< draft-ietf-calext-ical-relations-08.txt		draft-ietf-calext-ical-relations-09.txt >
	Network Working Group M. Douglass		Network Working Group M. Douglass
	Internet-Draft Bedework		Internet-Draft Bedework
	Updates: 5545 (if approved) October 13, 2021		Updates: 5545 (if approved) 23 January 2022
	Intended status: Standards Track		Intended status: Standards Track
	Expires: April 16, 2022		Expires: 27 July 2022
	Support for iCalendar Relationships		Support for iCalendar Relationships
	draft-ietf-calext-ical-relations-08		draft-ietf-calext-ical-relations-09
	Abstract		Abstract
	This specification updates RELATED-TO defined in iCalendar (RFC5545)		This specification updates the iCalendar RELATED-TO property by
	and introduces new iCalendar properties LINK, CONCEPT and REFID to		adding new relation types and introduces new iCalendar properties
	allow better linking and grouping of iCalendar components and related		LINK, CONCEPT and REFID to allow better linking and grouping of
	data.		iCalendar components and related data.
	Status of This Memo		Status of This Memo
	This Internet-Draft is submitted in full conformance with the		This Internet-Draft is submitted in full conformance with the
	provisions of BCP 78 and BCP 79.		provisions of BCP 78 and BCP 79.
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at https://datatracker.ietf.org/drafts/current/.		Drafts is at https://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on April 16, 2022.		This Internet-Draft will expire on 27 July 2022.
	Copyright Notice		Copyright Notice
	Copyright (c) 2021 IETF Trust and the persons identified as the		Copyright (c) 2022 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
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	described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	1.1. Structured iCalendar relationships . . . . . . . . . . . 3		1.1. Structured iCalendar relationships . . . . . . . . . . . 3
	1.2. Grouped iCalendar relationships . . . . . . . . . . . . . 3		1.2. Grouped iCalendar relationships . . . . . . . . . . . . . 3
	1.3. Concept relationships . . . . . . . . . . . . . . . . . . 3		1.3. Concept relationships . . . . . . . . . . . . . . . . . . 3
	1.4. Linked relationships . . . . . . . . . . . . . . . . . . 4		1.4. Linked relationships . . . . . . . . . . . . . . . . . . 4
	1.5. Caching and offline use . . . . . . . . . . . . . . . . . 5		1.5. Caching and offline use . . . . . . . . . . . . . . . . . 5
	1.6. Conventions Used in This Document . . . . . . . . . . . . 5		1.6. Conventions Used in This Document . . . . . . . . . . . . 5
	2. Reference Types . . . . . . . . . . . . . . . . . . . . . . . 5		2. Reference Types . . . . . . . . . . . . . . . . . . . . . . . 5
	3. Link Relation Types . . . . . . . . . . . . . . . . . . . . . 5		3. Link Relation Types . . . . . . . . . . . . . . . . . . . . . 6
	4. New temporal RELTYPE Parameter values . . . . . . . . . . . . 6		4. New temporal RELTYPE Parameter values . . . . . . . . . . . . 6
	5. Additional New RELTYPE Parameter Values . . . . . . . . . . . 7		5. Additional New RELTYPE Parameter Values . . . . . . . . . . . 7
	6. New Property Parameters . . . . . . . . . . . . . . . . . . . 8		6. New Property Parameters . . . . . . . . . . . . . . . . . . . 8
	6.1. Link Relation . . . . . . . . . . . . . . . . . . . . . . 8		6.1. Link Relation . . . . . . . . . . . . . . . . . . . . . . 8
	6.2. Gap . . . . . . . . . . . . . . . . . . . . . . . . . . . 8		6.2. Gap . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
	7. New Value Data Types . . . . . . . . . . . . . . . . . . . . 9		7. New Value Data Types . . . . . . . . . . . . . . . . . . . . 9
	8. New Properties . . . . . . . . . . . . . . . . . . . . . . . 9		8. New Properties . . . . . . . . . . . . . . . . . . . . . . . 9
	8.1. Concept . . . . . . . . . . . . . . . . . . . . . . . . . 9		8.1. Concept . . . . . . . . . . . . . . . . . . . . . . . . . 9
	8.2. Link . . . . . . . . . . . . . . . . . . . . . . . . . . 10		8.2. Link . . . . . . . . . . . . . . . . . . . . . . . . . . 10
	8.3. Refid . . . . . . . . . . . . . . . . . . . . . . . . . . 12		8.3. Refid . . . . . . . . . . . . . . . . . . . . . . . . . . 12
	9. Redefined RELATED-TO Property . . . . . . . . . . . . . . . . 12		9. Updates to RFC 5545 . . . . . . . . . . . . . . . . . . . . . 13
	9.1. RELATED-TO . . . . . . . . . . . . . . . . . . . . . . . 12		9.1. RELATED-TO . . . . . . . . . . . . . . . . . . . . . . . 13
	10. Security Considerations . . . . . . . . . . . . . . . . . . . 14		10. Security Considerations . . . . . . . . . . . . . . . . . . . 15
