Internet DRAFT - draft-douglass-icalendar-series
draft-douglass-icalendar-series
Network Working Group M. Douglass
Internet-Draft Spherical Cow Group
Updates: 5545 (if approved) February 15, 2017
Intended status: Standards Track
Expires: August 19, 2017
Support for Series in iCalendar
draft-douglass-icalendar-series-00
Abstract
This specification updates [RFC5545] by defining a new repeating set
of events known as a series. This differs from recurrences in that
each instance is a separate entity with a parent relationship to a
specified template entity.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on August 19, 2017.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Overrides and iCalendar recurrences . . . . . . . . . . . . . 3
2.1. Changing the master start or the recurrence rules . . . . 3
2.2. Splitting recurrences . . . . . . . . . . . . . . . . . . 3
3. Series . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Modifying series patterns and splitting . . . . . . . . . 5
3.2. The series master . . . . . . . . . . . . . . . . . . . . 5
3.3. The series instances . . . . . . . . . . . . . . . . . . 5
4. Redefined Relation Type Value . . . . . . . . . . . . . . . . 6
5. New Property Parameters . . . . . . . . . . . . . . . . . . . 8
5.1. Split . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.2. Lookahead count . . . . . . . . . . . . . . . . . . . . . 9
5.3. Lookahead period . . . . . . . . . . . . . . . . . . . . 9
6. New Properties . . . . . . . . . . . . . . . . . . . . . . . 10
6.1. Generating Series members . . . . . . . . . . . . . . . . 10
6.2. Series UID . . . . . . . . . . . . . . . . . . . . . . . 12
6.3. Series-exception-date . . . . . . . . . . . . . . . . . . 12
6.4. Series-date . . . . . . . . . . . . . . . . . . . . . . . 13
6.5. Series-id . . . . . . . . . . . . . . . . . . . . . . . . 15
6.6. Last series id . . . . . . . . . . . . . . . . . . . . . 16
6.7. Series Rule . . . . . . . . . . . . . . . . . . . . . . . 19
7. Redefined RELATED-TO Property . . . . . . . . . . . . . . . . 20
7.1. RELATED-TO . . . . . . . . . . . . . . . . . . . . . . . 20
8. Backwards compatibility . . . . . . . . . . . . . . . . . . . 22
9. CalDAV extensions . . . . . . . . . . . . . . . . . . . . . . 23
10. Security Considerations . . . . . . . . . . . . . . . . . . . 23
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
11.1. iCalendar Property Registrations . . . . . . . . . . . . 23
11.2. iCalendar Property Parameter Registrations . . . . . . . 23
11.3. iCalendar RELTYPE Value Registrations . . . . . . . . . 24
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 24
13. Normative References . . . . . . . . . . . . . . . . . . . . 24
Appendix A. Points for discussion . . . . . . . . . . . . . . . 25
Appendix B. Change log . . . . . . . . . . . . . . . . . . . . . 26
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 26
1. Introduction
Since iCalendar was first defined there has been only one way to
express a repeating set of events - the recurrence. This defined a
master event, a set of rules for computing the instances and a way of
overriding certain instances.
This approach works well enough in certain situations but has many
problems which need to be addressed.
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This specification introduces a new approach to repeating patterns of
entities which avoids some of the problems.
2. Overrides and iCalendar recurrences
The recurrence rules specify how instances are to be computed. These
rules provide a set of keys - the RECURRENCE-ID - and an instance can
be created with the calculated start date/time and a copy of the
duration (or calculated end date/time).
The specification allows for overrides. These are handled by
supplying a complete replacement for the instance with a RECURRENCE-
ID property matching that of the instance being overridden. This may
change any of the properties (except the UID) - including start, end
or duration.
If a long lived recurrence is heavily overridden it becomes very
cumbersome. The master plus overrides is considered a single
resource in most circumstances (iTip allows the delivery of a single
instance in certain situations).
Simple meetings can become heavily modifed recurrences through adding
the weeks agenda to the description, changing of attendees etc.
There are approaches being considered to mitigate some of these
issues which mostly involve only storing changes but recurrences are
still awkward to deal with.
