draft-ietf-calext-rscale-01.txt		draft-ietf-calext-rscale-02.txt
	Network Working Group C. Daboo		Network Working Group C. Daboo
	Internet-Draft Apple Inc.		Internet-Draft Apple Inc.
	Updates: 5545, 5546, 4791 (if approved) G. Yakushev		Updates: 4791, 5545, 5546, 6321, 7265 G. Yakushev
	Intended status: Standards Track Google Inc.		(if approved) Google Inc.
	Expires: May 15, 2015 November 11, 2014		Intended status: Standards Track December 10, 2014
			Expires: June 13, 2015
	Non-Gregorian Recurrence Rules in iCalendar		Non-Gregorian Recurrence Rules in iCalendar
	draft-ietf-calext-rscale-01		draft-ietf-calext-rscale-02
	Abstract		Abstract
	This document defines how non-Gregorian recurrence rules can be		This document defines how non-Gregorian recurrence rules can be
	specified and used in iCalendar data, and with CalDAV servers.		specified and used in iCalendar data, and with CalDAV servers.
	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.
	skipping to change at page 1, line 32		skipping to change at page 1, line 33
	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 http://datatracker.ietf.org/drafts/current/.		Drafts is at http://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 May 15, 2015.		This Internet-Draft will expire on June 13, 2015.
	Copyright Notice		Copyright Notice
	Copyright (c) 2014 IETF Trust and the persons identified as the		Copyright (c) 2014 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
	(http://trustee.ietf.org/license-info) in effect on the date of		(http://trustee.ietf.org/license-info) in effect on the date of
	publication of this document. Please review these documents		publication of this document. Please review these documents
	skipping to change at page 2, line 15		skipping to change at page 2, line 15
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	2. Conventions Used in This Document . . . . . . . . . . . . . . 3		2. Conventions Used in This Document . . . . . . . . . . . . . . 3
	3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4		3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4
	4. Extended RRULE Property . . . . . . . . . . . . . . . . . . . 5		4. Extended RRULE Property . . . . . . . . . . . . . . . . . . . 5
	4.1. Handling Leap Months . . . . . . . . . . . . . . . . . . 6		4.1. Handling Leap Months . . . . . . . . . . . . . . . . . . 6
	4.2. Examples . . . . . . . . . . . . . . . . . . . . . . . . 7		4.2. Examples . . . . . . . . . . . . . . . . . . . . . . . . 7
	5. Registering Calendar Systems . . . . . . . . . . . . . . . . 9		5. Registering Calendar Systems . . . . . . . . . . . . . . . . 9
	6. Use with iTIP . . . . . . . . . . . . . . . . . . . . . . . . 10		6. Use with iTIP . . . . . . . . . . . . . . . . . . . . . . . . 10
	7. Use with CalDAV . . . . . . . . . . . . . . . . . . . . . . . 11		7. Use with xCal . . . . . . . . . . . . . . . . . . . . . . . . 11
	7.1. CALDAV:supported-rscale-set Property . . . . . . . . . . 11		8. Use with jCal . . . . . . . . . . . . . . . . . . . . . . . . 11
	8. Security Considerations . . . . . . . . . . . . . . . . . . . 12		9. Use with CalDAV . . . . . . . . . . . . . . . . . . . . . . . 12
	9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12		9.1. CALDAV:supported-rscale-set Property . . . . . . . . . . 13
	10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12		10. Security Considerations . . . . . . . . . . . . . . . . . . . 14
	11. References . . . . . . . . . . . . . . . . . . . . . . . . . 12		11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
	11.1. Normative References . . . . . . . . . . . . . . . . . . 12		12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14
	11.2. Informative References . . . . . . . . . . . . . . . . . 13		13. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
			13.1. Normative References . . . . . . . . . . . . . . . . . . 14
			13.2. Informative References . . . . . . . . . . . . . . . . . 15
	Appendix A. Change History (To be removed by RFC Editor before		Appendix A. Change History (To be removed by RFC Editor before
	publication) . . . . . . . . . . . . . . . . . . . . 13		publication) . . . . . . . . . . . . . . . . . . . . 15
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15		Appendix B. xCal RELAX NG schema update . . . . . . . . . . . . 16
			Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
	1. Introduction		1. Introduction
	The iCalendar [RFC5545] data format is in widespread use to represent		The iCalendar [RFC5545] data format is in widespread use to represent
	calendar data. iCalendar represents dates and times using the		calendar data. iCalendar represents dates and times using the
	Gregorian calendar system only. It does provide a way to use non-		Gregorian calendar system only. It does provide a way to use non-
	Gregorian calendar systems via a "CALSCALE" property, but this has		Gregorian calendar systems via a "CALSCALE" property, but this has
	never been used. However, there is a need to support at least non-		never been used. However, there is a need to support at least non-
	Gregorian recurrence patterns to cover anniversaries, and many local,		Gregorian recurrence patterns to cover anniversaries, and many local,
	religious, or civil holidays based on non-Gregorian dates.		religious, or civil holidays based on non-Gregorian dates.