	11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14		11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
	11.1. iCalendar Property Registrations . . . . . . . . . . . . 14		11.1. iCalendar Property Registrations . . . . . . . . . . . . 16
	11.2. iCalendar Property Parameter Registrations . . . . . . . 15		11.2. iCalendar Property Parameter Registrations . . . . . . . 16
	11.3. iCalendar Value Data Type Registrations . . . . . . . . 15		11.3. iCalendar Value Data Type Registrations . . . . . . . . 16
	11.4. iCalendar RELTYPE Value Registrations . . . . . . . . . 15		11.4. iCalendar RELTYPE Value Registrations . . . . . . . . . 17
	11.5. New Reference Type Registration . . . . . . . . . . . . 16		11.5. New Reference Type Registration . . . . . . . . . . . . 17
	12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16		12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 18
	13. References . . . . . . . . . . . . . . . . . . . . . . . . . 16		13. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
	13.1. Informative References . . . . . . . . . . . . . . . . . 16		13.1. Informative References . . . . . . . . . . . . . . . . . 18
	13.2. Normative References . . . . . . . . . . . . . . . . . . 17		13.2. Normative References . . . . . . . . . . . . . . . . . . 18
	Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 17		Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 19
	1. Introduction		1. Introduction
	iCalendar entities often need to be related to each other or to		iCalendar entities defined in [RFC5545] often need to be related to
	associated meta-data. The specifications below support relationships		each other or to associated meta-data. The specifications below
	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, 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 currently existing iCalendar [RFC5545] RELATED-TO property has no		The iCalendar [RFC5545] RELATED-TO property has no support for
	support for temporal relationships as used by standard project		temporal relationships as used by standard project management tools.
	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
	skipping to change at page 5, line 40 ¶		skipping to change at page 5, line 45 ¶
	2. Reference Types		2. Reference Types
	The actual reference value can take three forms specified by the type		The actual reference value can take three forms specified by the type
	parameter		parameter
	URI: The default type. This is a URI referring to the target.		URI: The default type. This is a URI referring to the target.
	UID: This allows for linking within a single collection and the		UID: This allows for linking within a single collection and the
	value MUST be another component within that collection.		value MUST be another component within that collection.
	REFERENCE: An XPointer. In an XML environment it may be necessary		REFERENCE: In an XML environment it may be necessary to refer to a
	to refer to an external XML artifact. The XPointer is defined in		fragment of an external XML artifact. This value is a URI with an
	[W3C.WD-xptr-xpointer-20021219] and allows addressing portions of		XPointer anchor value. The XPointer is defined in
	XML documents.		[W3C.WD-xptr-xpointer-20021219] and it's use as an anchor is
			defined in [W3C.REC-xptr-framework-20030325]
	3. Link Relation Types		3. Link Relation Types
	[RFC8288] defines two forms of relation type: registered and		[RFC8288] defines two forms of relation type: registered and
	extension. Registered relation types are added to the Link Relations		extension. Registered relation types are added to the Link Relations
	registry as specified in Section 2.1.1 of [RFC8288]. Extension		registry as specified in Section 2.1.1 of [RFC8288]. Extension
	relation types, defined in Section 2.1.2 of [RFC8288], are specified		relation types, defined in Section 2.1.2 of [RFC8288], are specified
	as unique URIs that are not registered in the registry.		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
	skipping to change at page 6, line 27 ¶		skipping to change at page 6, line 35 ¶
	The GAP parameter (see Section 6.2) specifies the lead or lag time		The GAP parameter (see Section 6.2) specifies the lead or lag time
	between the predecessor and the successor. In the description of		between the predecessor and the successor. In the description of
	each temporal relationship below we refer to Task-A, which contains		each temporal relationship below we refer to Task-A, which contains
	and controls the relationship, and Task-B the target of the		and controls the relationship, and Task-B the target of the
	relationship.		relationship.