2.1. Changing the master start or the recurrence rules
This can lead to some very difficult problems to resolve. In the
case of a heavily modified meeting it may be difficult to impossible
to determine which override applies to the newly modified event.
For example, a weekly book-reading is moved from Monday to Friday.
There are weeks of scheduled events in the future. Do we move them
all forward to the next instance or skip one and move them back? If
it becomes bi-weekly rather than weekly do we drop every other or
just space them out more?
To be sure - some of these problems are not totally resolved by a
series approach but they become more tractable.
2.2. Splitting recurrences
The [RFC5545] THISANDFUTURE range is poorly supported. Splitting is
what a number of implementations use to avoid changing overrrides in
the past.
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The recurring event is split into 2, one being the truncated original
the other being a new recurring event starting at the time of the
THISANDFUTURE override.
There is left the problem of relating the two, this can be
accomplished by use of the RELATED-TO property but that is not
standardized.
3. Series
A series is a, generally regularly, repeating sets of events or tasks
each instance of which is usually, but not always, different in some
respect. Examples may be a library running an after-school reading
program which usually, takes place at the same time each week but
always differs in the book or author being studied.
In recurrences an instances is a calculated 'virtual' object, unless
overridden. It has the same UID as the master and a RECURRENCE-ID
which is always one of the calculated set.
In a series, a specified number of instances are created ahead of
time each with their own unique UID. They are all related to the
master using a SERIES-MASTER relation type defined in this
specification. Each instance acts as an individual component as far
as retrieval and searching is concerned.
Each instance and master is identified as a member of the full series
by the SERIES-UID property. The value of this property is the same
in all members of the series even when splits have occurred.
As instances are created a LAST-SERIES-ID property is added or
updated in the master to indicate which instance was last created.
When there are SXDATE properties this property value may represent an
instance which cannot be created. It merely represents the latest
calculated date.
This property allows generated instances to be deleted without the
addition of SXDATE properties to the master. The SXDATE only
indicates future instances which MUST NOT be created.
As time goes on more instances are created either by the server or by
a client when it inspects the current state of the series. The
number of instances may be based on time or a count.
For example, an organization may allow rooms to be booked only 4
weeks ahead. Thus a series may be set up which has that 4 week set
of events in the future. Each will have the room as an attendee
ensuring that at least the room is booked at the regular time.
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3.1. Modifying series patterns and splitting
If it becomes necessary to modify the series rules or the master
start then the series is always split at the point of the
modification.
When a series is split the previous master is modifed to truncate the
current series at the last generated instance and a parameter
SPLIT=YES is added to the series rule to indicate that this master is
now split.
The split may result in a number of instances related to the old
series but overlapping the new. It is up to the implementation to
decide what should be done with these but this usually requires a
degree of interaction with a human (or very intelligent robot). The
application may offer to copy them into the corresponding new
instances - if these can be easily determined, offer to delete all of
them or let the user manually copy information and delete.
The new series master is related to the old master by the new series
master having a RELATED-TO property with RELTYPE=SERIES-MASTER
pointing at the previous master. In that way a backwards chain of
series masters may be created
3.2. The series master
A series master is identified in much the same way as a recurrence
master. It will contain an SRULE and 0 or more SDATE properties or 1
or more SDATE properties. Additionally it may contain 0 or more
SXDATE properties to exclude instances.
As noted above, if the series was split it may contain a RELATED-TO
property with RELTYPE=SERIES-MASTER and a value of the previous
series master.
The master will also contain a LAST-SERIES-ID if any instances have
been calculated and perhaps generated.
It is important to note that the series master is the first member of
the series. Thus the first instance always occurs AFTER the series
master.
3.3. The series instances
A series instance is identified by having a SERIES-ID property which
is calculated in the same manner as a RECURRENCE-ID. It MUST also
contain a RELATED-TO property with RELTYPE=SERIES-MASTER and a value
being the UID of the series master.
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As noted above, if the series was split it may contain a RELATED-TO
property with RELTYPE=SERIES-MASTER and a value being the UID of the
previous series master.
