Internet DRAFT - draft-douglass-link-extension
draft-douglass-link-extension
Network Working Group M. Douglass
Internet-Draft RPI
Intended status: Standards Track May 9, 2011
Expires: November 10, 2011
Link Extension to Icalendar
draft-douglass-link-extension-01
Abstract
This specification introduces new iCalendar property LINK to provide
ancillary information for iCalendar components and changes RELATED-TO
to define temporal relationships.
Status of this Memo
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This Internet-Draft will expire on November 10, 2011.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions Used in This Document . . . . . . . . . . . . 3
2. Typed References . . . . . . . . . . . . . . . . . . . . . . . 3
3. Reference Types . . . . . . . . . . . . . . . . . . . . . . . 4
4. Link Relation Types . . . . . . . . . . . . . . . . . . . . . 4
5. Redefined Relation Type Value . . . . . . . . . . . . . . . . 4
6. New Property Parameters . . . . . . . . . . . . . . . . . . . 6
6.1. Rel . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.2. Gap . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.3. Title . . . . . . . . . . . . . . . . . . . . . . . . . . 7
7. New Parameter Values . . . . . . . . . . . . . . . . . . . . . 7
8. New Properties . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Link . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
9. Redefined RELATED-TO Property . . . . . . . . . . . . . . . . 9
9.1. RELATED-TO . . . . . . . . . . . . . . . . . . . . . . . . 9
10. Security Considerations . . . . . . . . . . . . . . . . . . . 11
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
13. Normative References . . . . . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
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]
In addition 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.
1.1. Conventions Used in This Document
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].
2. Typed References
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.
Project management tools often need to be able to specify the
relationships between the various events and tasks which make up a
project. This specification defines relation types for those
purposes.
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3. Reference Types
The actual reference value can take three forms specified by the type
parameter
URI: The default type. This is a URI referring to the target.
UID: This allows for linking within a single collection and the
value is assumed to be another component within that collection.
REFERENCE: An xpointer. In an XML environment it may be necessary
to refer to an external XML artifact. The XPointer is defined in
[W3C.WD-xptr-xpointer-20021219] and allows addressing portions of
XML documents.
4. Link Relation Types
[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].
5. Redefined Relation Type Value
Relationship parameter type values are defined in section 3.2.15. of
[RFC5545]. This specification redefines that type to include the new
values FINISHTOSTART, FINISHTOFINISH, STARTTOFINISH and STARTTOSTART.
Format Definition:
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This property parameter is defined by the following notation:
reltypeparam = "RELTYPE" "="
("PARENT" ; Parent relationship - Default
/ "CHILD" ; Child relationship
/ "SIBLING" ; Sibling relationship
/ "FINISHTOSTART"
/ "FINISHTOFINISH"
/ "STARTTOFINISH"
/ "STARTTOSTART"
/ iana-token ; Some other IANA-registered
; iCalendar relationship type
/ x-name) ; A non-standard, experimental
; relationship type
Description: This parameter can be specified on a property that
references another related calendar. The parameter may specify
the hierarchical relationship type of the calendar component
referenced by the property when the value is PARENT, CHILD or
SIBLING. It defines the temporal relationship when the value is
one of FINISHTOSTART, FINISHTOFINISH, STARTTOFINISH or
STARTTOSTART. If this parameter is not specified on an allowable
property, the default relationship type is PARENT. Applications
MUST treat x-name and iana-token values they don't recognize the
same way as they would the PARENT value.
RELTYPE=PARENT: Identifies the referenced calendar component is a
superior of calendar component
RELTYPE=CHILD: Indicates that the referenced calendar component is a
subordinate of the calendar component.
RELTYPE=SIBLING: Indicates that the referenced calendar component is
a peer of the calendar component.
RELTYPE=FINISHTOSTART: As soon as the Predecessor Interval finishes,
the Successor Interval starts. For example, when sanding is
complete, painting begins.
RELTYPE=FINISHTOFINISH: The Successor Interval continues as long as
the Predecessor Interval. For example, the concession stand stops
serving 20 minutes after the end of the game.
RELTYPE=STARTTOFINISH: The start of the Predecessor controls the
finish of the Successor. For example, the start of Attendee
Check-in controls the end of the interval "Set up registration
booth."
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RELTYPE=STARTTOSTART: The Predecessor Interval triggers the start of
the second task. The Gap indicates the lag time. For example, 20
minutes after the caterer begins work, the dining lines are open.
6. New Property Parameters
6.1. Rel
Parameter name: REL
Purpose: To specify the relationship of data referenced by a LINK
property.
Format Definition:
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
Description: This parameter MUST be specified on all LINK
properties, and defines the type of reference. This allows
programs consuming this data to automatically scan for references
they support. In addition to the values defined here any value
defined in [RFC5988] may be used. There is no default relation
type.
REL=SOURCE: identifies the source of the event information.
