCalendar entities can be related to each other 96 as a group. CATEGORIES are often used for this purpose but are 97 problematic for application developers due to their lack of 98 consistency and use as a free-form tag. 100 Linked: Entities can be linked to other entities such as vcards 101 through a URI and associated REL and FMTTYPE parameters. 103 1.1. Structured iCalendar relationships 105 The iCalendar [RFC5545] RELATED-TO property has no support for 106 temporal relationships as used by standard project management tools. 108 The RELTYPE parameter is extended to take new values defining 109 temporal relationships, a GAP parameter is defined to provide lead 110 and lag values, and RELATED-TO is extended to allow URI values. 111 These changes allow the RELATED-TO property to define a richer set of 112 relationships useful for project management. 114 1.2. Grouped iCalendar relationships 116 This specification defines a new REFID property which allows 117 arbitrary groups of entities to be associated with the same key 118 value. 120 REFID is used to identify a key allowing the association of 121 components that are related to the same object and retrieval of a 122 component based on this key. Two examples of how this may be used 123 are to identify the tasks associated with a given project without 124 having to communicate the task structure of the project, and to group 125 all tasks associated to a specific package in a package delivery 126 system. 128 As such, the presence of a REFID property imparts no meaning to the 129 component. It is merely a key to allow retrieval. This is distinct 130 from categorisation which, while allowing grouping also adds meaning 131 to the component to which it is attached. 133 1.3. Concept relationships 135 The name CONCEPT is used by the Simple Knowledge Organization System 136 defined in [W3C.REC-skos-reference-20090818]. The term "concept" 137 more accurately defines what we often mean by a category. It's not 138 the text string that is important but the meaning attached to it. 139 For example, the term "football" can mean very different sports. 141 The introduction of CONCEPT allows a more structured approach to 142 categorization, with the possibility of namespaced and path-like 143 values. Unlike REFID the CONCEPT property imparts some meaning. It 144 is assumed that the value of this property will reference a well 145 defined category. 147 The current [RFC5545] CATEGORY property is used as a free form 148 'tagging' field. As such it is difficult to establish formal 149 relationships between components based on their category. 151 Rather than attempt to add semantics to the CATEGORY property it 152 seems best to continue its usage as an informal tag and establish a 153 new CONCEPT property with more constraints. 155 1.4. Linked relationships 157 The currently existing iCalendar standard [RFC5545] lacks a general 158 purpose method for referencing additional, external information 159 relating to calendar components. 161 This document proposes a method for referencing typed external 162 information that can provide additional information about an 163 iCalendar component. This new LINK property is closely aligned to 164 the LINK header defined in [RFC8288] 166 The LINK property defines a typed reference or relation to external 167 meta-data or related resources. By providing type and format 168 information as parameters, clients and servers are able to discover 169 interesting references and make use of them, perhaps for indexing or 170 the presentation of interesting links for the user. 172 It is also often necessary to reference calendar components in other 173 collections. For example, a VEVENT might refer to a VTODO from which 174 it was derived. The PARENT, SIBLING and CHILD relationships defined 175 for the RELATED-TO property only allow for a UID which is inadequate 176 for many purposes. Allowing other value types for those 177 relationships may help but would cause backward compatibility issues. 178 The LINK property can link components in different collections or 179 even on different servers. 181 When publishing events it is useful to be able to refer back to the 182 source of that information. The actual event may have been consumed 183 from a feed or an ics file on a web site. A LINK property can 184 provide a reference to the originator of the event. 186 Beyond the need to relate elements temporally, project management 187 tools often need to be able to specify the relationships between the 188 various events and tasks which make up a project. The LINK property 189 provides such a mechanism. 