	skipping to change at page 3, line 21		skipping to change at page 3, line 24
	calendar systems to be used. With this, all the date, time and		calendar systems to be used. With this, all the date, time and
	period values in the iCalendar object would remain specified using		period values in the iCalendar object would remain specified using
	the Gregorian calendar system, but repeating patterns in other		the Gregorian calendar system, but repeating patterns in other
	calendar systems could be defined. It is then up to calendar user		calendar systems could be defined. It is then up to calendar user
	agents and servers to map between Gregorian and non-Gregorian		agents and servers to map between Gregorian and non-Gregorian
	calendar systems in order to expand out recurrence instances.		calendar systems in order to expand out recurrence instances.
	This specification does not itself define calendar systems, rather it		This specification does not itself define calendar systems, rather it
	utilizes the calendar system registry defined by the Unicode		utilizes the calendar system registry defined by the Unicode
	Consortium in their CLDR (Common Locale Data Repository) project		Consortium in their CLDR (Common Locale Data Repository) project
	[UNICODE.CLDR].		[UNICODE.CLDR], as implemented in the Unicode (ICU) Library
			[UNICODE.ICU].
	2. Conventions Used in This Document		2. 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		"OPTIONAL" in this document are to be interpreted as described in
	[RFC2119].		[RFC2119].
	The notation used in this memo is the ABNF notation of [RFC5234] as		The notation used in this memo is the ABNF notation of [RFC5234] as
	used by iCalendar [RFC5545]. Any syntax elements shown below that		used by iCalendar [RFC5545]. Any syntax elements shown below that
	skipping to change at page 11, line 5		skipping to change at page 11, line 5
	the iTIP message SHOULD be rejected, returning a "REQUEST-STATUS"		the iTIP message SHOULD be rejected, returning a "REQUEST-STATUS"
	property set to the "3.1" status code (as per Section 3.6.14 of		property set to the "3.1" status code (as per Section 3.6.14 of
	[RFC5546]).		[RFC5546]).
	if the iTIP message is accepted and the calendar component treated		if the iTIP message is accepted and the calendar component treated
	as non-recurring, an iTIP reply with a "REQUEST-STATUS" property		as non-recurring, an iTIP reply with a "REQUEST-STATUS" property
	set to the "2.8" or "2.10" status codes (as per Sections 3.6.9 or		set to the "2.8" or "2.10" status codes (as per Sections 3.6.9 or
	3.6.11, respectively, of [RFC5546]) SHOULD be returned.		3.6.11, respectively, of [RFC5546]) SHOULD be returned.
	7. Use with CalDAV		7. Use with xCal
			xCal [RFC6321] defines how iCalendar data is represented in XML.
			This specification extends the <recur> XML element in Section 3.6.10
			of [RFC6321] in the following manner:
			1. A new <rscale> XML element is defined as a child element of
			<recur>. The content of this element MUST be a string whose
			value is the "RSCALE" element value of the "RRULE", with case
			preserved.
			2. A new <skip> XML element is defined as a child element of
			<recur>. The content of this element MUST be a string whose
			value is the "SKIP" element value of the "RRULE", with case
			preserved.