4. Redefined Relation Type Value
Relationship parameter type values are defined in section 3.2.15. of
[RFC5545]. This specification augments that parameter to include the
new relationship values SERIES-MASTER
Format Definition:
This property parameter is respecified as follows:
reltypeparam = "RELTYPE" "="
("PARENT" ; Parent relationship - Default
/ "CHILD" ; Child relationship
/ "SIBLING" ; Sibling relationship
/ "DEPENDS-ON" ; refers to previous task
/ "REFID" ; Relationship based on REFID
/ "STRUCTURED-CATEGORY"
; Relationship based on STRUCTURED-CATEGORY
/ "FINISHTOSTART" ; Temporal relationship
/ "FINISHTOFINISH" ; Temporal relationship
/ "STARTTOFINISH" ; Temporal relationship
/ "STARTTOSTART" ; Temporal relationship
/ "SERIES-MASTER" ; link to the master component
/ iana-token ; Some other IANA-registered
; iCalendar relationship type
/ x-name) ; A non-standard, experimental
; relationship type
Description: This parameter can be specified on a property that
references another related calendar component. The parameter may
specify the hierarchical relationship type of the calendar
component referenced by the property when the value is PARENT,
CHILD or SIBLING. If this parameter is not specified on an
allowable property, the default relationship type is PARENT.
Applications MUST treat x-name and iana-token values they don't
recognize the same way as they would the PARENT value.
This parameter defines the temporal relationship when the value is
one of the project management standard relationships
FINISHTOSTART, FINISHTOFINISH, STARTTOFINISH or STARTTOSTART.
This property will be present in the predecessor entity and will
refer to the successor entity. The GAP parameter specifies the
lead or lag time between the predecessor and the successor. In
the description of each temporal relationship below we refer to
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Task-A which contains and controls the relationship and Task-B the
target of the relationship.
RELTYPE=PARENT: See [RFC5545] section 3.2.15.
RELTYPE=CHILD: See [RFC5545] section 3.2.15.
RELTYPE=SIBLING: See [RFC5545] section 3.2.15.
RELTYPE=DEPENDS-ON: Indicates that the current calendar component
depends on the referenced calendar component in some manner. For
example a task may be blocked waiting on the other, referenced,
task.
RELTYPE=REFID: Establishes a reference from the current component to
components with a REFID property which matches the value given in
the associated RELATED-TO property.
RELTYPE=SERIES-MASTER: Indicates that the current calendar component
is bsed on the referenced calendar component. The value is a UID.
RELTYPE=STRUCTURED-CATEGORY: Establishes a reference from the
current component to components with a STRUCTURED-CATEGORY
property which matches the value given in the associated RELATED-
TO property.
RELTYPE=FINISHTOSTART: Task-B cannot start until Task-A finishes.
For example, when sanding is complete, painting can begin.
============
| Task-A |--+
============ |
|
V
============
| Task-B |
============
Figure 1: Finish to start relationship
RELTYPE=FINISHTOFINISH: Task-B cannot finish before Task-A is
finished, that is the end of Task-A defines the end of Task-B.
For example, we start the potatoes, then the meat then the peas
but they should all be cooked at the same time.
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============
| Task-A |--+
============ |
|
============ |
| Task-B |<-+
============
Figure 2: Finish to finish relationship
RELTYPE=STARTTOFINISH: The start of Task-A (which occurs after Task-
B) controls the finish of Task-B. For example, ticket sales
(Task-B) end when the game starts (Task-A).
============
+--| Task-A |
| ============
|
============ |
| Task-B |<-+
============
Figure 3: Start to finish relationship
RELTYPE=STARTTOSTART: The start of Task-A triggers the start of
Task-B, that is Task-B can start anytime after Task-A starts.
============
+--| Task-A |
| ============
|
| ============
+->| Task-B |
============
Figure 4: Start to start relationship
5. New Property Parameters
5.1. Split
Parameter name: SPLIT
Purpose: To indicate a series has been split.