	RELTYPE=FINISHTOSTART: Task-B cannot start until Task-A finishes.		RELTYPE=FINISHTOSTART: Task-B cannot start until Task-A finishes.
	For example, when sanding is complete, painting can begin.		For example, when sanding is complete, painting 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, if the goal is to prepare a meal, we start the		For example, if the goal is to prepare a meal, we start the
	potatoes, then the meat then the peas but they should all be		potatoes, then the meat then the peas but they should all be
	cooked at the same time.		cooked at the same time.
	==================		==================
	| 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 when the game starts (Task-A).		(Task-B) end when 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: Indicates that the referenced calendar component is
	the first in a series the referenced calendar component is part		the first in a series the referenced calendar component is part
	of.		of.
	RELTYPE=DEPENDS-ON: Indicates that the current calendar component		RELTYPE=DEPENDS-ON: Indicates that the current calendar component
	skipping to change at page 8, line 27 ¶		skipping to change at page 8, line 25 ¶
	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: To specify the relationship of data referenced by a LINK
	property.		property.
	Format Definition:		Format Definition: This parameter is defined by the following
			notation:
	This parameter is defined by the following notation:
	linkrelparam = "REL" "="		linkrelparam = "LINKREL" "="
	("SOURCE" ; Link to source of this component		("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		Description: This parameter MUST be specified on all LINK
	properties, and defines the type of reference. This allows		properties, and defines the type of reference. This allows
	programs consuming this data to automatically scan for references		programs consuming this data to automatically scan for references
	they support. In addition to the values defined here any value		they support. There is no default relation type.
	defined in [RFC8288] may be used. There is no default relation
	type.
	REL=SOURCE: identifies the source of the event information.		In addition to the values defined here any value defined in
			[RFC8288] may be used. However these uses SHOULD be documented in
			an RFC updating both [RFC5545] and [RFC8288]
			LINKREL=SOURCE: identifies the source 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: To specify the length of the gap, positive or negative,
	between two temporaly related components.		between two temporaly related components.
	Format Definition:		Format Definition: This parameter is defined by the following
			notation:
	This parameter is defined by the following notation:
	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 "hang the drapes" then task A may be related to task B		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		with RELTYPE=FINISHTOSTART with a gap long enough for the paint to
	skipping to change at page 9, line 34 ¶		skipping to change at page 9, line 33 ¶
	week so they finish at the same time.		week so they finish at the same time.
	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.
	REFERENCE VALUE=REFERENCE indicates that the associated value is an		REFERENCE VALUE=REFERENCE indicates that the associated value
	XPointer referencing an associated XML artifact.		references an associated XML artifact and is a URI with an
			XPointer anchor value. The XPointer is defined in
			[W3C.WD-xptr-xpointer-20021219] and it's use as an anchor is
			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.
	skipping to change at page 10, line 27 ¶		skipping to change at page 10, line 30 ¶
	external resource which provides information about the		external resource which 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 Library of Congress, or an open source of
	categorisation data.		categorisation data.
	Format Definition:		Format Definition: This property is defined by the following
			notation:
	This property is defined by the following notation:
	concept = "CONCEPT" conceptparam ":"
	uri CRLF
	conceptparam = *(";" other-param)		concept = "CONCEPT" conceptparam ":"
			uri CRLF
	Example:		conceptparam = *(";" other-param)
	The following is an example of this property. It points to a server		Example: The following is an example of this property. It points to
	acting as the source for the calendar object.		a server acting as the source for the calendar object.
	CONCEPT:http://example.com/event-types/arts/music		CONCEPT:http://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
	about a component.		related to a component.
