rfc9253.original   rfc9253.txt 
Network Working Group M. Douglass Internet Engineering Task Force (IETF) M. Douglass
Internet-Draft Bedework Request for Comments: 9253 Bedework
Updates: 5545 (if approved) 22 March 2022 Updates: 5545 July 2022
Intended status: Standards Track Category: Standards Track
Expires: 23 September 2022 ISSN: 2070-1721
Support for iCalendar Relationships Support for iCalendar Relationships
draft-ietf-calext-ical-relations-11
Abstract Abstract
This specification updates the iCalendar RELATED-TO property defined This specification updates the iCalendar RELATED-TO property defined
in RFC5545 by adding new relation types and introduces new iCalendar in RFC 5545 by adding new relation types and introduces new iCalendar
properties LINK, CONCEPT and REFID to allow better linking and properties (LINK, CONCEPT, and REFID) to allow better linking and
grouping of iCalendar components and related data. grouping of iCalendar components and related data.
Status of This Memo Status of This Memo
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction
1.1. Structured iCalendar relationships . . . . . . . . . . . 3 1.1. Structured iCalendar Relationships
1.2. Grouped iCalendar relationships . . . . . . . . . . . . . 3 1.2. Grouped iCalendar Relationships
1.3. Concept relationships . . . . . . . . . . . . . . . . . . 3 1.3. Concept Relationships
1.4. Linked relationships . . . . . . . . . . . . . . . . . . 4 1.4. Linked Relationships
1.5. Caching and offline use . . . . . . . . . . . . . . . . . 5 1.5. Caching and Offline Use
1.6. Conventions Used in This Document . . . . . . . . . . . . 5 1.6. Conventions Used in This Document
2. LINK Property Reference Types . . . . . . . . . . . . . . . . 5 2. LINK Property Reference Types
3. Link Relation Types . . . . . . . . . . . . . . . . . . . . . 6 3. Link Relation Types
4. New temporal RELTYPE Parameter values . . . . . . . . . . . . 6 4. New Temporal RELTYPE Parameter Values
5. Additional New RELTYPE Parameter Values . . . . . . . . . . . 8 5. Additional New RELTYPE Parameter Values
6. New Property Parameters . . . . . . . . . . . . . . . . . . . 8 6. New Property Parameters
6.1. Link Relation . . . . . . . . . . . . . . . . . . . . . . 9 6.1. Link Relation
6.2. Gap . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 6.2. Gap
7. New Value Data Types . . . . . . . . . . . . . . . . . . . . 10 7. New Value Data Types
8. New Properties . . . . . . . . . . . . . . . . . . . . . . . 11 8. New Properties
8.1. Concept . . . . . . . . . . . . . . . . . . . . . . . . . 11 8.1. Concept
8.2. Link . . . . . . . . . . . . . . . . . . . . . . . . . . 12 8.2. Link
8.3. Refid . . . . . . . . . . . . . . . . . . . . . . . . . . 14 8.3. Refid
9. Updates to RFC 5545 . . . . . . . . . . . . . . . . . . . . . 14 9. Updates to RFC 5545
9.1. RELATED-TO . . . . . . . . . . . . . . . . . . . . . . . 15 9.1. RELATED-TO
10. Security Considerations . . . . . . . . . . . . . . . . . . . 17 10. Security Considerations
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 11. IANA Considerations
11.1. iCalendar Property Registrations . . . . . . . . . . . . 17 11.1. iCalendar Property Registrations
11.2. iCalendar Property Parameter Registrations . . . . . . . 18 11.2. iCalendar Property Parameter Registrations
11.3. iCalendar Value Data Type Registrations . . . . . . . . 18 11.3. iCalendar Value Data Type Registrations
11.4. iCalendar RELTYPE Value Registrations . . . . . . . . . 19 11.4. iCalendar RELTYPE Value Registrations
11.5. New Reference Type Registration . . . . . . . . . . . . 19 12. References
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20 12.1. Normative References
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 20 12.2. Informative References
13.1. Informative References . . . . . . . . . . . . . . . . . 20 Acknowledgements
13.2. Normative References . . . . . . . . . . . . . . . . . . 20 Author's Address
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction 1. Introduction
iCalendar entities defined in [RFC5545] often need to be related to iCalendar entities defined in [RFC5545] often need to be related to
each other or to associated meta-data. The specifications below each other or to associated metadata. The specifications below
support relationships of the following forms: support relationships of the following forms:
Structured iCalendar: iCalendar entities can be related to each Structured iCalendar: iCalendar entities can be related to each
other in some structured way, for example as parent, sibling, other in some structured way, for example, as parent, sibling,
before, after. before, or after.
Grouped iCalendar: iCalendar entities can be related to each other Grouped iCalendar: iCalendar entities can be related to each other
as a group. CATEGORIES are often used for this purpose but are as a group. CATEGORIES are often used for this purpose but are
problematic for application developers due to their lack of problematic for application developers due to their lack of
consistency and use as a free-form tag. consistency and use as a free-form tag.
Linked: Entities can be linked to other entities such as vcards Linked: Entities can be linked to other entities, such as vCards,
through a URI and associated REL and FMTTYPE parameters. through a URI and associated REL and FMTTYPE parameters.
1.1. Structured iCalendar relationships 1.1. Structured iCalendar Relationships
The iCalendar [RFC5545] RELATED-TO property has no support for The iCalendar [RFC5545] RELATED-TO property has no support for
temporal relationships as used by project management tools. temporal relationships as used by project management tools.
The RELTYPE parameter is extended to take new values defining The RELTYPE parameter is extended to take new values defining
temporal relationships, a GAP parameter is defined to provide lead temporal relationships, a GAP parameter is defined to provide lead
and lag values, and RELATED-TO is extended to allow URI values. and lag values, and RELATED-TO is extended to allow URI values.
These changes allow the RELATED-TO property to define a richer set of These changes allow the RELATED-TO property to define a richer set of
relationships useful for project management. relationships useful for project management.
1.2. Grouped iCalendar relationships 1.2. Grouped iCalendar Relationships
This specification defines a new REFID property which allows This specification defines a new REFID property, which allows
arbitrary groups of entities to be associated with the same key arbitrary groups of entities to be associated with the same key
value. value.