Format Definition:
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This parameter is defined by the following notation:
splitparam = "SPLIT" "="
("YES" ; The series is split
/ "NO" ; The series is not split (default)
/ x-name ; Experimental reference type
/ iana-token) ; Other IANA registered type
Description: This parameter MAY be specified on the SRULE property
to indicate that the series has been split with SPLIT=YES. Once
split is is probably innapropriate to modify the series further.
5.2. Lookahead count
Parameter name: LOOKAHEAD-COUNT
Purpose: To specify the number of series instances that should be
generated in advance.
Format Definition:
This parameter is defined by the following notation:
lookahead-countparam = "LOOKAHEAD-COUNT" "=" 1*DIGIT
Description: This parameter MAY be specified on the SRULE property
to indicate how many series instances should be generated in
advance.
An implementation is free to apply its own limts but MUST NOT
generate more than those defined by this parameter and/or the
LOOKAHEAD-PERIOD parameter.
If both the LOOKAHEAD-PERIOD and LOOKAHEAD-COUNT arameters are
supplied the result should be limited by both.
For example, if the LOOKAHEAD-PERIOD parameter would cause 8
instances to be generated but LOOKAHEAD-COUNT specifies 4 then
only 4 instances will be generated.
5.3. Lookahead period
Parameter name: LOOKAHEAD-PERIOD
Purpose: To specify a maximum period for which series instances
should be generated in advance.
Format Definition:
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This parameter is defined by the following notation:
lookahead-periodparam = "LOOKAHEAD-PERIOD" "="
DQUOTE dur-value DQUOTE
Description: This parameter MAY be specified on the SRULE property
to indicate how far in advance series instances should be
generated.
An implementation is free to apply its own limts but MUST NOT
generate more than those defined by this parameter and/or the
LOOKAHEAD-COUNT parameter.
If both the LOOKAHEAD-PERIOD and LOOKAHEAD-COUNT arameters are
supplied the result should be limited by both.
For example, if the LOOKAHEAD-PERIOD parameter would cause 8
instances to be generated but LOOKAHEAD-COUNT specifies 4 then
only 4 instances will be generated.
The value is a quoted duration.
6. New Properties
The SERIES-ID, LAST-SERIES-ID, SDATE and SXDATE properties are
identical in form and in the parameters they take.
All must conform in form to the DTSTART property of the master
component. Only the SDATE may specify a time which is not part of
the calculated series.
The SRULE property vakue is identical in form to the RRULE property
defined in [RFC5545]. The LOOKAHEAD-COUNT and LOOKAHEAD-PERIOD
parameters indicate how many instances should be generated in
advance.
6.1. Generating Series members
An agent, either the server or a client, will periodically extend the
set of instances. The number of such generated instances is limited
by:
Elements of the rule: The UNTIL or COUNT parts of the rule define
when the series terminates. Thus a COUNT=100 specifies a maximum
of 100 series members.
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Lookahead count: This specifies how many series memerbs can exist
from the current date/time. Thus a LOOKAHEAD-COUNT=4 means a
maximum of 4 generated instances.
Lookahead period: This specifies how far into the future series
members can be generated. Thus a LOOKAHEAD-PERIOD="PT2M" means a
maximum period of 2 months.
System limits: This client or server SHOULD also apply limits to
prevent a series from generating an overlarge set of members.
The starting point for the calculation is the DTSTART of the master
component or the LAST-SERIES-ID if it exists in the master. In both
cases the instance represented by that date is NOT generated as part
of the intance set and the actual instance may have been excluded by
an SXDATE property but the starting date is still valid.
The starting date/time property defines the first instance in the
next batch of series members. Note that the starting property value
MUST match the pattern of the series rule, if specified. For
example, if the rule specifies every Wednesday the starting date MUST
be a Wednesday.
The end date/time of the set will be provided by the UNTIL part of
the rule, the LOOKAHEAD-PERIOD or by a system maxima.
A set of date/time values can be generated within those contraints.
As each date/time value is generated it can be ignored if it is one
of the SXDATE values.
Generation of values can terminate when the size of the result
exceeds that given by the COUNT rule element, the LOOKAHEAD-COUNT
value or any systm limit.