	Value type: URI, TEXT or REFERENCE		Value type: URI, TEXT or REFERENCE
	Property Parameters: The VALUE parameter is required. Non-standard,		Property Parameters: The VALUE parameter is required. Non-standard,
	reference type or format type parameters can also be specified on		reference type or format type parameters can also be specified on
	this property. The LABEL parameter is defined in [RFC7986]		this property. The LABEL parameter is 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:		Format Definition: This property is defined by the following
			notation:
	This property is defined by the following notation:		link = "LINK" linkparam ":"
			( uri / ; for VALUE=REFERENCE
			uri / ; for VALUE=URI
			text ) ; for VALUE=TEXT
			CRLF
	link = "LINK" linkparam ":"		linkparam = ; the elements herein may appear in any order,
	( text / ; for VALUE=REFERENCE		; and the order is not significant.
	uri / ; for VALUE=URI
	text ) ; for VALUE=TEXT
	CRLF
	linkparam = ; the elements herein may appear in any order,		(";" "VALUE" "=" ("REFERENCE" /
	; and the order is not significant.		"URI" /
			"TEXT"))
			1*(";" linkrelparam)
			(";" fmttypeparam)
			(";" labelparam)
			(";" langparam)
			*(";" other-param)
	(";" "VALUE" "=" ("UID" /		This property is a serialisation of the model in [RFC8288], where
	"URI" /		the link target is carried in the property value, the link context
	"TEXT"))		is the containing calendar entity, and the link relation type and
	1*(";" linkrelparam)		any target attributes are carried in iCalendar property
	(";" fmttypeparam)		parameters.
	(";" labelparam)
	*(";" other-param)
	Example:		The LINK property parameters map to [RFC8288] attributes as
			follows:
	The following is an example of this property which provides a		LABEL: Maps to the "title" attribute defined in section 3.4.1 of
	reference to the source for the calendar object.		[RFC8288].
	LINK;LINKREL=SOURCE;LABEL=Venue;VALUE=URI:http://example.com/events		LANG: Maps to the "hreflang" attribute defined in section 3.4.1
			of [RFC8288].
	Example:		LINKREL: Maps to the link relation type defined in section 2.1 of
			[RFC8288].
	The following is an example of this property which provides a		FMTTYPE: Maps to the "type" attribute defined in section 3.4.1 of
	reference to an entity from which this one was derived. The link		[RFC8288].
	relation is a vendor defined value
	LINK;LINKREL="https://example.com/linkrel/derivedFrom";VALUE=URI:		There is no mapping for [RFC8288] "title*", "anchor", "rev" or
	http://example.com/tasks/01234567-abcd1234.ics		"media".
			Example: The following is an example of this property which provides
			a reference to the source for the calendar object.
			LINK;LINKREL=SOURCE;LABEL=Venue;VALUE=URI:http://example.com/events
			Example: The following is an example of this property which provides
			a reference to an entity from which this one was derived. The
			link relation is a vendor defined value
			LINK;LINKREL="https://example.com/linkrel/derivedFrom";VALUE=URI:
			http://example.com/tasks/01234567-abcd1234.ics
			Example: The following is an example of this property which provides
			a reference to a fragment of an XML document. The link relation
			is a vendor defined value
			LINK;LINKREL="https://example.com/linkrel/costStructure";
			VALUE=REFERENCE:
			http://example.com/xmlDocs/bidFramework.xml
			#xpointer(descendant::CostStruc/range-to(following::CostStrucEND[1]))
	8.3. Refid		8.3. Refid
	Property name: REFID		Property name: REFID
	Purpose: This property value acts as a key for associated iCalendar		Purpose: This property value acts as a key for associated iCalendar
	entities.		entities.
	Value type: TEXT		Value type: TEXT
	skipping to change at page 12, line 27 ¶		skipping to change at page 13, line 10 ¶
	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: The value of this property is free-form text that		Description: The value of this property is free-form text that
	creates an identifier for associated components. All components		creates an identifier for associated components. All components
	that use the same REFID value are associated through that value		that use the same REFID value are associated through that value
	and can be located or retrieved as a group. For example, all of		and can be located or retrieved as a group. For example, all of
	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:		Format Definition: This property is defined by the following
			notation:
	This property is defined by the following notation:		refid = "REFID" refidparam ":" text CRLF
	refid = "REFID" refidparam ":" text CRLF		refidparam = *(";" other-param)
	refidparam = *(";" other-param)		The current link registry
	Example:		Example: The following is an example of this property.
	The following is an example of this property.		REFID:itinerary-2014-11-17
	REFID:itinerary-2014-11-17		9. Updates to RFC 5545
	9. Redefined RELATED-TO Property		This specification updates the RELATED-TO property defined in
			Section 3.8.4.5 of [RFC5545].