			3. The "bymonth" XML element is redefined to support either numeric
			or string values as its content (as per Section 4.1).
			Extensions to the RELAX NG schema in Appendix A of [RFC6321] are
			defined in Appendix B.
			Example: the iCalendar "RRULE" property:
			RRULE:RSCALE=GREGORIAN;FREQ=YEARLY;SKIP=FORWARD
			would be represented in XML as:
			<rrule>
			<recur>
			<rscale>GREGORIAN</rscale>
			<freq>YEARLY</freq>
			<skip>FORWARD</skip>
			</recur>
			</rrule>
			8. Use with jCal
			jCal [RFC7265] defines how iCalendar data is represented in JSON.
			This specification extends the "recur" JSON object defined in
			Section 3.6.10 of [RFC7265] in the following manner:
			1. A new "rscale" child member is defined. This MUST be a string
			whose value is the "RSCALE" element value of the "RRULE", with
			case preserved.
			2. A new "skip" child member is defined. This MUST be a string
			whose value is the "SKIP" element value of the "RRULE", with case
			preserved.
			3. The "bymonth" child member is redefined to support either numeric
			or string values. If the "BYMONTH" element value is an integer,
			then a numeric JSON value MUST be used. If the "BYMONTH" element
			value is an integer with the "L" suffix (as per Section 4.1),
			then a JSON string value MUST be used.
			Example: the iCalendar "RRULE" property:
			RRULE:RSCALE=GREGORIAN;FREQ=YEARLY;SKIP=FORWARD
			would be represented in JSON as:
			[
			"rrule",
			{},
			"recur",
			{
			"rscale": "GREGORIAN",
			"freq": "YEARLY",
			"skip": "FORWARD"
			}
			]
			9. Use with CalDAV
	The CalDAV [RFC4791] calendar access protocol allows clients and		The CalDAV [RFC4791] calendar access protocol allows clients and
	servers to exchange iCalendar data. In addition, CalDAV clients are		servers to exchange iCalendar data. In addition, CalDAV clients are
	able to query calendar data stored on the server, including time-		able to query calendar data stored on the server, including time-
	based queries. Since an "RSCALE" element value determines the time		based queries. Since an "RSCALE" element value determines the time
	ranges for recurring instances in a calendar component, CalDAV		ranges for recurring instances in a calendar component, CalDAV
	servers need to support it to interoperate with clients also using		servers need to support it to interoperate with clients also using
	the "RSCALE" element.		the "RSCALE" element.
	A CalDAV server advertises a CALDAV:supported-rscale-set WebDAV		A CalDAV server advertises a CALDAV:supported-rscale-set WebDAV
	skipping to change at page 11, line 41		skipping to change at page 13, line 21
	attempts to store iCalendar data with an "RSCALE" element value not		attempts to store iCalendar data with an "RSCALE" element value not
	supported by the server.		supported by the server.
	It is possible for an "RSCALE" value to be present in calendar data		It is possible for an "RSCALE" value to be present in calendar data
	on the server being accessed by a client that does not support an		on the server being accessed by a client that does not support an
	"RSCALE" element or its specified value. It is expected that		"RSCALE" element or its specified value. It is expected that
	existing clients, unaware of "RSCALE", will fail gracefully by		existing clients, unaware of "RSCALE", will fail gracefully by
	ignoring the calendar component, whilst still processing other		ignoring the calendar component, whilst still processing other
	calendar data on the server.		calendar data on the server.
	7.1. CALDAV:supported-rscale-set Property		9.1. CALDAV:supported-rscale-set Property
	Name: supported-rscale-set		Name: supported-rscale-set
	Namespace: urn:ietf:params:xml:ns:caldav		Namespace: urn:ietf:params:xml:ns:caldav
	Purpose: Enumerates the set of supported iCalendar "RSCALE" element		Purpose: Enumerates the set of supported iCalendar "RSCALE" element
	values supported by the server.		values supported by the server.