REFID is used to identify a key allowing the association of REFID is used to identify a key allowing the association of
components that are all related to the referring, aggregating components that are all related to the referring, aggregating
component and the retrieval of components based on this key. For component and the retrieval of components based on this key. For
example, this may be used to identify the tasks associated with a example, this may be used to identify the tasks associated with a
given project without having to communicate the task structure of the given project without having to communicate the task structure of the
project. A further example is the grouping of all sub-tasks project. A further example is the grouping of all sub-tasks
associated with the delivery of a specific package in a package associated with the delivery of a specific package in a package
delivery system. delivery system.
As such, the presence of a REFID property imparts no meaning to the As such, the presence of a REFID property imparts no meaning to the
component. It is merely a key to allow retrieval. This is distinct component. It is merely a key to allow retrieval. This is distinct
from categorisation which, while allowing grouping also adds meaning from categorization, which, while allowing grouping, also adds
to the component to which it is attached. meaning to the component to which it is attached.
1.3. Concept relationships 1.3. Concept Relationships
The name CONCEPT is used by the Simple Knowledge Organization System The name CONCEPT is used by the Simple Knowledge Organization System,
defined in [W3C.REC-skos-reference-20090818]. The term "concept" as defined in [W3C.REC-skos-reference-20090818]. The term "concept"
more accurately defines what we often mean by a category. It's not more accurately defines what we often mean by a category. It's not
the text string that is important but the meaning attached to it. the text string that is important but the meaning attached to it.
For example, the term "football" can mean very different sports. For example, the term "football" can mean very different sports.
The introduction of CONCEPT allows a more structured approach to The introduction of CONCEPT allows a more structured approach to
categorization, with the possibility of namespaced and path-like categorization, with the possibility of namespaced and path-like
values. Unlike REFID the CONCEPT property imparts some meaning. It values. Unlike REFID, the CONCEPT property imparts some meaning. It
is assumed that the value of this property will reference a well is assumed that the value of this property will reference a well-
defined category. defined category.
The current [RFC5545] CATEGORY property is used as a free form The current CATEGORIES property defined in [RFC5545] is used as a
'tagging' field. These values have some meaning to those who apply free-form 'tagging' field. These values have some meaning to those
them but not necessarily to any consumer. As such it is difficult to who apply them but not necessarily to any consumer. As such, it is
establish formal relationships between components based on their difficult to establish formal relationships between components based
category. on their category.
Rather than attempt to add semantics to the CATEGORY property it Rather than attempt to add semantics to the CATEGORIES property, it
seems best to continue its usage as an informal tag and establish a seems best to continue its usage as an informal tag and establish a
new CONCEPT property with more constraints. new CONCEPT property with more constraints.
1.4. Linked relationships 1.4. Linked Relationships
The currently existing iCalendar standard [RFC5545] lacks a general The currently existing iCalendar standard [RFC5545] lacks a general
purpose method for referencing additional, external information purpose method for referencing additional, external information
relating to calendar components. relating to calendar components.
This document proposes a method for referencing typed external This document proposes a method for referencing typed external
information that can provide additional information about an information that can provide additional information about an
iCalendar component. This new LINK property is closely aligned to iCalendar component. This new LINK property is closely aligned to
[RFC8288] which defines the generic concept of Web Linking as well as [RFC8288], which defines the generic concept of Web Linking, as well
its expression in the HTTP LINK header field. as its expression in the HTTP LINK header field.
The LINK property defines a typed reference or relation to external The LINK property defines a typed reference or relation to external
meta-data or related resources. By providing type and format metadata or related resources. By providing type and format
information as parameters, clients and servers are able to discover information as parameters, clients and servers are able to discover
interesting references and make use of them, perhaps for indexing or interesting references and make use of them, perhaps for indexing or
the presentation of interesting links for the user. the presentation of interesting links for the user.
Calendar components are often grouped into collections to represent a Calendar components are often grouped into collections to represent a
calendar or a series of tasks, for example [RFC4791]' (CalDAV) calendar or a series of tasks, for example, Calendaring Extensions to
calendar collections. WebDAV (CalDAV) calendar collections [RFC4791].
It is also often necessary to reference calendar components in other It is also often necessary to reference calendar components in other
collections. For example, a VEVENT might refer to a VTODO from which collections. For example, a VEVENT might refer to a VTODO from which
it was derived. The PARENT, SIBLING and CHILD relationships defined it was derived. The PARENT, SIBLING, and CHILD relationships defined
for the RELATED-TO property only allow for a UID which is inadequate for the RELATED-TO property only allow for a unique identifier (UID),
for many purposes. Allowing other value types for those which is inadequate for many purposes. Allowing other value types
relationships may help but would cause backward compatibility issues. for those relationships may help but would cause backward-
The LINK property can link components in different collections or compatibility issues. The LINK property can link components in
even on different servers. different collections or even on different servers.
When publishing events it is useful to be able to refer back to the 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 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 from a feed or an ics file on a website. A LINK property can provide
provide a reference to the originator of the event. a reference to the originator of the event.
Beyond the need to relate elements temporally, project management Beyond the need to relate elements temporally, project management
tools often need to be able to specify the relationships between the tools often need to be able to specify the relationships between the
various events and tasks which make up a project. The LINK property various events and tasks that make up a project. The LINK property
provides such a mechanism. provides such a mechanism.
The LINK property MUST NOT be treated as just another attachment. The LINK property MUST NOT be treated as just another attachment.
The ATTACH property defined in [RFC5545] has been extended by The ATTACH property defined in [RFC5545] has been extended by
[RFC8607] to handle server-side management and stripping of inline [RFC8607] to handle server-side management and stripping of inline
data and to provide additional data about the attachment (size, data and to provide additional data about the attachment (size,
filename etc). filename, etc.).
Additionally clients may choose to handle attachments differently Additionally, clients may choose to handle attachments differently
from the LINK property as attachments are often an integral part of from the LINK property, as attachments are often an integral part of
the message - for example, the agenda. the message, for example, the agenda.
1.5. Caching and offline use 1.5. Caching and Offline Use
In general, the calendar entity should be self explanatory without In general, the calendar entity should be self explanatory without
the need to download referenced meta-data such as a web page. the need to download referenced metadata, such as a web page.
However, to facilitate offline display the link type may identify However, to facilitate offline display, the link type may identify
important pieces of data which should be downloaded in advance. important pieces of data that should be downloaded in advance.