			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 allow the RELATED-TO property to define a richer set of
			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.
	skipping to change at page 13, line 52 ¶		skipping to change at page 14, line 44 ¶
	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 changed in a corresponding way. Similarly, if a
	PARENT calendar component is cancelled or deleted, then there is		PARENT calendar component is cancelled or deleted, then there is
	an implied impact to the related CHILD calendar components. This		an implied impact to the related CHILD calendar components. This
	property is intended only to provide information on the		property is intended only to provide information on the
	relationship of calendar components. It is up to the target		relationship of calendar components. It is up to the target
	calendar system to maintain any property implications of this		calendar system to maintain any property implications of this
	relationship.		relationship.
	Format Definition:		Format Definition: This property is defined by the following
			notation:
	This property is defined by the following notation:
	related = "RELATED-TO" relparam ":"
	( uid / ; for VALUE=UID
	uri / ; for VALUE=URI
	text ) ; for VALUE=TEXT or default
	CRLF
	relparam = ; the elements herein may appear in any order,		related = "RELATED-TO" relparam ":"
	; and the order is not significant.		( uid / ; for VALUE=UID
	[";" "VALUE" "=" ("UID" /		uri / ; for VALUE=URI
	"URI" /		text ) ; for VALUE=TEXT or default
	"TEXT")]		CRLF
	[";" reltypeparam]
	[";" gapparam]
	*(";" other-param)
	Example:		relparam = ; the elements herein may appear in any order,
			; and the order is not significant.
			[";" "VALUE" "=" ("UID" /
			"URI" /
			"TEXT")]
			[";" reltypeparam]
			[";" gapparam]
			*(";" other-param)
	The following are examples of this property.		Example: The following are examples of this property.
	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:
	http://example.com/caldav/user/jb/cal/		http://example.com/caldav/user/jb/cal/
	19960401-080045-4000F192713.ics		19960401-080045-4000F192713.ics
	10. Security Considerations		10. Security Considerations
	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 [RFC3986] for a		entailed in using the URIs provided as values. See section 7 of
	discussion of the security considerations relating to URIs.		[RFC3986] for a discussion of the security considerations relating to
			URIs.
			In particular note section 7.1 "Reliability and Consistency" of
			[RFC3986] which points out the lack of a stability guarantee for
			referenced resources.
			When the value is a REFERENCE type the targeted data is an XML
			document or portion thereof. Consumers need to be aware of the
			security issues related to XML processing - in particular those
			related to XML entities. See [RFC4918] - Section 20.6. 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 property have the same issues in
	that values may be URIs.		that values may be URIs.
	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 [RFC5545]
	IANA has also added a reference to this document where the properties		IANA has also added a reference to this document where the properties
	originally defined in [RFC5545] have been updated by this document.		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 |		+------------+---------+------------------------+
	| REFID | Current | Section 8.3 |		| LINK | Current | Section 8.2 |
	| RELATED-TO | Current | [RFC5545], Section 9 |		+------------+---------+------------------------+
	+------------+---------+----------------------+		| REFID | Current | Section 8.3 |
			+------------+---------+------------------------+
			| RELATED-TO | Current | [RFC5545], Section 9.1 |
			+------------+---------+------------------------+
			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 |
	| REL | Current | Section 6.1 |
	+-----------+---------+-------------+		+-----------+---------+-------------+
			| LINKREL | Current | Section 6.1 |
			+-----------+---------+-------------+
			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 |
	+-----------------+---------+-----------+		+=================+=========+===========+
	| REFERENCE | Current | Section 7 |		| REFERENCE | Current | Section 7 |
			+-----------------+---------+-----------+
	| UID | Current | Section 7 |		| UID | Current | Section 7 |
	+-----------------+---------+-----------+		+-----------------+---------+-----------+
			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 |
			+-------------------+---------+-----------+
	| FINISHTOSTART | Current | Section 4 |		| FINISHTOSTART | Current | Section 4 |
			+-------------------+---------+-----------+
	| FIRST | Current | Section 5 |		| FIRST | Current | Section 5 |
			+-------------------+---------+-----------+
	| 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
	11.5. New Reference Type Registration		11.5. New Reference Type Registration
	The following link relation values have been added to the Reference		The following link relation values have been added to the Reference
	Types Registry defined in Section 6.2.2 of [RFC8288]		Types Registry defined in Section 6.2.2 of [RFC8288]
			+========+=========+=============+
	+--------+---------+-------------+
	| Name | Status | Reference |		| Name | Status | Reference |
	+--------+---------+-------------+		+========+=========+=============+
	| SOURCE | Current | Section 6.1 |		| SOURCE | Current | Section 6.1 |
	+--------+---------+-------------+		+--------+---------+-------------+
			Table 5
	12. Acknowledgements		12. Acknowledgements
	The author would like to thank the members of the Calendaring and		The author would like to thank the members of the Calendaring and
	Scheduling Consortium technical committees and the following		Scheduling Consortium technical committees and the following
	individuals for contributing their ideas, support and comments:		individuals for contributing their ideas, support and comments:
	Adrian Apthorp, Cyrus Daboo, Marten Gajda, Ken Murchison		Adrian Apthorp, Cyrus Daboo, Marten Gajda, Ken Murchison
	The author would also like to thank CalConnect, the Calendaring and		The author would also like to thank CalConnect, the Calendaring and
	Scheduling Consortium for advice with this specification.		Scheduling Consortium for advice with this specification.