Any SDATE values that fall within the current range and are not in
the set of SXDATE values can be added and the result truncated again
to match the size limits.
Finally, any date/time values that have already been generated and
are present as SERIES-ID values should be removed from the set. What
remains is the new set of members to extend the current series.
The last of those values becomes the new value for the LAST-SERIES-ID
property in the series master.
As noted above the "SXDATE" property can be used to exclude the value
specified in the master. This leads to a complication as the master
needs to be preserved as a container for the values which define the
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series. This is flagged by adding a DELETED-MASTER elemeng to the
SERIES-STATUS property..
6.2. Series UID
Property name: SERIES-UID
Purpose: This property defines the persistent, globally unique
identifier for the full series.
Value Type: TEXT
Property Parameters: IANA and non-standard property parameters can
be specified on this property.
Conformance: This property MUST be specified in any "VEVENT",
"VTODO", and "VJOURNAL" calendar components acting as a series
master or series instance.
Description: The SERIES-UID MUST be globally unique. This value
SHOULD be generated by following the recommendations in section
5.3 of [RFC7986].
Format Definition:
This property is defined by the following notation:
seruid = "SERIES-UID" seruidparam ":" text CRLF
seruidparam = *(";" other-param)
Example:
The following is an example of this property:
SERIES-UID:123e4567-e89b-12d3-a456-426655440000
6.3. Series-exception-date
Property name: SXDATE
Purpose: This property defines the list of DATE-TIME exceptions for
series of events, to-dos or journal entries.
Value Type: The default value type for this property is DATE-TIME.
The value type can be set to DATE.
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Property Parameters: IANA, non-standard, value data type, and time
zone identifier property parameters can be specified on this
property.
Conformance: This property can be specified in "VEVENT", "VTODO",
and "VJOURNAL" calendar components acting as the series master.
Description: The exception dates, if specified, are used when
computing the instances of the series. They specify date/time
values which are to be removed from the set of possible series
instances.
Format Definition:
This property is defined by the following notation:
sxdate = "SXDATE" sxdtparam ":" sxdtval *("," sxdtval) CRLF
sxdtparam = *(
;
; The following are OPTIONAL,
; but MUST NOT occur more than once.
;
(";" "VALUE" "=" ("DATE-TIME" / "DATE")) /
;
(";" tzidparam) /
;
; The following is OPTIONAL,
; and MAY occur more than once.
;
(";" other-param)
;
)
sxdtval = date-time / date
;Value MUST match value type
Example:
The following is an example of this property:
SXDATE:19960402T010000Z,19960403T010000Z,19960404T010000Z
6.4. Series-date
Property name: SDATE
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Purpose: This property defines the list of DATE-TIME values for
series of events, to-dos or journal entries.
Value Type: The default value type for this property is DATE-TIME.
The value type can be set to DATE.
Property Parameters: IANA, non-standard, value data type, and time
zone identifier property parameters can be specified on this
property.
Conformance: This property can be specified in "VEVENT", "VTODO",
and "VJOURNAL" calendar components acting as the series master.
Description: This property can appear along with the "SRULE"
property to define a extra series occurrences. When they both
appear in a series master component, the instances are defined by
the union of occurrences defined by both the "SDATE" and "SRULE".
Purpose:
This property is defined by the following notation:
sdate = "SDATE" sdtparam ":" sdtval *("," sdtval) CRLF
sdtparam = *(
;
; The following are OPTIONAL,
; but MUST NOT occur more than once.
;
(";" "VALUE" "=" ("DATE-TIME" / "DATE" / "PERIOD")) /
(";" tzidparam) /
;
; The following is OPTIONAL,
; and MAY occur more than once.
;
(";" other-param)
;
)
sdtval = date-time / date
;Value MUST match value type
Example:
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The following are examples of this property:
SDATE:19970714T123000Z
SDATE;TZID=America/New_York:19970714T083000
SDATE;VALUE=PERIOD:19960403T020000Z/19960403T040000Z,
19960404T010000Z/PT3H
SDATE;VALUE=DATE:19970101,19970120,19970217,19970421
19970526,19970704,19970901,19971014,19971128,19971129,19971225
6.5. Series-id
Property name: SERIES-ID
Purpose: This property is used in conjunction with the "UID" and
"SEQUENCE" properties to identify a specific instance of a
"VEVENT", "VTODO", or "VJOURNAL" calendar component in a series.