1.6. Conventions Used in This Document 1.6. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY" and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in
14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
The notation used in this memo to (re-)define iCalendar elements is The notation used in this memo to (re-)define iCalendar elements is
the ABNF notation of [RFC5234] as used by [RFC5545]. Any syntax the ABNF notation of [RFC5234], as used by [RFC5545]. Any syntax
elements shown below that are not explicitly defined in this elements shown below that are not explicitly defined in this
specification come from iCalendar [RFC5545]. specification come from iCalendar [RFC5545].
2. LINK Property Reference Types 2. LINK Property Reference Types
The reference value in the LINK property defined below can take three The reference value in the LINK property defined below can take three
forms specified by the VALUE parameter: forms specified by the VALUE parameter:
URI: This is a URI referring to the target. URI: This is a URI referring to the target.
UID: This allows for linking within a single collection of calendar UID: This allows for linking within a single collection of calendar
components and the value MUST refer to another component within components, and the value MUST refer to another component within
the same collection. the same collection.
XML-REFERENCE: In an XML environment it may be necessary to refer to XML-REFERENCE: In an XML environment, it may be necessary to refer
a fragment of an external XML artifact. This value is a URI with to a fragment of an external XML artifact. This value is a URI
an XPointer anchor value. The XPointer is defined in with an XPointer anchor value. The XPointer is defined in
[W3C.WD-xptr-xpointer-20021219] and its use as an anchor is [W3C.WD-xptr-xpointer-20021219], and its use as an anchor is
defined in [W3C.REC-xptr-framework-20030325] defined in [W3C.REC-xptr-framework-20030325].
Note that UID references may need updating on import. An example, is Note that UID references may need updating on import. An example is
data to be imported from a file containing VTODO and VEVENT data to be imported from a file containing VTODO and VEVENT
components with a VTODO referring to VEVENT components by UID. When components, with a VTODO referring to VEVENT components by UID. When
imported into a CalDAV system, the VTODO components are typically imported into a CalDAV system, the VTODO components are typically
placed in a different collection from the VEVENT components. This placed in a different collection from the VEVENT components. This
would require the UID reference to be replaced with a URI. would require the UID reference to be replaced with a URI.
3. Link Relation Types 3. Link Relation Types
[RFC8288] defines two forms of relation type: registered and Two forms of relation types are defined in [RFC8288]: registered and
extension. Registered relation types are added to the Link Relations extension. Registered relation types are added to the "Link
registry as specified in Section 2.1.1 of [RFC8288]. Extension Relations" registry, as specified in Section 2.1.1 of [RFC8288].
relation types, defined in Section 2.1.2 of [RFC8288], are specified Extension relation types, defined in Section 2.1.2 of [RFC8288], are
as unique URIs that are not registered in the registry. specified as unique URIs that are not registered in the registry.
The relation types defined in Section 6.1 will be registered with The relation types defined in Section 6.1 will be registered with
IANA in accordance with the specifications in [RFC8288]. IANA in accordance with the specifications in [RFC8288].
4. New temporal RELTYPE Parameter values 4. New Temporal RELTYPE Parameter Values
This section defines the usual temporal relationships for use with This section defines the usual temporal relationships for use with
the RELTYPE parameter defined in Section 3.2.15 of [RFC5545]: the RELTYPE parameter defined in Section 3.2.15 of [RFC5545]:
FINISHTOSTART, FINISHTOFINISH, STARTTOFINISH or STARTTOSTART. FINISHTOSTART, FINISHTOFINISH, STARTTOFINISH, or STARTTOSTART.
The [RFC5545] RELATED-TO property with one or more of these temporal The [RFC5545] RELATED-TO property with one or more of these temporal
relationships will be present in the predecessor entity and will relationships will be present in the predecessor entity and will
refer to the successor entity. refer to the successor entity.
The GAP parameter (see Section 6.2) specifies the lead (a negative The GAP parameter (see Section 6.2) specifies the lead (a negative
value) or lag (a positive value) time between the predecessor and the value) or lag (a positive value) time between the predecessor and the
successor. successor.
In the description of each temporal relationship below we refer to In the description of each temporal relationship below, we refer to
Task-A, which contains and controls the relationship, and Task-B the Task-A, which contains and controls the relationship, and Task-B,
target of the relationship. This is indicated by the direction of which is the target of the relationship. This is indicated by the
the arrow in the diagrams below. direction of the arrows in the diagrams below.
Also each relationship may be modified by the addition of a GAP Also, each relationship may be modified by the addition of a GAP
parameter to the relationship which applies to the targeted parameter to the relationship that applies to the targeted component.
component.
RELTYPE=FINISHTOSTART: Task-B cannot start until Task-A finishes. RELTYPE=FINISHTOSTART: Task-B cannot start until Task-A finishes.
For example, when painting is complete, carpet-laying can begin. For example, when painting is complete, carpet laying can begin.
============ ============
| Task-A | | Task-A |
============ ============
| |
V V
============ ============
| Task-B | | Task-B |
============ ============
Figure 1: Finish to start relationship Figure 1: Finish-to-Start Relationship
RELTYPE=FINISHTOFINISH: Task-B can only be completed after Task-A is RELTYPE=FINISHTOFINISH: Task-B can only be completed after Task-A is
finished. The related tasks may run in parallel before finished. The related tasks may run in parallel before
completion. completion.
For example, in the development of two related pieces of software, For example, in the development of two related pieces of software
e.g. the api and the implementation, the design of the (e.g., the API and the implementation), the design of the
implementation (B) cannot be completed until the design of the api implementation (Task-B) cannot be completed until the design of
(A) has been completed. the API (Task-A) has been completed.
================== ==================
| Task-A |--+ | Task-A |--+
================== | ================== |
| |
============ | ============ |
| Task-B |<-+ | Task-B |<-+
============ ============
Figure 2: Finish to finish relationship Figure 2: Finish-to-Finish Relationship
RELTYPE=STARTTOFINISH: The start of Task-A (which occurs after Task- RELTYPE=STARTTOFINISH: The start of Task-A (which occurs after Task-
B) controls the finish of Task-B. For example, ticket sales B) controls the finish of Task-B. For example, ticket sales
(Task-B) end after the game starts (Task-A). (Task-B) end after the game starts (Task-A).
============ ============
+--| Task-A | +--| Task-A |
| ============ | ============
+---------+ +---------+
============ | ============ |
| Task-B |<-+ | Task-B |<-+
============ ============
Figure 3: Start to finish relationship Figure 3: Start-to-Finish Relationship
RELTYPE=STARTTOSTART: The start of Task-A triggers the start of 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-B, that is, Task-B can start anytime after Task-A starts.