	Protected: This property MUST be protected and SHOULD NOT be		Protected: This property MUST be protected and SHOULD NOT be
	returned by a PROPFIND allprop request (as defined in Section 14.2		returned by a PROPFIND allprop request (as defined in Section 14.2
	skipping to change at page 12, line 25		skipping to change at page 14, line 5
	<C:supported-rscale-set		<C:supported-rscale-set
	xmlns:C="urn:ietf:params:xml:ns:caldav">		xmlns:C="urn:ietf:params:xml:ns:caldav">
	<C:supported-rscale>GREGORIAN</C:supported-rscale>		<C:supported-rscale>GREGORIAN</C:supported-rscale>
	<C:supported-rscale>CHINESE</C:supported-rscale>		<C:supported-rscale>CHINESE</C:supported-rscale>
	<C:supported-rscale>ISLAMIC-CIVIL</C:supported-rscale>		<C:supported-rscale>ISLAMIC-CIVIL</C:supported-rscale>
	<C:supported-rscale>HEBREW</C:supported-rscale>		<C:supported-rscale>HEBREW</C:supported-rscale>
	<C:supported-rscale>ETHIOPIC</C:supported-rscale>		<C:supported-rscale>ETHIOPIC</C:supported-rscale>
	</C:supported-rscale-set>		</C:supported-rscale-set>
	8. Security Considerations		10. Security Considerations
	This specification does not introduce any addition security concerns		This specification does not introduce any addition security concerns
	beyond those described in [RFC5545], [RFC5546], and [RFC4791].		beyond those described in [RFC5545], [RFC5546], and [RFC4791].
	9. IANA Considerations		11. IANA Considerations
	This document requires no IANA actions.		This document requires no IANA actions.
	10. Acknowledgments		12. Acknowledgments
	Thanks to the following for feedback: Mark Davis, Mike Douglass,		Thanks to the following for feedback: Mark Davis, Mike Douglass,
	Peter Edberg, Marten Gajda, Ken Murchison, Arnaud Quillaud, Dave		Peter Edberg, Marten Gajda, Philipp Kewisch, Ken Murchison, Arnaud
	Thewlis, and Umaoka Yoshito.		Quillaud, Dave Thewlis, and Umaoka Yoshito.
	This specification originated from work at the Calendaring and		This specification originated from work at the Calendaring and
	Scheduling Consortium, which has helped with the development and		Scheduling Consortium, which has helped with the development and
	testing of implementations.		testing of implementations.
	11. References		13. References
	11.1. Normative References		13.1. 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, March 1997.		Requirement Levels", BCP 14, RFC 2119, March 1997.
	[RFC4791] Daboo, C., Desruisseaux, B., and L. Dusseault,		[RFC4791] Daboo, C., Desruisseaux, B., and L. Dusseault,
	"Calendaring Extensions to WebDAV (CalDAV)", RFC 4791,		"Calendaring Extensions to WebDAV (CalDAV)", RFC 4791,
	March 2007.		March 2007.
	[RFC4918] Dusseault, L., "HTTP Extensions for Web Distributed		[RFC4918] Dusseault, L., "HTTP Extensions for Web Distributed
	Authoring and Versioning (WebDAV)", RFC 4918, June 2007.		Authoring and Versioning (WebDAV)", RFC 4918, June 2007.
	skipping to change at page 13, line 23		skipping to change at page 14, line 49
	Specifications: ABNF", STD 68, RFC 5234, January 2008.		Specifications: ABNF", STD 68, RFC 5234, January 2008.
	[RFC5545] Desruisseaux, B., "Internet Calendaring and Scheduling		[RFC5545] Desruisseaux, B., "Internet Calendaring and Scheduling
	Core Object Specification (iCalendar)", RFC 5545,		Core Object Specification (iCalendar)", RFC 5545,
	September 2009.		September 2009.
	[RFC5546] Daboo, C., "iCalendar Transport-Independent		[RFC5546] Daboo, C., "iCalendar Transport-Independent
	Interoperability Protocol (iTIP)", RFC 5546, December		Interoperability Protocol (iTIP)", RFC 5546, December
	2009.		2009.
			[RFC6321] Daboo, C., Douglass, M., and S. Lees, "xCal: The XML
			Format for iCalendar", RFC 6321, August 2011.