The property value is the original value of the "DTSTART" property
of the series instance before any changes occur.
Value type: The default value type is DATE-TIME. The value type can
be set to a DATE value type. This property MUST have the same
value type as the "DTSTART" property contained within the series
component. Furthermore, this property MUST be specified as a date
with local time if and only if the "DTSTART" property contained
within the series component is specified as a date with local
time.
Property Parameters: IANA, non-standard, value data type and time
zone identifier parameters can be specified on this property.
Conformance: This property can be specified zero or more times in
any iCalendar component.
Description: The SERIES-ID is the originally calculated value of the
DTSTART property based on the master identified by the RELATED-TO
property with a RELTYPE=SERIES-MASTER parameter.
The full series of components can only be retrieved by searching
for all components with a matching RELATED-TO property.
If the value of the "DTSTART" property is a DATE type value, then
the value MUST be the calendar date for the series instance.
The DATE-TIME value is set to the time when the original series
instance would occur; meaning that if the intent is to change a
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Friday meeting to Thursday, the DATE-TIME is still set to the
original Friday meeting.
The "SERIES-ID" property is used in conjunction with the "UID" and
"SEQUENCE" properties to identify a particular instance of an
event, to-do, or journal in the series. For a given pair of "UID"
and "SEQUENCE" property values, the "SERIES-ID" value for a series
instance is fixed.
Format Definition:
This property is defined by the following notation:
serid = "SERIES-ID" sidparam ":" sidval CRLF
sidparam = *(
;
; The following are OPTIONAL,
; but MUST NOT occur more than once.
;
(";" "VALUE" "=" ("DATE-TIME" / "DATE")) /
(";" tzidparam) /
;
; The following is OPTIONAL,
; and MAY occur more than once.
;
(";" other-param)
;
)
sidval = date-time / date
;Value MUST match value type
Example:
The following are examples of this property:
SERIES-ID;VALUE=DATE:19960401
SERIES-ID;TZID=America/New_York:20170120T120000
6.6. Last series id
Property name: LAST-SERIES-ID
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Purpose: To specify the last calculated instance of the series.
When new instances are created they MUST have a SERIES-ID after
the value of this property.
In all respects this property is identical to SERIES-ID and is in
fact a copy of the SERIES-ID which would be present in the last
created instance (assuming it is not suppressed by an SXDATE).
Value type: DATE or DATE_TIME (the default). This has the same
requirements as SERIES-ID.
Property Parameters: IANA, non-standard, value data type and time
zone identifier parameters can be specified on this property.
Conformance: This property MAY be specified in any iCalendar
component.
Description: When used in a component the value of this property
points to additional information related to the component. For
example, it may reference the originating web server.
Format Definition:
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This property is defined by the following notation:
last-series-i = "LAST-SERIES-ID" lastseriesidparam /
(
";" "VALUE" "=" "TEXT"
":" text
)
(
";" "VALUE" "=" "REFERENCE"
":" text
)
(
";" "VALUE" "=" "URI"
":" uri
)
CRLF
lastseriesidparam = *(
; the following is MANDATORY
; and MAY occur more than once
(";" relparam) /
; the following are MANDATORY
; but MUST NOT occur more than once
(";" fmttypeparam) /
(";" labelparam) /
; labelparam is defined in ...
; the following is OPTIONAL
; and MAY occur more than once
(";" xparam)
)
Example:
The following is an example of this property. It points to a server
acting as the source for the calendar object.
LINK;REL=SOURCE;LABEL=The Egg:http://example.com/events
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6.7. Series Rule
Property name: RRULE
Purpose: This property defines a rule or repeating pattern for a
series of events, to-dos or journal entries.
Value Type: RECUR
Property Parameters: IANA, non-standard, look-ahead count or date
property parameters can be specified on this property.
