Internet DRAFT - draft-douglass-ical-relations
draft-douglass-ical-relations
Network Working Group M. Douglass
Internet-Draft RPI
Intended status: Standards Track January 14, 2015
Expires: July 18, 2015
Support for Icalendar Relationships
draft-douglass-ical-relations-04
Abstract
This specification updates RELATED-TO and introduces new iCalendar
properties LINK, STRUCTURED-CATEGORY and REFID 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 July 18, 2015.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Structured iCalendar relationships . . . . . . . . . . . 3
1.2. Grouped iCalendar relationships . . . . . . . . . . . . . 3
1.3. Structured category relationships . . . . . . . . . . . . 3
1.4. Linked relationships . . . . . . . . . . . . . . . . . . 3
1.5. Caching and offline use . . . . . . . . . . . . . . . . . 4
1.6. Conventions Used in This Document . . . . . . . . . . . . 4
2. Reference Types . . . . . . . . . . . . . . . . . . . . . . . 4
3. Link Relation Types . . . . . . . . . . . . . . . . . . . . . 5
4. Redefined Relation Type Value . . . . . . . . . . . . . . . . 5
5. New Property Parameters . . . . . . . . . . . . . . . . . . . 8
5.1. Rel . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.2. Gap . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6. New Value Data Types . . . . . . . . . . . . . . . . . . . . 9
7. New Properties . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Structured-Category . . . . . . . . . . . . . . . . . . . 9
7.2. Link . . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.3. Refid . . . . . . . . . . . . . . . . . . . . . . . . . . 12
8. Redefined RELATED-TO Property . . . . . . . . . . . . . . . . 12
8.1. RELATED-TO . . . . . . . . . . . . . . . . . . . . . . . 13
9. Security Considerations . . . . . . . . . . . . . . . . . . . 15
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
10.1. iCalendar Property Registrations . . . . . . . . . . . . 15
10.2. iCalendar Property Parameter Registrations . . . . . . . 15
10.3. iCalendar Value Data Type Registrations . . . . . . . . 15
10.4. iCalendar RELTYPE Value Registrations . . . . . . . . . 16
10.5. New Reference Type Registration . . . . . . . . . . . . 16
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16
12. Normative References . . . . . . . . . . . . . . . . . . . . 17
Appendix A. Change log . . . . . . . . . . . . . . . . . . . . . 17
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 18
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.
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Linked: Entities are linked to each other through typed references.
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 REFID property which allows
arbitrary groups of entities to be associated with the same key
value. The presence of a REFID property imparts no meaning to the
event. It is merely a key to allow retrieval.
1.3. Structured category relationships
The introduction of STRUCTURED-CATEGORY allows a more structured
approach to categorization, with the possibility of namespaced and
path-like values. Unlike REFID the category imparts some meaning.
It is assumed that the value of this property will reference a well
defined category.
1.4. 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
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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.
The LINK property SHOULD NOT be treated as just another attachment.
The ATTACH property is being extended to handle server-side
management and stripping of inline data. Clients may choose to
handle attachments differently as they are often an integral part of
the message - for example, the agenda.
1.5. Caching and offline use
To facilitate offline display the link type may identify important
pieces of data which should be downloaded in advance.
In general, the calendar entity should be self explanatory without
the need to download referenced meta-data such as a web page.
1.6. 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
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[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:
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
/ "REFID" ; Relationship based on REFID
/ "STRUCTURED-CATEGORY"
; Relationship based on STRUCTURED-CATEGORY
/ "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
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
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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: See [RFC5545] section 3.2.15.
RELTYPE=CHILD: See [RFC5545] section 3.2.15.
RELTYPE=SIBLING: See [RFC5545] section 3.2.15.
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=REFID: Establishes a reference from the current component to
components with a REFID property which matches the value given in
the associated RELATED-TO property.
RELTYPE=STRUCTURED-CATEGORY: Establishes a reference from the
current component to components with a STRUCTURED-CATEGORY
property which matches the value given in the associated RELATED-
TO property.
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
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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
(Task-B) end when the game starts (Task-A).
============
+--| Task-A |
| ============
|
============ |
| Task-B |<-+
============
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
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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]
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. When positive it defines the lag
time between a task and its logical successor. When negative it
defines the lead time.
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An example of lag time might be if task A is "paint the room" and
task B is "hang the drapes" then task A may be related to task B
with RELTYPE=FINISHTOSTART with a gap long enough for the paint to
dry.
An example of lead time might be to relate a 1 week task A to the
end of task B with RELTYPE=STARTTOFINISH and a negative gap of 1
week so they finish at the same time.
6. New Value Data Types
This specification defines the following new value types 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
7.1. Structured-Category
Property name: STRUCTURED-CATEGORY
Purpose: This property defines the formal categories for a calendar
component.
Value type: URI
Property Parameters: IANA, and non-standard parameters can be
specified on this property.
Conformance: This property can be specified zero or more times in
any iCalendar component.
Description: This property is used to specify formal categories or
classifications of the calendar component. The values are useful
in searching for a calendar component of a particular type and
category.
Within the "VEVENT", "VTODO", or "VJOURNAL" calendar components,
more than one formal category can be specified by using multiple
properties.