			[RFC7265] Kewisch, P., Daboo, C., and M. Douglass, "jCal: The JSON
			Format for iCalendar", RFC 7265, May 2014.
	[UNICODE.CLDR]		[UNICODE.CLDR]
	"CLDR calendar.xml Data", Unicode Consortium CLDR,		"CLDR calendar.xml Data", Unicode Consortium CLDR,
	<http://www.unicode.org/repos/cldr/tags/latest/common/		<http://www.unicode.org/repos/cldr/tags/latest/common/
	bcp47/calendar.xml>.		bcp47/calendar.xml>.
	11.2. Informative References		13.2. Informative References
	[ISO.8601.2004]		[ISO.8601.2004]
	International Organization for Standardization, "Data		International Organization for Standardization, "Data
	elements and interchange formats - Information interchange		elements and interchange formats - Information interchange
	- Representation of dates and times", ISO Standard 8601,		- Representation of dates and times", ISO Standard 8601,
	2004.		2004.
	[UNICODE.ICU]		[UNICODE.ICU]
	"International Components for Unicode", Unicode Consortium		"International Components for Unicode", Unicode Consortium
	ICU, April 2014, <http://site.icu-project.org>.		ICU, April 2014, <http://site.icu-project.org>.
	Appendix A. Change History (To be removed by RFC Editor before		Appendix A. Change History (To be removed by RFC Editor before
	publication)		publication)
			Changes in draft-ietf-calext-rscale-02:
			1. Added xCal and jCal changes sections and relax NG schema
			appendix.
			2. Added ICU reference at the end of Section 1.
	Changes in draft-ietf-calext-rscale-01:		Changes in draft-ietf-calext-rscale-01:
	1. Editorial changes/fixes per document shepherd review.		1. Editorial changes/fixes per document shepherd review.
	2. Switched CLDR reference to "tags/latest".		2. Switched CLDR reference to "tags/latest".
	Changes in draft-ietf-calext-rscale-00:		Changes in draft-ietf-calext-rscale-00:
	1. Updated some references.		1. Updated some references.
	skipping to change at page 15, line 5		skipping to change at page 16, line 41
	3. Clarified when SKIP processing occurs.		3. Clarified when SKIP processing occurs.
	Changes in draft-daboo-icalendar-rscale-01:		Changes in draft-daboo-icalendar-rscale-01:
	1. Removed requirement that RSCALE be the first item in an RRULE.		1. Removed requirement that RSCALE be the first item in an RRULE.
	2. Added BYLEAPMONTH element and removed BYMONTH "L" suffix.		2. Added BYLEAPMONTH element and removed BYMONTH "L" suffix.
	3. Removed Open Issues.		3. Removed Open Issues.
	Authors' Addresses		Appendix B. xCal RELAX NG schema update
			The following changes are made to the RELAX NG schema defined in
			Appendix A of [RFC6321].
			# 3.3.10 RECUR
			# This extension adds type-rscale and type-skip,
			# and modifies type-bymonth
			value-recur = element recur {
			type-rscale?,
			type-freq,
			(type-until | type-count)?,
			element interval {
			xsd:positiveInteger
			}?,
			type-bysecond*,
			type-byminute*,
			type-byhour*,
			type-byday*,
			type-bymonthday*,
			type-byyearday*,
			type-byweekno*,
			type-bymonth*,
			type-bysetpos*,
			element wkst { type-weekday }?,
			type-skip?
			}
			type-rscale = element rscale {
			xsd:string
			}
			type-bymonth = element bymonth {
			xsd:positiveInteger |
			xsd:string
			}
			type-skip = element skip {
			"YES" |
			"BACKWARD" |
			"FORWARD"
			}
			Authors' Addresses
	Cyrus Daboo		Cyrus Daboo
	Apple Inc.		Apple Inc.
	1 Infinite Loop		1 Infinite Loop
	Cupertino, CA 95014		Cupertino, CA 95014
	USA		USA
	Email: cyrus@daboo.name		Email: cyrus@daboo.name
	URI: http://www.apple.com/		URI: http://www.apple.com/
	Gregory Yakushev		Gregory Yakushev
End of changes. 19 change blocks.
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