Conformance: This property can be specified in any "VEVENT",
"VTODO", and "VJOURNAL" calendar component, but it SHOULD NOT be
specified more than once.
Description: The series rule, if specified, is used in computing the
instances to be generated for the series. These are generated by
considering the master "DTSTART" property along with the "SRULE",
"SDATE", and "SXDATE" properties contained within the series
master. The "DTSTART" property defines the first instance in the
recurrence set which is represented by that master event.
Unlike the RRULE the "DTSTART" property MUST be synchronized with
the series rule, if specified. For example, if the DTSTARTS
species a date on Wednesday but the SRULE speciee every Tuesday
then a server or client MUSt reject the component.
The final series is represented by gathering all of the start
DATE-TIME values generated by any of the specified "SRULE" and
"SDATE" properties, and then excluding any start DATE-TIME values
specified by "SXDATE" properties. This implies that start DATE-
TIME values specified by "SXDATE" properties take precedence over
those specified by inclusion properties (i.e., "SDATE" and
"SRULE"). Where duplicate instances are generated by the "SRULE"
and "SDATE" properties, only one imstance is considered.
Duplicate instances are ignored.
The "DTSTART" property specified within the master iCalendar
object defines the first instance of the recurrence. In most
cases, a "DTSTART" property of DATE-TIME value type used with a
series rule, should be specified as a date with local time and
time zone reference to make sure all the recurrence instances
start at the same local time regardless of time zone changes.
If the duration of the series component is specified with the
"DTEND" or "DUE" property, then the same exact duration will apply
to all the members of the generated series. Else, if the duration
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of the series master component is specified with the "DURATION"
property, then the same nominal duration will apply to all the
members of the generated series and the exact duration of each
instance will depend on its specific start time. For example,
series instances of a nominal duration of one day will have an
exact duration of more or less than 24 hours on a day where a time
zone shift occurs. The duration of a specific instance may be
modified in an exception component or simply by using an "SDATE"
property of PERIOD value type.
Format Definition:
This property is defined by the following notation:
srule = "SRULE" srulparam ":" recur CRLF
sruleparam = *(
; the following are OPTIONAL
; but MUST NOT occur more than once
(";" lookahead-countparam) /
(";" lookahead-periodparam) /
; the following is OPTIONAL
; and MAY occur more than once
(";" xparam)
)
Examples: Say they are pretty much the same as RRULE but extra
params
7. Redefined RELATED-TO Property
7.1. RELATED-TO
Property name: RELATED-TO
Purpose: This property is used to represent a relationship or
reference between one calendar component and others. The
definition here extends the definition in Section 3.8.4.5. of
[RFC5545] by including a section on RELTYPE=SERIES-MASTER.
Value type: URI, UID or TEXT
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Property Parameters: Relationship type, IANA and non-standard
property parameters can be specified on this property.
Conformance: This property MAY be specified in any iCalendar
component.
Description: By default or when VALUE=UID is specified, the property
value consists of the persistent, globally unique identifier of
another calendar component. This value would be represented in a
calendar component by the "UID" property.
By default, the property value points to another calendar
component that has a PARENT relationship to the referencing
object. The "RELTYPE" property parameter is used to either
explicitly state the default PARENT relationship type to the
referenced calendar component or to override the default PARENT
relationship type and specify either a CHILD or SIBLING
relationship or a temporal relationship.
The PARENT relationship indicates that the calendar component is a
subordinate of the referenced calendar component. The CHILD
relationship indicates that the calendar component is a superior
of the referenced calendar component. The SIBLING relationship
indicates that the calendar component is a peer of the referenced
calendar component.
The FINISHTOSTART, FINISHTOFINISH, STARTTOFINISH or STARTTOSTART
relationships define temporal relationships as specified in the
reltype parameter definition.
The SERIES-MASTER relationship when included in a series instance
refers to the master of that series. When included in a series
master it refers to a previous master in a chain of spilt series.
Changes to a calendar component referenced by this property can
have an implicit impact on the related calendar component. For
example, if a group event changes its start or end date or time,
then the related, dependent events will need to have their start
and end dates changed in a corresponding way. