| Network Working Group | M. Douglass |
| Internet-Draft | RPI |
| Intended status: Standards Track | January 07, 2014 |
| Expires: July 11, 2014 |
Support for Icalendar Relationships
draft-douglass-ical-relations-02
This specification updates RELATED-TO and introduces new iCalendar properties LINK and RELATED-ID to allow better linking and grouping of iCalendar components and related data.
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Icalendar entities often need to be related to each other or to associated meta-data. These relationships can take the following forms
The currently existing iCalendar [RFC5545] RELATED-TO property has no support for temporal relationships as used by standard project management tools.
The RELTYPE parameter is extended to take new values defining temporal relationships, a GAP parameter is defined to provide lead and lag values and RELATED-TO is extended to allow URI values. These changes allows the RELATED-TO property to define a richer set of relationships useful for project management.
This specification defines a new RELATED-ID property which allows arbitrary groups of entities to be created. This provides a more structured approach to categorization, allowing namespaced values and providing some assurance for applications that these groupings will be preserved.
The currently existing iCalendar standard [RFC5545] lacks a general purpose method for referencing additional, external information relating to calendar components.
This document proposes a method for referencing typed external information that can provide additional information about an iCalendar component. This new LINK property is closely aligned to the LINK header defined in [RFC5988]
The LINK property defines a typed reference or relation to external meta-data or related resources. By providing type and format information as parameters, clients and servers are able to discover interesting references and make use of them, perhaps for indexing or the presentation of interesting links for the user.
It is often necessary to relate calendar components. The current RELATED-TO property only allows for a UID which is inadequate for many purposes. Allowing other types may help but might raise a number of backward compatibility issues. The link property can link components in different collections or even on different servers.
When publishing events it is useful to be able to refer back to the source of that information. The actual event may have been consumed from a feed or an ics file on a web site. A LINK property can provide a reference to the originator of the event.
Beyond the need to relate elements temporally, project management tools often need to be able to specify the relationships between the various events and tasks which make up a project. The LINK property provides such a mechanism.
A section about offline use. Use the link type to identify important pieces of data.
Client may load subset of data due to e.g. a time-range query. Should it pull in all the related data?
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].
The actual reference value can take three forms specified by the type parameter
[RFC5988] defines two form of relation types, registered and extension. Registered relation types are added to a registry defined by [RFC5988] while extension relation types are specified as unique unregistered URIs, (at least unregistered in the [RFC5988] registry).
The relation types defined here will be registered with IANA in accordance with the specifications in [RFC5988].
Relationship parameter type values are defined in section 3.2.15. of [RFC5545]. This specification redefines that type to include the new temporal relationship values FINISHTOSTART, FINISHTOFINISH, STARTTOFINISH and STARTTOSTART. It also adds the DEPENDS-ON value to provide a link to an component upon which the current component depends.
This property parameter is defined by the following notation:
reltypeparam = "RELTYPE" "="
("PARENT" ; Parent relationship - Default
/ "CHILD" ; Child relationship
/ "SIBLING" ; Sibling relationship
/ "DEPENDS-ON" ; refers to previous task
/ "FINISHTOSTART" ; Temporal relationship
/ "FINISHTOFINISH" ; Temporal relationship
/ "STARTTOFINISH" ; Temporal relationship
/ "STARTTOSTART" ; Temporal relationship
/ iana-token ; Some other IANA-registered
; iCalendar relationship type
/ x-name) ; A non-standard, experimental
; relationship type
============
| Task-A |--+
============ |
|
V
============
| Task-B |
============
Figure 1: Finish to start relationship
============
| Task-A |--+
============ |
|
============ |
| Task-B |<-+
============
Figure 2: Finish to finish relationship
============
+--| Task-A |
| ============
|
============ |
| Task-B |<-+
============
Figure 3: Start to finish relationship
============
+--| Task-A |
| ============
|
| ============
+->| Task-B |
============
Figure 4: Start to start relationship
This parameter is defined by the following notation:
relparam = "REL" "="
("SOURCE" ; Link to source of this component
/ DQUOTE uri DQUOTE
/ x-name ; Experimental reference type
/ iana-token) ; Other IANA registered type
This parameter is defined by the following notation:
gapparam = "GAP" "=" dur-value
This parameter is defined by the following notation:
titleparam = "TITLE" "=" text
This specification defines a new value to be used with the VALUE property parameter:
This property is defined by the following notation:
link = "LINK" linkparam ":" ( ":" uri ) /
(
";" "VALUE" "=" "REFERENCE"
":" text
)
CRLF
linkparam = *(
; the following is MANDATORY
; and MAY occur more than once
(";" relparam) /
; the following are MANDATORY
; but MUST NOT occur more than once
(";" fmttypeparam) /
(";" titleparam) /
; the following is OPTIONAL
; and MAY occur more than once
(";" xparam)
)
The following is an example of this property. It points to a server acting as the source for the calendar object.
LINK;REL=SOURCE;TITLE=The Egg:
http://example.com/events
This property is defined by the following notation:
related-id = "RELATED-ID" relidparam ":" text CRLF
relidparam = *(
; the following is OPTIONAL
; and MAY occur more than once
(";" xparam)
)
The following is an example of this property. It defines an id in the org.calconnect namespace.
RELATED-ID:{org.calconnect.project}Main-Project
This property is defined by the following notation:
related = "RELATED-TO" relparam ( ":" text ) /
(
";" "VALUE" "=" "UID"
":" uid
)
(
";" "VALUE" "=" "URI"
":" uri
)
CRLF
relparam = *(
;
; The following are OPTIONAL,
; but MUST NOT occur more than once.
;
(";" reltypeparam) /
(";" gapparam) /
;
; The following is OPTIONAL,
; and MAY occur more than once.
;
(";" other-param)
;
)
The following are examples of this property.
RELATED-TO:jsmith.part7.19960817T083000.xyzMail@example.com
RELATED-TO:19960401-080045-4000F192713-0052@example.com
RELATED-TO;VALUE=URI;RELTYPE=STARTTOFINISH:
http://example.com/caldav/user/jb/cal/
19960401-080045-4000F192713.ics
Applications using the LINK property need to be aware of the risks entailed in using the URIs provided as values. See [RFC3986] for a discussion of the security considerations relating to URIs.
The author would like to thank the members of the Calendaring and Scheduling Consortium technical committees and the following individuals for contributing their ideas, support and comments:
Adrian Apthorp, Cyrus Daboo, Marten Gajda
The authors would also like to thank the Calendaring and Scheduling Consortium for advice with this specification.
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. |
| [RFC5545] | Desruisseaux, B., "Internet Calendaring and Scheduling Core Object Specification (iCalendar)", RFC 5545, September 2009. |
| [RFC5988] | Nottingham, M., "Web Linking", RFC 5988, October 2010. |
| [RFC3688] | Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, January 2004. |
| [RFC3986] | Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005. |
| [W3C.REC-xml-20060816] | Yergeau, F., Paoli, J., Bray, T., Maler, E. and C. Sperberg-McQueen, "Extensible Markup Language (XML) 1.0 (Fourth Edition)", World Wide Web Consortium FirstEdition REC-xml-20060816, August 2006. |
| [W3C.WD-xptr-xpointer-20021219] | DeRose, S., Daniel, R. and E. Maler, "XPointer xpointer() Scheme", World Wide Web Consortium WD WD-xptr-xpointer-20021219, December 2002. |
V02: 2013-11-22 MD
V01: 2013-09-26 MD
2013-06-02 MD Initial version