191 The LINK property MUST NOT be treated as just another attachment. 192 The ATTACH property defined in [RFC5545] is being extended to handle 193 server-side management and stripping of inline data. Clients may 194 choose to handle attachments differently from the LINK property as 195 they are often an integral part of the message - for example, the 196 agenda. 198 For more information on managed attachments see [RFC8607] 200 1.5. Caching and offline use 202 To facilitate offline display the link type may identify important 203 pieces of data which should be downloaded in advance. 205 In general, the calendar entity should be self explanatory without 206 the need to download referenced meta-data such as a web page. 208 1.6. Conventions Used in This Document 210 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 211 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY" and 212 "OPTIONAL" in this document are to be interpreted as described in BCP 213 14 [RFC2119] [RFC8174] when, and only when, they appear in all 214 capitals, as shown here. 216 2. Reference Types 218 The actual reference value can take three forms specified by the type 219 parameter 221 URI: The default type. This is a URI referring to the target. 223 UID: This allows for linking within a single collection and the 224 value MUST be another component within that collection. 226 REFERENCE: In an XML environment it may be necessary to refer to a 227 fragment of an external XML artifact. This value is a URI with an 228 XPointer anchor value. The XPointer is defined in 229 [W3C.WD-xptr-xpointer-20021219] and it's use as an anchor is 230 defined in [W3C.REC-xptr-framework-20030325] 232 3. Link Relation Types 234 [RFC8288] defines two forms of relation type: registered and 235 extension. Registered relation types are added to the Link Relations 236 registry as specified in Section 2.1.1 of [RFC8288]. Extension 237 relation types, defined in Section 2.1.2 of [RFC8288], are specified 238 as unique URIs that are not registered in the registry. 240 The relation types defined in Section 6.1 will be registered with 241 IANA in accordance with the specifications in [RFC8288]. 243 4. New temporal RELTYPE Parameter values 245 This section defines the usual temporal relationships for use with 246 the RELTYPE parameter defined in Section 3.2.15 of [RFC5545]: 247 FINISHTOSTART, FINISHTOFINISH, STARTTOFINISH or STARTTOSTART. 249 The [RFC5545] RELATED-TO property with one or more of these temporal 250 relationships will be present in the predecessor entity and will 251 refer to the successor entity. 253 The GAP parameter (see Section 6.2) specifies the lead or lag time 254 between the predecessor and the successor. In the description of 255 each temporal relationship below we refer to Task-A, which contains 256 and controls the relationship, and Task-B the target of the 257 relationship. 259 RELTYPE=FINISHTOSTART: Task-B cannot start until Task-A finishes. 260 For example, when sanding is complete, painting can begin. 262 ============ 263 | Task-A |--+ 264 ============ | 265 | 266 V 267 ============ 268 | Task-B | 269 ============ 271 Figure 1: Finish to start relationship 273 RELTYPE=FINISHTOFINISH: Task-B can only be completed after Task-A is 274 finished. The related tasks may run in parallel before 275 completion. 277 For example, if the goal is to prepare a meal, we start the 278 potatoes, then the meat then the peas but they should all be 279 cooked at the same time. 281 ================== 282 | Task-A |--+ 283 ================== | 284 | 285 ============ | 286 | Task-B |<-+ 287 ============ 289 Figure 2: Finish to finish relationship 291 RELTYPE=STARTTOFINISH: The start of Task-A (which occurs after Task- 292 B) controls the finish of Task-B. For example, ticket sales 293 (Task-B) end when the game starts (Task-A). 295 ============ 296 +--| Task-A | 297 | ============ 298 | 299 ============ | 300 | Task-B |<-+ 301 ============ 303 Figure 3: Start to finish relationship 305 RELTYPE=STARTTOSTART: The start of Task-A triggers the start of 306 Task-B, that is Task-B can start anytime after Task-A starts. 308 ============ 309 +--| Task-A | 310 | ============ 311 | 312 | ============ 313 +->| Task-B | 314 ============ 316 Figure 4: Start to start relationship 318 5. Additional New RELTYPE Parameter Values 320 This section defines the additional relationships below: 322 RELTYPE=FIRST: Indicates that the referenced calendar component is 323 the first in a series the referenced calendar component is part 324 of. 326 RELTYPE=DEPENDS-ON: Indicates that the current calendar component 327 depends on the referenced calendar component in some manner. For 328 example a task may be blocked waiting on the other, referenced, 329 task. 331 RELTYPE=REFID: Establishes a reference from the current component to 332 components with a REFID property which matches the value given in 333 the associated RELATED-TO property. 335 RELTYPE=CONCEPT: Establishes a reference from the current component 336 to components with a CONCEPT property which matches the value 337 given in the associated RELATED-TO property. 339 6. New Property Parameters 341 6.1. Link Relation 343 Parameter name: LINKREL 345 Purpose: To specify the relationship of data referenced by a LINK 346 property. 348 Format Definition: This parameter is defined by the following 349 notation: 351 linkrelparam = "LINKREL" "=" 352 ("SOURCE" ; Link to source of this component 353 / DQUOTE uri DQUOTE 354 / iana-token) ; Other IANA registered type 356 Description: This parameter MUST be specified on all LINK 357 properties, and defines the type of reference. This allows 358 programs consuming this data to automatically scan for references 359 they support. There is no default relation type. 361 In addition to the values defined here any value defined in 362 [RFC8288] may be used. However these uses SHOULD be documented in 363 an RFC updating both [RFC5545] and [RFC8288] 365 LINKREL=SOURCE: identifies the source of the event information. 367 Registration: These relation types are registered in [RFC8288] 369 6.2. Gap 371 Parameter name: GAP 373 Purpose: To specify the length of the gap, positive or negative, 374 between two temporaly related components. 376 Format Definition: This parameter is defined by the following 377 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 7. 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 405 references an associated XML artifact and is a URI with an 406 XPointer anchor value. The XPointer is defined in 407 [W3C.WD-xptr-xpointer-20021219] and it's use as an anchor is 408 defined in [W3C.REC-xptr-framework-20030325]. 410 8. New Properties 412 8.1. Concept 414 Property name: CONCEPT 416 Purpose: This property defines the formal categories for a calendar 417 component. 419 Value type: URI 421 Property Parameters: IANA, and non-standard parameters can be 422 specified on this property. 424 Conformance: This property can be specified zero or more times in 425 any iCalendar component. 427 Description: This property is used to specify formal categories or 428 classifications of the calendar component. The values are useful 429 in searching for a calendar component of a particular type and 430 category. 432 Within the "VEVENT", "VTODO", or "VJOURNAL" calendar components, 433 more than one formal category can be specified by using multiple 434 CONCEPT properties. 436 This categorization is distinct from the more informal "tagging" 437 of components provided by the existing CATEGORIES property. It is 438 expected that the value of the CONCEPT property will reference an 439 external resource which provides information about the 440 categorization. 442 In addition, a structured URI value allows for hierarchical 443 categorization of events. 445 Possible category resources are the various proprietary systems, 446 for example Library of Congress, or an open source of 447 categorisation data. 449 Format Definition: This property is defined by the following 450 notation: 452 concept = "CONCEPT" conceptparam ":" 453 uri CRLF 455 conceptparam = *(";" other-param) 457 Example: The following is an example of this property. It points to 458 a server acting as the source for the calendar object. 460 CONCEPT:http://example.com/event-types/arts/music 462 8.2. Link 464 Property name: LINK 466 Purpose: This property provides a reference to external information 467 related to a component. 469 Value type: URI, TEXT or REFERENCE 470 Property Parameters: The VALUE parameter is required. Non-standard, 471 reference type or format type parameters can also be specified on 472 this property. The LABEL parameter is defined in [RFC7986] 474 Conformance: This property can be specified zero or more times in 475 any iCalendar component. 477 Description: When used in a component the value of this property 478 points to additional information related to the component. For 479 example, it may reference the originating web server. 481 Format Definition: This property is defined by the following 482 notation: 484 link = "LINK" linkparam ":" 485 ( uri / ; for VALUE=REFERENCE 486 uri / ; for VALUE=URI 487 text ) ; for VALUE=TEXT 488 CRLF 490 linkparam = ; the elements herein may appear in any order, 491 ; and the order is not significant. 493 (";" "VALUE" "=" ("REFERENCE" / 494 "URI" / 495 "TEXT")) 496 1*(";" linkrelparam) 497 (";" fmttypeparam) 498 (";" labelparam) 499 (";" langparam) 500 *(";" other-param) 502 This property is a serialisation of the model in [RFC8288], where 503 the link target is carried in the property value, the link context 504 is the containing calendar entity, and the link relation type and 505 any target attributes are carried in iCalendar property 506 parameters. 508 The LINK property parameters map to [RFC8288] attributes as 509 follows: 511 LABEL: Maps to the "title" attribute defined in section 3.4.1 of 512 [RFC8288]. 514 LANG: Maps to the "hreflang" attribute defined in section 3.4.1 515 of [RFC8288]. 517 LINKREL: Maps to the link relation type defined in section 2.1 of 518 [RFC8288]. 520 FMTTYPE: Maps to the "type" attribute defined in section 3.4.1 of 521 [RFC8288]. 523 There is no mapping for [RFC8288] "title*", "anchor", "rev" or 524 "media". 526 Example: The following is an example of this property which provides 527 a reference to the source for the calendar object. 529 LINK;LINKREL=SOURCE;LABEL=Venue;VALUE=URI:http://example.com/events 531 Example: The following is an example of this property which provides 532 a reference to an entity from which this one was derived. The 533 link relation is a vendor defined value 535 LINK;LINKREL="https://example.com/linkrel/derivedFrom";VALUE=URI: 536 http://example.com/tasks/01234567-abcd1234.ics 538 Example: The following is an example of this property which provides 539 a reference to a fragment of an XML document. The link relation 540 is a vendor defined value 542 LINK;LINKREL="https://example.com/linkrel/costStructure"; 543 VALUE=REFERENCE: 544 http://example.com/xmlDocs/bidFramework.xml 545 #xpointer(descendant::CostStruc/range-to(following::CostStrucEND[1])) 547 8.3. Refid 549 Property name: REFID 551 Purpose: This property value acts as a key for associated iCalendar 552 entities. 554 Value type: TEXT 556 Property Parameters: Non-standard parameters can be specified on 557 this property. 559 Conformance: This property can be specified zero or more times in 560 any iCalendar component. 562 Description: The value of this property is free-form text that 563 creates an identifier for associated components. All components 564 that use the same REFID value are associated through that value 565 and can be located or retrieved as a group. For example, all of 566 the events in a travel itinerary would have the same REFID value, 567 so as to be grouped together. 569 Format Definition: This property is defined by the following 570 notation: 572 refid = "REFID" refidparam ":" text CRLF 574 refidparam = *(";" other-param) 576 The current link registry 578 Example: The following is an example of this property. 580 REFID:itinerary-2014-11-17 582 9. Updates to RFC 5545 584 This specification updates the RELATED-TO property defined in 585 Section 3.8.4.5 of [RFC5545]. 587 The RELTYPE parameter is extended to take new values defining 588 temporal relationships, a GAP parameter is defined to provide lead 589 and lag values, and RELATED-TO is extended to allow URI values. 590 These changes allow the RELATED-TO property to define a richer set of 591 relationships useful for project management. 593 9.1. RELATED-TO 595 Property name: RELATED-TO 597 Purpose: This property is used to represent a relationship or 598 reference between one calendar component and another. The 599 definition here extends the definition in Section 3.8.4.5 of 600 [RFC5545] by allowing URI or UID values and a GAP parameter. 602 Value type: URI, UID or TEXT 604 Property Parameters: Relationship type, IANA and non-standard 605 property parameters can be specified on this property. 607 Conformance: This property MAY be specified in any iCalendar 608 component. 610 Description: By default or when VALUE=UID is specified, the property 611 value consists of the persistent, globally unique identifier of 612 another calendar component. This value would be represented in a 613 calendar component by the "UID" property. 