Improved Support for Icalendar Relationships
draft-douglass-ical-relations-00
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
|
|
|---|---|---|---|
| Author | Mike Douglass | ||
| Last updated | 2013-07-02 | ||
| Replaced by | draft-ietf-calext-ical-relations, draft-ietf-calext-ical-relations, RFC 9253 | ||
| RFC stream | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
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draft-douglass-ical-relations-00
Network Working Group M. Douglass
Internet-Draft RPI
Intended status: Standards Track July 02, 2013
Expires: January 03, 2014
Improved Support for Icalendar Relationships
draft-douglass-ical-relations-00
Abstract
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.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on January 03, 2014.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Structured iCalendar relationships . . . . . . . . . . . 3
1.2. Grouped iCalendar relationships . . . . . . . . . . . . . 3
1.3. Linked relationships . . . . . . . . . . . . . . . . . . 3
1.4. Conventions Used in This Document . . . . . . . . . . . . 4
2. Reference Types . . . . . . . . . . . . . . . . . . . . . . . 4
3. Link Relation Types . . . . . . . . . . . . . . . . . . . . . 4
4. Redefined Relation Type Value . . . . . . . . . . . . . . . . 4
5. New Property Parameters . . . . . . . . . . . . . . . . . . . 7
5.1. Rel . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.2. Gap . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.3. Title . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6. New Parameter Values . . . . . . . . . . . . . . . . . . . . 8
7. New Properties . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Link . . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.2. Related-id . . . . . . . . . . . . . . . . . . . . . . . 10
8. Redefined RELATED-TO Property . . . . . . . . . . . . . . . . 12
8.1. RELATED-TO . . . . . . . . . . . . . . . . . . . . . . . 12
9. Security Considerations . . . . . . . . . . . . . . . . . . . 14
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14
12. Normative References . . . . . . . . . . . . . . . . . . . . 14
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction
Icalendar entities often need to be related to each other or to
associated meta-data. These relationships can take the following
forms
Structured iCalendar: Icalendar entities are related to each other
in some structured way, for example as parent, sibling, before,
after.
Grouped iCalendar: Icalendar entities are related to each other as a
group. CATEGORIES are often used for this purpose but are
problematic for application developers.
Linked: Icalendar entities and non-iCalendar entities are linked to
each other.
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1.1. Structured iCalendar relationships
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.
1.2. Grouped iCalendar relationships
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.
1.3. Linked relationships
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.
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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.
1.4. 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. 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.
3. 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].
4. 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
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.
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
/ "DEPENDS-ON"
/ "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 component. The parameter may
specify the hierarchical relationship type of the calendar
component referenced by the property when the value is PARENT,
CHILD or SIBLING. 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.
It defines the temporal relationship when the value is one of the
project management standard relationships FINISHTOSTART,
FINISHTOFINISH, STARTTOFINISH or STARTTOSTART. This property will
be present in the predecessor entity and will refer to the
successor entity. The GAP parameter specifies the lead or lag
time between the predecessor and the successor. In the
description of each temporal relationship below we refer to Task-A
which contains and controls the relationship and Task-B the target
of the relationship.
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.
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RELTYPE=DEPENDS-ON: Indicates that the current calendar component
depends on the referenced calendar component in some manner. For
example a task may be blocked waiting on the other, referenced,
task.
RELTYPE=FINISHTOSTART: Task-B cannot start until Task-A finishes.
For example, when sanding is complete, painting can begin.
============
| Task-A |--+
============ |
|
V
============
| Task-B |
============
Figure 1: Finish to start relationship
RELTYPE=FINISHTOFINISH: Task-B cannot finish before Task-A is
finished, that is the end of Task-A defines the end of Task-B.
For example, we start the potatoes, then the meat then the peas
but they should all be cooked at the same time.
============
| Task-A |--+
============ |
|
============ |
| Task-B |<-+
============
Figure 2: Finish to finish relationship
RELTYPE=STARTTOFINISH: The start of Task-A (which occurs after
Task-B) controls the finish of Task-B. For example, ticket sales
end when the game starts.
============
+--| Task-A |
| ============
|
============ |
| Task-B |<-+
============
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Figure 3: Start to finish relationship
RELTYPE=STARTTOSTART: The start of Task-A triggers the start of
Task-B, that is Task-B can start anytime after Task-A starts.
============
+--| Task-A |
| ============
|
| ============
+->| Task-B |
============
Figure 4: Start to start relationship
5. New Property Parameters
5.1. 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]
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5.2. 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
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.
5.3. 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..
6. 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.
7. New Properties
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7.1. 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.
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:
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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
7.2. Related-id
Property name: RELATED-ID
Purpose: This property allows iCalendar entities to be grouped.
Value type: TEXT
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Property Parameters: Non-standard parameters can be specified on
this property.
Conformance: This property MAY be specified multiple times in any
iCalendar component.
Description: The value of this property is a namespaced value using
Clark notation, that is the namespace is enclosd in braces, "{",
"}". The part following the namespace is defined by the owner of
that namespace and may be simple text, a path or any appropriate
text value.
In effect this property provides a more controlled categorization
of calendar entities.
A CUA MUST preserve any RELATED-ID property with a namespace it
does not recognize or own. This allows other CUAs to use the
RELATED-ID to define groups which only have significance to that
application. For example, a project management tol may flag all
tasks that form part of a specific project, or an itinerary tool
may flag all events that are part of an itinerary.
Format Definition:
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)
)
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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8. Redefined RELATED-TO Property
8.1. 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.
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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
9. 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.
10. IANA Considerations
11. 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.
12. 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.
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[W3C.REC-xml-20060816]
Sperberg-McQueen, C., Paoli, J., Maler, E., Yergeau, F.,
and T. Bray, "Extensible Markup Language (XML) 1.0 (Fourth
Edition)", World Wide Web Consortium FirstEdition REC-
xml-20060816, August 2006,
<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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