Registration: These relation types are registered in [RFC5988]
6.2. Gap
Parameter name: GAP
Purpose: To specify the length of the gap, positive or negative
between two temporally related components.
Format Definition:
This parameter is defined by the following notation:
gapparam = "GAP" "=" dur-value
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Description: This parameter MAY be specified on the RELATED-TO
property, and defines the duration of time between the predecessor
and successor in an interval.
6.3. Title
Parameter name: TITLE
Purpose: To provide a human readable title.
Format Definition:
This parameter is defined by the following notation:
titleparam = "TITLE" "=" text
Description: This parameter MAY be specified on all LINK properties,
and provides a human readable label, perhaps for icons or links..
7. New Parameter Values
This specification defines a new value to be used with the VALUE
property parameter:
UID VALUE=UID indicates that the associated value is the UID for a
component.
REFERENCE VALUE=REFERENCE indicates that the associated value is an
xpointer referencing an associated XML artifact.
8. New Properties
8.1. Link
Property name: LINK
Purpose: This property provides a reference to external information
about a component.
Value type: URI, TEXT or REFERENCE
Property Parameters: Non-standard, reference type or format type
parameters can be specified on this property.
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Conformance: This property MAY be specified in any iCalendar
component.
Description: When used in a component the value of this property
points to additional information related to the component. For
example, it may reference the originating web server.
Format Definition:
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
(";" gapparam) /
(";" fmttypeparam) /
(";" titleparam) /
; the following is OPTIONAL
; and MAY occur more than once
(";" xparam)
)
Example:
The following is an example of this property. It points to a
server acting as the source for the event.
LINK;REL=SOURCE;TITLE=The Egg:
http://example.com/events
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9. Redefined RELATED-TO Property
9.1. RELATED-TO
Property name: RELATED-TO
Purpose: This property is used to represent a relationship or
reference between one calendar component and another. The
definition here extends the definition in Section 3.8.4.5. of
[RFC5545] by allowing URI values adn a GAP parameter.
Value type: URI or TEXT
Property Parameters: Non-standard, reference type, gap, value or
format type parameters can be specified on this property.
Conformance: This property MAY be specified in any iCalendar
component.
Description: By default or when VALUE=UID is specified, the property
value consists of the persistent, globally unique identifier of
another calendar component. This value would be represented in a
calendar component by the "UID" property.
By default, the property value points to another calendar
component that has a PARENT relationship to the referencing
object. The "RELTYPE" property parameter is used to either
explicitly state the default PARENT relationship type to the
referenced calendar component or to override the default PARENT
relationship type and specify either a CHILD or SIBLING
relationship or a temporal relationship.
The PARENT relationship indicates that the calendar component is a
subordinate of the referenced calendar component. The CHILD
relationship indicates that the calendar component is a superior
of the referenced calendar component. The SIBLING relationship
indicates that the calendar component is a peer of the referenced
calendar component.
The FINISHTOSTART, FINISHTOFINISH, STARTTOFINISH or STARTTOSTART
relationships define temporal relationships as specified in the
reltype parameter definition.
Changes to a calendar component referenced by this property can
have an implicit impact on the related calendar component. For
example, if a group event changes its start or end date or time,
then the related, dependent events will need to have their start
and end dates changed in a corresponding way. Similarly, if a
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PARENT calendar component is cancelled or deleted, then there is
an implied impact to the related CHILD calendar components. This
property is intended only to provide information on the
relationship of calendar components. It is up to the target
calendar system to maintain any property implications of this
relationship.
Format Definition:
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)
;
)
Example:
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
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10. Security Considerations
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.
11. IANA Considerations
12. Acknowledgements
The author would like to thank Chuck Norris of eventful.com for his
work which led to the development of this RFC.
The author would also like to thank the members of the Calendaring
and Scheduling Consortium public events technical committee and the
following individuals for contributing their ideas and support:
Cyrus Daboo, Dan Mendell
The authors would also like to thank the Calendaring and Scheduling
Consortium for advice with this specification.
13. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[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.
[RFC5545] Desruisseaux, B., "Internet Calendaring and Scheduling
Core Object Specification (iCalendar)", RFC 5545,
September 2009.
[RFC5988] Nottingham, M., "Web Linking", RFC 5988, October 2010.
[W3C.REC-xml-20060816]
Yergeau, F., Paoli, J., Sperberg-McQueen, C., Maler, E.,
and T. Bray, "Extensible Markup Language (XML) 1.0 (Fourth
Edition)", World Wide Web Consortium FirstEdition REC-xml-
20060816, August 2006,
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<http://www.w3.org/TR/2006/REC-xml-20060816>.
[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,
<http://www.w3.org/TR/2002/WD-xptr-xpointer-20021219>.
Author's Address
Michael Douglass
Rensselaer Polytechnic Institute
110 8th Street
Troy, NY 12180
USA
Email: douglm@rpi.edu
URI: http://www.rpi.edu/
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