============ ============
+--| Task-A | +--| Task-A |
| ============ | ============
| |
| ============ | ============
+->| Task-B | +->| Task-B |
============ ============
Figure 4: Start to start relationship Figure 4: Start-to-Start Relationship
5. Additional New RELTYPE Parameter Values 5. Additional New RELTYPE Parameter Values
This section defines the additional relationships below: This section defines the additional relationships below:
RELTYPE=FIRST: Indicates that the referenced calendar component is RELTYPE=FIRST: This indicates that the referenced calendar component
the first in a series the referencing calendar component is part is the first in a series the referencing calendar component is
of. part of.
RELTYPE=NEXT: Indicates that the referenced calendar component is RELTYPE=NEXT: This indicates that the referenced calendar component
the next in a series the referencing calendar component is part is the next in a series the referencing calendar component is part
of. of.
RELTYPE=DEPENDS-ON: Indicates that the current calendar component RELTYPE=DEPENDS-ON: This indicates that the current calendar
depends on the referenced calendar component in some manner. For component depends on the referenced calendar component in some
example a task may be blocked waiting on the other, referenced, manner. For example, a task may be blocked waiting on the other,
task. referenced, task.
RELTYPE=REFID: Establishes a reference from the current component to RELTYPE=REFID: This establishes a reference from the current
components with a REFID property which matches the value given in component to components with a REFID property that matches the
the associated RELATED-TO property. value given in the associated RELATED-TO property.
RELTYPE=CONCEPT: Establishes a reference from the current component RELTYPE=CONCEPT: This establishes a reference from the current
to components with a CONCEPT property which matches the value component to components with a CONCEPT property that matches the
given in the associated RELATED-TO property. value given in the associated RELATED-TO property.
Note that the relationship types of PARENT, CHILD and SIBLING Note that the relationship types of PARENT, CHILD, and SIBLING
establish a hierarchical relationship. The new types of FIRST and establish a hierarchical relationship. The new types of FIRST and
NEXT are an ordering relationship. NEXT are an ordering relationship.
6. New Property Parameters 6. New Property Parameters
6.1. Link Relation 6.1. Link Relation
Parameter name: LINKREL Parameter name: LINKREL
Purpose: To specify the relationship of data referenced by a LINK Purpose: This property specifies the relationship of data referenced
property. by a LINK property.
Format Definition: This parameter is defined by the following Format Definition: This parameter is defined by the following
notation: notation:
linkrelparam = "LINKREL" "=" linkrelparam = "LINKREL" "="
("SOURCE" ; Link to source of this component (DQUOTE uri DQUOTE
/ DQUOTE uri DQUOTE / iana-token) ; Other IANA registered 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. There is no default relation type.
In addition to the value defined here any link relation in the Description: This parameter MUST be specified on all LINK properties
link registry established by [RFC8288], or new link relations, may and define the type of reference. This allows programs consuming
be used. this data to automatically scan for references they support.
There is no default relation type.
It is expected that link relation types seeing significant usage Any link relation in the link registry established by [RFC8288],
in calendaring will have the calendaring usage described in an or new link relations, may be used. It is expected that link
RFC. relation types seeing significant usage in calendaring will have
the calendaring usage described in an RFC.
LINKREL=SOURCE: identifies the source of the event information. LINKREL=latest-version: This identifies the latest version of the
event information.
Registration: These relation types are registered in [RFC8288] Registration: These relation types are registered in [RFC8288].
6.2. Gap 6.2. Gap
Parameter name: GAP Parameter name: GAP
Purpose: To specify the length of the gap, positive or negative, Purpose: This property specifies the length of the gap, positive or
between two components with a temporal relationship. negative, between two components with a temporal relationship.
Format Definition: This parameter is defined by the following Format Definition: This parameter is defined by the following
notation where dur-value is defined in section 3.3.6 of [RFC5545]. notation, where dur-value is defined in Section 3.3.6 of
: [RFC5545]. :
gapparam = "GAP" "=" dur-value gapparam = "GAP" "=" dur-value
Description: This parameter MAY be specified on the RELATED-TO Description: This parameter MAY be specified on the RELATED-TO
property, and defines the duration of time between the predecessor property and defines the duration of time between the predecessor
and successor in an interval. When positive it defines the lag and successor in an interval. When positive, it defines the lag
time between a task and its logical successor. When negative it time between a task and its logical successor. When negative, it
defines the lead time. defines the lead time.
An example of lag time might be if task A is "paint the room" and An example of lag time might be if Task-A is "paint the room" and
task B is "lay the carpets" then task A may be related to task B Task-B is "lay the carpets". Then, Task-A may be related to
with RELTYPE=FINISHTOSTART with a gap of 1 day - long enough for Task-B with RELTYPE=FINISHTOSTART with a gap of 1 day -- long
the paint to dry. enough for the paint to dry.
==================== ====================
| Paint the room |--+ | paint the room |--+
==================== | ==================== |
|(lag of one day) |(lag of one day)
| |
| =============== | ===================
+->| lay carpet | +->| lay the carpet |
=============== ===================
Figure 5: Finish to start relationship with lag Figure 5: Finish-to-Start Relationship with Lag
For an example of lead time, in constructing a two storey building For an example of lead time, in constructing a two-story building,
the electrical work must be done before painting. However the the electrical work must be done before painting. However, the
painter can move in to the first floor as the electricians move painter can move in to the first floor as the electricians move
upstairs. upstairs.
===================== =====================
| Electrical work |--+ | electrical work |--+
===================== | ===================== |
+-------------+ +-------------+
|(lead of estimated time) |(lead of estimated time)
| ================== | ==================
+->| Painting | +->| painting |
================== ==================
Figure 6: Finish to start relationship with lead Figure 6: Finish-to-Start Relationship with Lead
7. New Value Data Types 7. New Value Data Types
This specification defines the following new value types to be used This specification defines the following new value types to be used
with the VALUE property parameter: with the VALUE property parameter:
UID VALUE=UID indicates that the associated value is the UID for a UID: VALUE=UID indicates that the associated value is the UID for a
component. component.
XML-REFERENCE VALUE=XML-REFERENCE indicates that the associated XML-REFERENCE: VALUE=XML-REFERENCE indicates that the associated
value references an associated XML artifact and is a URI with an value references an associated XML artifact and is a URI with an
XPointer anchor value. The XPointer is defined in XPointer anchor value. The XPointer is defined in
[W3C.WD-xptr-xpointer-20021219] and its use as an anchor is [W3C.WD-xptr-xpointer-20021219], and its use as an anchor is
defined in [W3C.REC-xptr-framework-20030325]. defined in [W3C.REC-xptr-framework-20030325].
8. New Properties 8. New Properties
8.1. Concept 8.1. Concept
Property name: CONCEPT Property name: CONCEPT
Purpose: This property defines the formal categories for a calendar Purpose: This property defines the formal categories for a calendar
component. component.
Value type: URI Value type: URI
Property Parameters: IANA, and non-standard parameters can be Property Parameters: IANA and non-standard parameters can be
specified on this property. specified on this property.
Conformance: This property can be specified zero or more times in Conformance: This property can be specified zero or more times in
any iCalendar component. any iCalendar component.
Description: This property is used to specify formal categories or Description: This property is used to specify formal categories or
classifications of the calendar component. The values are useful classifications of the calendar component. The values are useful
in searching for a calendar component of a particular type and in searching for a calendar component of a particular type and
category. category.
This categorization is distinct from the more informal "tagging" This categorization is distinct from the more informal "tagging"
of components provided by the existing CATEGORIES property. It is of components provided by the existing CATEGORIES property. It is
expected that the value of the CONCEPT property will reference an expected that the value of the CONCEPT property will reference an
external resource which provides information about the external resource that provides information about the
categorization. categorization.
In addition, a structured URI value allows for hierarchical In addition, a structured URI value allows for hierarchical
categorization of events. categorization of events.
Possible category resources are the various proprietary systems, Possible category resources are the various proprietary systems,
for example Library of Congress, or an open source of for example, the Library of Congress, or an open source of
categorisation data. categorization data.
Format Definition: This property is defined by the following Format Definition: This property is defined by the following
notation: notation:
concept = "CONCEPT" conceptparam ":" concept = "CONCEPT" conceptparam ":"
uri CRLF uri CRLF
conceptparam = *(";" other-param) conceptparam = *(";" other-param)
Example: The following is an example of this property. It points to Example: The following is an example of this property. It points to
skipping to change at page 12, line 17 skipping to change at line 523
CONCEPT:https://example.com/event-types/arts/music CONCEPT:https://example.com/event-types/arts/music
8.2. Link 8.2. Link
Property name: LINK Property name: LINK
Purpose: This property provides a reference to external information Purpose: This property provides a reference to external information
related to a component. related to a component.
Value type: URI, UID or XML-REFERENCE Value type: URI, UID, or XML-REFERENCE
Property Parameters: The VALUE parameter is required. Non-standard, Property Parameters: The VALUE parameter is required. Non-standard,
link relation type, format type, label and language parameters can link relation type, format type, label, and language parameters
also be specified on this property. The LABEL parameter is can also be specified on this property. The LABEL parameter is
defined in [RFC7986]. defined in [RFC7986].
Conformance: This property can be specified zero or more times in Conformance: This property can be specified zero or more times in
any iCalendar component. any iCalendar component.
Description: When used in a component the value of this property Description: When used in a component, the value of this property
points to additional information related to the component. For points to additional information related to the component. For
example, it may reference the originating web server. example, it may reference the originating web server.
Format Definition: This property is defined by the following Format Definition: This property is defined by the following
notation: notation:
link = "LINK" linkparam ":" link = "LINK" linkparam ":"
( uri / ; for VALUE=XML-REFERENCE ( uri / ; for VALUE=XML-REFERENCE
uri / ; for VALUE=URI uri / ; for VALUE=URI
text ) ; for VALUE=UID text ) ; for VALUE=UID
CRLF CRLF
linkparam = ; the elements herein may appear in any order, linkparam = (";" "VALUE" "=" ("XML-REFERENCE" /
; and the order is not significant. "URI" /
"UID"))
(";" "VALUE" "=" ("XML-REFERENCE" /
"URI" /
"UID"))
1*(";" linkrelparam) 1*(";" linkrelparam)
1*(";" fmttypeparam) 1*(";" fmttypeparam)
1*(";" labelparam) 1*(";" labelparam)
1*(";" languageparam) 1*(";" languageparam)
*(";" other-param) *(";" other-param)
; the elements herein may appear in any order,
; and the order is not significant.
This property is a serialisation of the model in [RFC8288], where This property is a serialization of the model in [RFC8288], where
the link target is carried in the property value, the link context the link target is carried in the property value, the link context
is the containing calendar entity, and the link relation type and is the containing calendar entity, and the link relation type and
any target attributes are carried in iCalendar property any target attributes are carried in iCalendar property
parameters. parameters.
The LINK property parameters map to [RFC8288] attributes as The LINK property parameters map to [RFC8288] attributes as
follows: follows:
LABEL: Maps to the "title" attribute defined in section 3.4.1 of LABEL: This parameter maps to the "title" attribute defined in
[RFC8288]. Section 3.4.1 of [RFC8288].
LANGUAGE: Maps to the "hreflang" attribute defined in section LANGUAGE: This parameter maps to the "hreflang" attribute defined
3.4.1 of [RFC8288]. in Section 3.4.1 of [RFC8288].
LINKREL: Maps to the link relation type defined in section 2.1 of LINKREL: This parameter maps to the link relation type defined in
[RFC8288]. Section 2.1 of [RFC8288].
FMTTYPE: Maps to the "type" attribute defined in section 3.4.1 of FMTTYPE: This parameter maps to the "type" attribute defined in
[RFC8288]. Section 3.4.1 of [RFC8288].
There is no mapping for [RFC8288] "title*", "anchor", "rev" or There is no mapping for "title*", "anchor", "rev", or "media"
"media". [RFC8288].
Example: The following is an example of this property which provides Example: The following is an example of this property, which
a reference to the source for the calendar object. provides a reference to the source for the calendar object.
LINK;LINKREL=SOURCE;LABEL=Venue;VALUE=URI: LINK;LINKREL=SOURCE;LABEL=Venue;VALUE=URI:
https://example.com/events https://example.com/events
Example: The following is an example of this property which provides Example: The following is an example of this property, which
a reference to an entity from which this one was derived. The provides a reference to an entity from which this one was derived.
link relation is a vendor defined value. The link relation is a vendor-defined value.
LINK;LINKREL="https://example.com/linkrel/derivedFrom"; LINK;LINKREL="https://example.com/linkrel/derivedFrom";
VALUE=URI: VALUE=URI:
https://example.com/tasks/01234567-abcd1234.ics https://example.com/tasks/01234567-abcd1234.ics
Example: The following is an example of this property which provides Example: The following is an example of this property, which
a reference to a fragment of an XML document. The link relation provides a reference to a fragment of an XML document. The link
is a vendor defined value. relation is a vendor-defined value.
LINK;LINKREL="https://example.com/linkrel/costStructure"; LINK;LINKREL="https://example.com/linkrel/costStructure";
VALUE=XML-REFERENCE: VALUE=XML-REFERENCE:
https://example.com/xmlDocs/bidFramework.xml https://example.com/xmlDocs/bidFramework.xml
#xpointer(descendant::CostStruc/range-to( #xpointer(descendant::CostStruc/range-to(
following::CostStrucEND[1])) following::CostStrucEND[1]))
8.3. Refid 8.3. Refid
Property name: REFID Property name: REFID
skipping to change at page 14, line 34 skipping to change at line 634
the events in a travel itinerary would have the same REFID value, the events in a travel itinerary would have the same REFID value,
so as to be grouped together. so as to be grouped together.
Format Definition: This property is defined by the following Format Definition: This property is defined by the following
notation: notation:
refid = "REFID" refidparam ":" text CRLF refid = "REFID" refidparam ":" text CRLF
refidparam = *(";" other-param) refidparam = *(";" other-param)
The current link registry
Example: The following is an example of this property. Example: The following is an example of this property.
REFID:itinerary-2014-11-17 REFID:itinerary-2014-11-17
9. Updates to RFC 5545 9. Updates to RFC 5545
This specification updates the RELATED-TO property defined in This specification updates the RELATED-TO property defined in
Section 3.8.4.5 of [RFC5545]. The contents of Section 9.1 replace Section 3.8.4.5 of [RFC5545]. The contents of Section 9.1 replace
that section. that section.
The RELTYPE parameter is extended to take new values defining The RELTYPE parameter is extended to take new values defining
temporal relationships, a GAP parameter is defined to provide lead temporal relationships, a GAP parameter is defined to provide lead
and lag values, and RELATED-TO is extended to allow URI values. and lag values, and RELATED-TO is extended to allow URI values.
These changes allow the RELATED-TO property to define a richer set of These changes allow the RELATED-TO property to define a richer set of
relationships useful for project management. relationships useful for project management.
9.1. RELATED-TO 9.1. RELATED-TO
Property Name: RELATED-TO Property name: RELATED-TO
Purpose: This property is used to represent a relationship or Purpose: This property is used to represent a relationship or
reference between one calendar component and another. The reference between one calendar component and another. The
definition here extends the definition in Section 3.8.4.5 of definition here extends the definition in Section 3.8.4.5 of
[RFC5545] by allowing URI or UID values and a GAP parameter. [RFC5545] by allowing URI or UID values and a GAP parameter.
Value Type: URI, UID or TEXT Value Type: URI, UID, or TEXT
Property Parameters: Relationship type, IANA and non-standard Property Parameters: Relationship type, IANA, and non-standard
property parameters can be specified on this property. property parameters can be specified on this property.
Conformance: This property MAY be specified in any iCalendar Conformance: This property MAY be specified in any iCalendar
component. component.
Description: By default or when VALUE=UID is specified, the property Description: By default or when VALUE=UID is specified, the property
value consists of the persistent, globally unique identifier of value consists of the persistent, globally unique identifier of
another calendar component. This value would be represented in a another calendar component. This value would be represented in a
calendar component by the "UID" property. calendar component by the UID property.
By default, the property value points to another calendar By default, the property value points to another calendar
component that has a PARENT relationship to the referencing component that has a PARENT relationship to the referencing
object. The "RELTYPE" property parameter is used to either object. The RELTYPE property parameter is used to either
explicitly state the default PARENT relationship type to the explicitly state the default PARENT relationship type to the
referenced calendar component or to override the default PARENT referenced calendar component or to override the default PARENT
relationship type and specify either a CHILD or SIBLING relationship type and specify either a CHILD or SIBLING
relationship or a temporal relationship. relationship or a temporal relationship.
The PARENT relationship indicates that the calendar component is a The PARENT relationship indicates that the calendar component is a
subordinate of the referenced calendar component. The CHILD subordinate of the referenced calendar component. The CHILD
relationship indicates that the calendar component is a superior relationship indicates that the calendar component is a superior
of the referenced calendar component. The SIBLING relationship of the referenced calendar component. The SIBLING relationship
indicates that the calendar component is a peer of the referenced indicates that the calendar component is a peer of the referenced
calendar component. calendar component.
To preserve backwards compatibility the value type MUST be UID To preserve backwards compatibility, the value type MUST be UID
when the PARENT, SIBLING or CHILD relationships are specified. when the PARENT, SIBLING, or CHILD relationships are specified.
The FINISHTOSTART, FINISHTOFINISH, STARTTOFINISH or STARTTOSTART The FINISHTOSTART, FINISHTOFINISH, STARTTOFINISH, or STARTTOSTART
relationships define temporal relationships as specified in the relationships define temporal relationships, as specified in the
reltype parameter definition. RELTYPE parameter definition.
The FIRST and NEXT define ordering relationships between calendar The FIRST and NEXT define ordering relationships between calendar
components. components.
The DEPENDS-ON relationship indicates that the current calendar The DEPENDS-ON relationship indicates that the current calendar
component depends on the referenced calendar component in some component depends on the referenced calendar component in some
manner. For example a task may be blocked waiting on the other, manner. For example, a task may be blocked waiting on the other,
referenced, task. referenced, task.
The REFID and CONCEPT relationships establish a reference from the The REFID and CONCEPT relationships establish a reference from the
current component to the referenced component. current component to the referenced component.
Changes to a calendar component referenced by this property can Changes to a calendar component referenced by this property can
have an implicit impact on the related calendar component. For have an implicit impact on the related calendar component. For
example, if a group event changes its start or end date or time, example, if a group event changes its start or end date or time,
then the related, dependent events will need to have their start then the related, dependent events will need to have their start
and end dates changed in a corresponding way. Similarly, if a and end dates and times changed in a corresponding way.
PARENT calendar component is cancelled or deleted, then there is Similarly, if a PARENT calendar component is canceled or deleted,
an implied impact to the related CHILD calendar components. This then there is an implied impact to the related CHILD calendar
property is intended only to provide information on the components. This property is intended only to provide information
relationship of calendar components. on the relationship of calendar components.
Deletion of the target component, for example the target of a Deletion of the target component, for example, the target of a
FIRST, NEXT or temporal relationship can result in broken links. FIRST, NEXT, or temporal relationship, can result in broken links.
It is up to the target calendar system to maintain any property It is up to the target calendar system to maintain any property
implications of these relationships. implications of these relationships.
Format Definition: This property is defined by the following Format Definition: This property is defined by the following
notation: notation:
related = "RELATED-TO" relparam ":" related = "RELATED-TO" relparam ":"
( text / ; for VALUE=UID ( text / ; for VALUE=UID
uri / ; for VALUE=URI uri / ; for VALUE=URI
skipping to change at page 17, line 15 skipping to change at line 751
RELATED-TO:jsmith.part7.19960817T083000.xyzMail@example.com RELATED-TO:jsmith.part7.19960817T083000.xyzMail@example.com
RELATED-TO:19960401-080045-4000F192713-0052@example.com RELATED-TO:19960401-080045-4000F192713-0052@example.com
RELATED-TO;VALUE=URI;RELTYPE=STARTTOFINISH: RELATED-TO;VALUE=URI;RELTYPE=STARTTOFINISH:
https://example.com/caldav/user/jb/cal/ https://example.com/caldav/user/jb/cal/
19960401-080045-4000F192713.ics 19960401-080045-4000F192713.ics
10. Security Considerations 10. Security Considerations
All of the security considerations of section 7 pf [RFC5545] apply to All of the security considerations of Section 7 of [RFC5545] apply to
this specification. this specification.
Applications using the LINK property need to be aware of the risks Applications using the LINK property need to be aware of the risks
entailed in using the URIs provided as values. See section 7 of entailed in using the URIs provided as values. See Section 7 of
[RFC3986] for a discussion of the security considerations relating to [RFC3986] for a discussion of the security considerations relating to
URIs. URIs.
In particular note section 7.1 "Reliability and Consistency" of In particular, note Section 7.1 (Reliability and Consistency) of
[RFC3986] which points out the lack of a stability guarantee for [RFC3986], which points out the lack of a stability guarantee for
referenced resources. referenced resources.
When the value is an XML-REFERENCE type the targeted data is an XML When the value is an XML-REFERENCE type, the targeted data is an XML
document or portion thereof. Consumers need to be aware of the document or portion thereof. Consumers need to be aware of the
security issues related to XML processing - in particular those security issues related to XML processing -- in particular, those
related to XML entities. See [RFC4918] - Section 20.6. Additionally related to XML entities. See Section 20.6 of [RFC4918].
note that the reference may be invalid or become so over time. Additionally, note that the reference may be invalid or become so
over time.
The CONCEPT and redefined RELATED-TO property have the same issues in The CONCEPT and redefined RELATED-TO properties have the same issues
that values may be URIs. in that values may be URIs.
Extremely large values for the GAP parameter may lead to unexpected Extremely large values for the GAP parameter may lead to unexpected
behavior. behavior.
11. IANA Considerations 11. IANA Considerations
11.1. iCalendar Property Registrations 11.1. iCalendar Property Registrations
The following iCalendar property names have been added to the The following iCalendar property names have been added to the
iCalendar Properties Registry defined in Section 8.3.2 of [RFC5545]. iCalendar "Properties" registry defined in Section 8.3.2 of
IANA has also added a reference to this document where the properties [RFC5545]. IANA has also added a reference to this document, where
originally defined in [RFC5545] have been updated by this document. the properties originally defined in [RFC5545] have been updated by
this document.
+============+=========+========================+ +============+=========+=============================+
| Property | Status | Reference | | Property | Status | Reference |
+============+=========+========================+ +============+=========+=============================+
| CONCEPT | Current | Section 8.1 | | CONCEPT | Current | Section 8.1 |
+------------+---------+------------------------+ +------------+---------+-----------------------------+
| LINK | Current | Section 8.2 | | LINK | Current | Section 8.2 |
+------------+---------+------------------------+ +------------+---------+-----------------------------+
| REFID | Current | Section 8.3 | | REFID | Current | Section 8.3 |
+------------+---------+------------------------+ +------------+---------+-----------------------------+
| RELATED-TO | Current | [RFC5545], Section 9.1 | | RELATED-TO | Current | [RFC5545], Section 3.8.4.5; |
+------------+---------+------------------------+ | | | RFC 9253, Section 9.1 |
+------------+---------+-----------------------------+
Table 1 Table 1
11.2. iCalendar Property Parameter Registrations 11.2. iCalendar Property Parameter Registrations
The following iCalendar property parameter names have been added to The following iCalendar property parameter names have been added to
the iCalendar Parameters Registry defined in Section 8.3.3 of the iCalendar "Parameters" registry defined in Section 8.3.3 of
[RFC5545]. [RFC5545].
+===========+=========+=============+ +===========+=========+=============+
| Parameter | Status | Reference | | Parameter | Status | Reference |
+===========+=========+=============+ +===========+=========+=============+
| GAP | Current | Section 6.2 | | GAP | Current | Section 6.2 |
+-----------+---------+-------------+ +-----------+---------+-------------+
| LINKREL | Current | Section 6.1 | | LINKREL | Current | Section 6.1 |
+-----------+---------+-------------+ +-----------+---------+-------------+
Table 2 Table 2
11.3. iCalendar Value Data Type Registrations 11.3. iCalendar Value Data Type Registrations
The following iCalendar property parameter names have been added to The following iCalendar property parameter names have been added to
the iCalendar Value Data Types Registry defined in Section 8.3.4 of the iCalendar "Value Data Types" registry defined in Section 8.3.4 of
[RFC5545]. [RFC5545].
+=================+=========+===========+ +=================+=========+===========+
| Value Data Type | Status | Reference | | Value Data Type | Status | Reference |
+=================+=========+===========+ +=================+=========+===========+
| XML-REFERENCE | Current | Section 7 | | XML-REFERENCE | Current | Section 7 |
+-----------------+---------+-----------+ +-----------------+---------+-----------+
| UID | Current | Section 7 | | UID | Current | Section 7 |
+-----------------+---------+-----------+ +-----------------+---------+-----------+
Table 3 Table 3
11.4. iCalendar RELTYPE Value Registrations 11.4. iCalendar RELTYPE Value Registrations
The following iCalendar "RELTYPE" values have been added to the The following iCalendar "RELTYPE" values have been added to the
iCalendar Relationship Types Registry defined in Section 8.3.8 of iCalendar "Relationship Types" registry defined in Section 8.3.8 of
[RFC5545]. [RFC5545].
+===================+=========+===========+ +===================+=========+===========+
| Relationship Type | Status | Reference | | Relationship Type | Status | Reference |
+===================+=========+===========+ +===================+=========+===========+
| CONCEPT | Current | Section 5 | | CONCEPT | Current | Section 5 |
+-------------------+---------+-----------+ +-------------------+---------+-----------+
| DEPENDS-ON | Current | Section 5 | | DEPENDS-ON | Current | Section 5 |
+-------------------+---------+-----------+ +-------------------+---------+-----------+
| FINISHTOFINISH | Current | Section 4 | | FINISHTOFINISH | Current | Section 4 |
skipping to change at page 19, line 35 skipping to change at line 863
+-------------------+---------+-----------+ +-------------------+---------+-----------+
| REFID | Current | Section 5 | | REFID | Current | Section 5 |
+-------------------+---------+-----------+ +-------------------+---------+-----------+
| STARTTOFINISH | Current | Section 4 | | STARTTOFINISH | Current | Section 4 |
+-------------------+---------+-----------+ +-------------------+---------+-----------+
| STARTTOSTART | Current | Section 4 | | STARTTOSTART | Current | Section 4 |
+-------------------+---------+-----------+ +-------------------+---------+-----------+
Table 4 Table 4
11.5. New Reference Type Registration 12. References
The following link relation values have been added to the Reference
Types Registry defined in Section 6.2.2 of [RFC8288].
+========+=========+=============+
| Name | Status | Reference |
+========+=========+=============+
| SOURCE | Current | Section 6.1 |
+--------+---------+-------------+
Table 5
12. Acknowledgements
The author would like to thank the members of CalConnect, the
Calendaring and Scheduling Consortium technical committees and the
following individuals for contributing their ideas, support and
comments:
Adrian Apthorp, Cyrus Daboo, Marten Gajda, Ken Murchison
The author would also like to thank CalConnect, the Calendaring and
Scheduling Consortium for advice with this specification.
13. References
13.1. Informative References
[RFC4791] Daboo, C., Desruisseaux, B., and L. Dusseault,
"Calendaring Extensions to WebDAV (CalDAV)", RFC 4791,
DOI 10.17487/RFC4791, March 2007,
<https://www.rfc-editor.org/info/rfc4791>.
[RFC8607] Daboo, C., Quillaud, A., and K. Murchison, Ed.,
"Calendaring Extensions to WebDAV (CalDAV): Managed
Attachments", RFC 8607, DOI 10.17487/RFC8607, June 2019,
<https://www.rfc-editor.org/info/rfc8607>.
13.2. Normative References 12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005, RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>. <https://www.rfc-editor.org/info/rfc3986>.
skipping to change at page 21, line 24 skipping to change at line 906
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8288] Nottingham, M., "Web Linking", RFC 8288, [RFC8288] Nottingham, M., "Web Linking", RFC 8288,
DOI 10.17487/RFC8288, October 2017, DOI 10.17487/RFC8288, October 2017,
<https://www.rfc-editor.org/info/rfc8288>. <https://www.rfc-editor.org/info/rfc8288>.
[W3C.REC-skos-reference-20090818] [W3C.REC-skos-reference-20090818]
Miles, A. and S. Bechhofer, "SKOS Simple Knowledge Miles, A. and S. Bechhofer, "SKOS Simple Knowledge
Organization System Reference", World Wide Web Consortium Organization System Reference", W3C Recommendation REC-
Recommendation REC-skos-reference-20090818, 18 August skos-reference-20090818, 18 August 2009,
2009,
<https://www.w3.org/TR/2009/REC-skos-reference-20090818>. <https://www.w3.org/TR/2009/REC-skos-reference-20090818>.
[W3C.REC-xptr-framework-20030325] [W3C.REC-xptr-framework-20030325]
Grosso, P., Maler, E., Marsh, J., and N. Walsh, "XPointer Grosso, P., Maler, E., Marsh, J., and N. Walsh, "XPointer
Framework", World Wide Web Consortium Recommendation REC- Framework", W3C Recommendation REC-xptr-framework-
xptr-framework-20030325, 25 March 2003, 20030325, 25 March 2003,
<https://www.w3.org/TR/2003/REC-xptr-framework-20030325>. <https://www.w3.org/TR/2003/REC-xptr-framework-20030325>.
[W3C.WD-xptr-xpointer-20021219] [W3C.WD-xptr-xpointer-20021219]
DeRose, S., Daniel, R., and E. Maler, "XPointer xpointer() DeRose, S., Maler, E., and R. Daniel, "XPointer xpointer()
Scheme", World Wide Web Consortium WD WD-xptr-xpointer- Scheme", W3C WD WD-xptr-xpointer-20021219, 19 December
20021219, 19 December 2002, 2002,
<http://www.w3.org/TR/2002/WD-xptr-xpointer-20021219>. <http://www.w3.org/TR/2002/WD-xptr-xpointer-20021219>.
12.2. Informative References
[RFC4791] Daboo, C., Desruisseaux, B., and L. Dusseault,
"Calendaring Extensions to WebDAV (CalDAV)", RFC 4791,
DOI 10.17487/RFC4791, March 2007,
<https://www.rfc-editor.org/info/rfc4791>.
[RFC8607] Daboo, C., Quillaud, A., and K. Murchison, Ed.,
"Calendaring Extensions to WebDAV (CalDAV): Managed
Attachments", RFC 8607, DOI 10.17487/RFC8607, June 2019,
<https://www.rfc-editor.org/info/rfc8607>.
Acknowledgements
The author would like to thank the members of CalConnect, the
Calendaring and Scheduling Consortium technical committees, and the
following individuals for contributing their ideas, support, and
comments:
Adrian Apthorp, Cyrus Daboo, Marten Gajda, and Ken Murchison
The author would also like to thank CalConnect and the Calendaring
and Scheduling Consortium for advice with this specification.
Author's Address Author's Address
Michael Douglass Michael Douglass
Bedework Bedework
226 3rd Street 226 3rd Street
Troy, NY 12180 Troy, NY 12180
United States of America United States of America
Email: mdouglass@bedework.com Email: mdouglass@bedework.com
URI: https://bedework.com URI: https://bedework.com
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