	skipping to change at page 17, line 12 ¶		skipping to change at page 18, line 39 ¶
	Attachments", RFC 8607, DOI 10.17487/RFC8607, June 2019,		Attachments", RFC 8607, DOI 10.17487/RFC8607, June 2019,
	<https://www.rfc-editor.org/info/rfc8607>.		<https://www.rfc-editor.org/info/rfc8607>.
	13.2. Normative References		13.2. 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
			Resource Identifier (URI): Generic Syntax", STD 66,
			RFC 3986, DOI 10.17487/RFC3986, January 2005,
			<https://www.rfc-editor.org/info/rfc3986>.
			[RFC4918] Dusseault, L., Ed., "HTTP Extensions for Web Distributed
			Authoring and Versioning (WebDAV)", RFC 4918,
			DOI 10.17487/RFC4918, June 2007,
			<https://www.rfc-editor.org/info/rfc4918>.
	[RFC5545] Desruisseaux, B., Ed., "Internet Calendaring and		[RFC5545] Desruisseaux, B., Ed., "Internet Calendaring and
	Scheduling Core Object Specification (iCalendar)",		Scheduling Core Object Specification (iCalendar)",
	RFC 5545, DOI 10.17487/RFC5545, September 2009,		RFC 5545, DOI 10.17487/RFC5545, September 2009,
	<https://www.rfc-editor.org/info/rfc5545>.		<https://www.rfc-editor.org/info/rfc5545>.
	[RFC7986] Daboo, C., "New Properties for iCalendar", RFC 7986,		[RFC7986] Daboo, C., "New Properties for iCalendar", RFC 7986,
	DOI 10.17487/RFC7986, October 2016,		DOI 10.17487/RFC7986, October 2016,
	<https://www.rfc-editor.org/info/rfc7986>.		<https://www.rfc-editor.org/info/rfc7986>.
	[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", World Wide Web Consortium
	Recommendation REC-skos-reference-20090818, August 2009,		Recommendation REC-skos-reference-20090818, 18 August
			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]
			Grosso, P., Maler, E., Marsh, J., and N. Walsh, "XPointer
			Framework", World Wide Web Consortium Recommendation REC-
			xptr-framework-20030325, 25 March 2003,
			<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., Daniel, R., and E. Maler, "XPointer xpointer()
	Scheme", World Wide Web Consortium WD WD-xptr-xpointer-		Scheme", World Wide Web Consortium WD WD-xptr-xpointer-
	20021219, December 2002,		20021219, 19 December 2002,
	<http://www.w3.org/TR/2002/WD-xptr-xpointer-20021219>.		<http://www.w3.org/TR/2002/WD-xptr-xpointer-20021219>.
	Author's Address		Author's Address
	Michael Douglass		Michael Douglass
	Bedework		Bedework
	226 3rd Street		226 3rd Street
	Troy, NY 12180		Troy, NY 12180
	USA		United States of America
	Email: mdouglass@bedework.com		Email: mdouglass@bedework.com
	URI: http://bedework.com		URI: http://bedework.com
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