This categorization is distinct from the more informal "tagging"
of components provided by the existing CATEGORIES property. It is
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expected that the value of the STRUCTURED-CATEGORY property will
reference an external resource which provides information about
the categorization.
In addition, a structured URI value allows for hierarchical
categorization of events.
Format Definition:
This property is defined by the following notation:
structured-category = "STRUCTURED-CATEGORY" structcatparam ":" uri CRLF
structcatparam = *(
;
; The following is OPTIONAL,
; and MAY occur more than once.
;
(";" other-param)
;
)
Example:
The following is an example of this property. It points to a server
acting as the source for the calendar object.
STRUCTURED-CATEGORY:http://example.com/event-types/sports
STRUCTURED-CATEGORY:http://example.com/event-types/arts/music
STRUCTURED-CATEGORY:http://example.com/task-types/delivery
7.2. 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.
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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
(";" fmttypeparam) /
(";" labelparam) /
; labelparam is defined in ...
; 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 calendar object.
LINK;REL=SOURCE;LABEL=The Egg:http://example.com/events
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7.3. Refid
Property name: REFID
Purpose: This property value acts as a key for associated iCalendar
entities.
Value type: TEXT
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 text identifier that
allows associated components to be located or retrieved as a
whole. For example all of the events in a travel itinerary would
have the same REFID value.
Format Definition:
This property is defined by the following notation:
refid = "REFID" refidparam ":" text CRLF
refidparam = *(
; the following is OPTIONAL
; and MAY occur more than once
(";" xparam)
)
Example:
The following is an example of this property.
REFID:itinerary-2014-11-17
8. Redefined RELATED-TO Property
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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 and 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
PARENT calendar component is cancelled or deleted, then there is
an implied impact to the related CHILD calendar components. This
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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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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.
The STRUCTURED-CATEGORY and redefined RELATED-TO property have the
same issues in that values may be URIs.
10. IANA Considerations
10.1. iCalendar Property Registrations
The following iCalendar property names have been added to the
iCalendar Properties Registry defined in Section 8.3.2 of [RFC5545]
+---------------------+---------+-------------+
| Property | Status | Reference |
+---------------------+---------+-------------+
| LINK | Current | Section 7.2 |
| REFID | Current | Section 7.3 |
| STRUCTURED-CATEGORY | Current | Section 7.1 |
+---------------------+---------+-------------+
10.2. iCalendar Property Parameter Registrations
The following iCalendar property parameter names have been added to
the iCalendar Parameters Registry defined in Section 8.3.3 of
[RFC5545]
+---------------------+---------+-------------+
| Parameter | Status | Reference |
+---------------------+---------+-------------+
| REL | Current | Section 5.1 |
| GAP | Current | Section 5.2 |
| STRUCTURED-CATEGORY | Current | Section 7.1 |
+---------------------+---------+-------------+
10.3. iCalendar Value Data Type Registrations
The following iCalendar property parameter names have been added to
the iCalendar Value Data Types Registry defined in Section 8.3.4 of
[RFC5545]
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+-----------------+---------+-----------+
| Value Data Type | Status | Reference |
+-----------------+---------+-----------+
| UID | Current | Section 6 |
| REFERENCE | Current | Section 6 |
+-----------------+---------+-----------+
10.4. iCalendar RELTYPE Value Registrations
The following iCalendar "RELTYPE" values have been added to the
iCalendar Relationship Types Registry defined in Section 8.3.8 of
[RFC5545]
+---------------------+---------+-----------+
| Parameter | Status | Reference |
+---------------------+---------+-----------+
| REL | Current | Section 4 |
| DEPENDS-ON | Current | Section 4 |
| REFID | Current | Section 4 |
| STRUCTURED-CATEGORY | Current | Section 4 |
| FINISHTOSTART | Current | Section 4 |
| FINISHTOFINISH | Current | Section 4 |
| STARTTOFINISH | Current | Section 4 |
| STARTTOSTART | Current | Section 4 |
+---------------------+---------+-----------+
10.5. New Reference Type Registration
The following link relation values have been added to the Reference
Types Registry defined in Section 6.2.2 of [RFC5988]
+--------+---------+-------------+
| Name | Status | Reference |
+--------+---------+-------------+
| SOURCE | Current | Section 5.1 |
+--------+---------+-------------+
11. Acknowledgements
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.
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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.
[W3C.REC-xml-20060816]
Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E., and
F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fourth
Edition)", World Wide Web Consortium Recommendation 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>.
Appendix A. Change log
V04: 2014-11-18 MD
o Add 5545 registrations.
o Drop Q-name in favor of URI.
o Change REFID value type to text.
o Add STRUCTURED-CATEGORY property.
o Add STRUCTURED-CATEGORY relationship to RELATED-TO.
V03: 2014-09-21 MD
o Added Q-name specification.
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o Change RELATED-ID to REFID and change its value type to Q-name.
o Add REFID relationship to RELATED-TO.
V02: 2013-11-22 MD
o Added more description to GAP
V01: 2013-09-26 MD
o Removed "Improved" from title
o Fixed typos and examples
o Removed gap param from link
2013-06-02 MD Initial version
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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