615 By default, the property value points to another calendar 616 component that has a PARENT relationship to the referencing 617 object. The "RELTYPE" property parameter is used to either 618 explicitly state the default PARENT relationship type to the 619 referenced calendar component or to override the default PARENT 620 relationship type and specify either a CHILD or SIBLING 621 relationship or a temporal relationship. 623 The PARENT relationship indicates that the calendar component is a 624 subordinate of the referenced calendar component. The CHILD 625 relationship indicates that the calendar component is a superior 626 of the referenced calendar component. The SIBLING relationship 627 indicates that the calendar component is a peer of the referenced 628 calendar component. 630 To preserve backwards compatibility the value type MUST be UID 631 when the PARENT, SIBLING or CHILD relationships are specified. 633 The FINISHTOSTART, FINISHTOFINISH, STARTTOFINISH or STARTTOSTART 634 relationships define temporal relationships as specified in the 635 reltype parameter definition. 637 Changes to a calendar component referenced by this property can 638 have an implicit impact on the related calendar component. For 639 example, if a group event changes its start or end date or time, 640 then the related, dependent events will need to have their start 641 and end dates changed in a corresponding way. Similarly, if a 642 PARENT calendar component is cancelled or deleted, then there is 643 an implied impact to the related CHILD calendar components. This 644 property is intended only to provide information on the 645 relationship of calendar components. It is up to the target 646 calendar system to maintain any property implications of this 647 relationship. 649 Format Definition: This property is defined by the following 650 notation: 652 related = "RELATED-TO" relparam ":" 653 ( uid / ; for VALUE=UID 654 uri / ; for VALUE=URI 655 text ) ; for VALUE=TEXT or default 656 CRLF 658 relparam = ; the elements herein may appear in any order, 659 ; and the order is not significant. 660 [";" "VALUE" "=" ("UID" / 661 "URI" / 662 "TEXT")] 663 [";" reltypeparam] 664 [";" gapparam] 665 *(";" other-param) 667 Example: The following are examples of this property. 669 RELATED-TO:jsmith.part7.19960817T083000.xyzMail@example.com 671 RELATED-TO:19960401-080045-4000F192713-0052@example.com 673 RELATED-TO;VALUE=URI;RELTYPE=STARTTOFINISH: 674 http://example.com/caldav/user/jb/cal/ 675 19960401-080045-4000F192713.ics 677 10. Security Considerations 679 Applications using the LINK property need to be aware of the risks 680 entailed in using the URIs provided as values. See section 7 of 681 [RFC3986] for a discussion of the security considerations relating to 682 URIs. 684 In particular note section 7.1 "Reliability and Consistency" of 685 [RFC3986] which points out the lack of a stability guarantee for 686 referenced resources. 688 When the value is a REFERENCE type the targeted data is an XML 689 document or portion thereof. Consumers need to be aware of the 690 security issues related to XML processing - in particular those 691 related to XML entities. See [RFC4918] - Section 20.6. Additionally 692 note that the reference may be invalid or become so over time. 694 The CONCEPT and redefined RELATED-TO property have the same issues in 695 that values may be URIs. 697 11. IANA Considerations 699 11.1. iCalendar Property Registrations 701 The following iCalendar property names have been added to the 702 iCalendar Properties Registry defined in Section 8.3.2 of [RFC5545] 703 IANA has also added a reference to this document where the properties 704 originally defined in [RFC5545] have been updated by this document. 706 +============+=========+========================+ 707 | Property | Status | Reference | 708 +============+=========+========================+ 709 | CONCEPT | Current | Section 8.1 | 710 +------------+---------+------------------------+ 711 | LINK | Current | Section 8.2 | 712 +------------+---------+------------------------+ 713 | REFID | Current | Section 8.3 | 714 +------------+---------+------------------------+ 715 | RELATED-TO | Current | [RFC5545], Section 9.1 | 716 +------------+---------+------------------------+ 718 Table 1 720 11.2. iCalendar Property Parameter Registrations 722 The following iCalendar property parameter names have been added to 723 the iCalendar Parameters Registry defined in Section 8.3.3 of 724 [RFC5545] 726 +===========+=========+=============+ 727 | Parameter | Status | Reference | 728 +===========+=========+=============+ 729 | GAP | Current | Section 6.2 | 730 +-----------+---------+-------------+ 731 | LINKREL | Current | Section 6.1 | 732 +-----------+---------+-------------+ 734 Table 2 736 11.3. iCalendar Value Data Type Registrations 738 The following iCalendar property parameter names have been added to 739 the iCalendar Value Data Types Registry defined in Section 8.3.4 of 740 [RFC5545] 741 +=================+=========+===========+ 742 | Value Data Type | Status | Reference | 743 +=================+=========+===========+ 744 | REFERENCE | Current | Section 7 | 745 +-----------------+---------+-----------+ 746 | UID | Current | Section 7 | 747 +-----------------+---------+-----------+ 749 Table 3 751 11.4. iCalendar RELTYPE Value Registrations 753 The following iCalendar "RELTYPE" values have been added to the 754 iCalendar Relationship Types Registry defined in Section 8.3.8 of 755 [RFC5545] 757 +===================+=========+===========+ 758 | Relationship Type | Status | Reference | 759 +===================+=========+===========+ 760 | CONCEPT | Current | Section 5 | 761 +-------------------+---------+-----------+ 762 | DEPENDS-ON | Current | Section 5 | 763 +-------------------+---------+-----------+ 764 | FINISHTOFINISH | Current | Section 4 | 765 +-------------------+---------+-----------+ 766 | FINISHTOSTART | Current | Section 4 | 767 +-------------------+---------+-----------+ 768 | FIRST | Current | Section 5 | 769 +-------------------+---------+-----------+ 770 | REFID | Current | Section 5 | 771 +-------------------+---------+-----------+ 772 | STARTTOFINISH | Current | Section 4 | 773 +-------------------+---------+-----------+ 774 | STARTTOSTART | Current | Section 4 | 775 +-------------------+---------+-----------+ 777 Table 4 779 11.5. New Reference Type Registration 781 The following link relation values have been added to the Reference 782 Types Registry defined in Section 6.2.2 of [RFC8288] 783 +========+=========+=============+ 784 | Name | Status | Reference | 785 +========+=========+=============+ 786 | SOURCE | Current | Section 6.1 | 787 +--------+---------+-------------+ 789 Table 5 791 12. Acknowledgements 793 The author would like to thank the members of the Calendaring and 794 Scheduling Consortium technical committees and the following 795 individuals for contributing their ideas, support and comments: 797 Adrian Apthorp, Cyrus Daboo, Marten Gajda, Ken Murchison 799 The author would also like to thank CalConnect, the Calendaring and 800 Scheduling Consortium for advice with this specification. 802 13. References 804 13.1. Informative References 806 [RFC8607] Daboo, C., Quillaud, A., and K. Murchison, Ed., 807 "Calendaring Extensions to WebDAV (CalDAV): Managed 808 Attachments", RFC 8607, DOI 10.17487/RFC8607, June 2019, 809 . 811 13.2. Normative References 813 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 814 Requirement Levels", BCP 14, RFC 2119, 815 DOI 10.17487/RFC2119, March 1997, 816 . 818 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 819 Resource Identifier (URI): Generic Syntax", STD 66, 820 RFC 3986, DOI 10.17487/RFC3986, January 2005, 821 . 823 [RFC4918] Dusseault, L., Ed., "HTTP Extensions for Web Distributed 824 Authoring and Versioning (WebDAV)", RFC 4918, 825 DOI 10.17487/RFC4918, June 2007, 826 . 828 [RFC5545] Desruisseaux, B., Ed., "Internet Calendaring and 829 Scheduling Core Object Specification (iCalendar)", 830 RFC 5545, DOI 10.17487/RFC5545, September 2009, 831 . 833 [RFC7986] Daboo, C., "New Properties for iCalendar", RFC 7986, 834 DOI 10.17487/RFC7986, October 2016, 835 . 837 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 838 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 839 May 2017, . 841 [RFC8288] Nottingham, M., "Web Linking", RFC 8288, 842 DOI 10.17487/RFC8288, October 2017, 843 . 845 [W3C.REC-skos-reference-20090818] 846 Miles, A. and S. Bechhofer, "SKOS Simple Knowledge 847 Organization System Reference", World Wide Web Consortium 848 Recommendation REC-skos-reference-20090818, 18 August 849 2009, 850 . 852 [W3C.REC-xptr-framework-20030325] 853 Grosso, P., Maler, E., Marsh, J., and N. Walsh, "XPointer 854 Framework", World Wide Web Consortium Recommendation REC- 855 xptr-framework-20030325, 25 March 2003, 856 . 858 [W3C.WD-xptr-xpointer-20021219] 859 DeRose, S., Daniel, R., and E. Maler, "XPointer xpointer() 860 Scheme", World Wide Web Consortium WD WD-xptr-xpointer- 861 20021219, 19 December 2002, 862 . 864 Author's Address 866 Michael Douglass 867 Bedework 868 226 3rd Street 869 Troy, NY 12180 870 United States of America 872 Email: mdouglass@bedework.com 873 URI: http://bedework.com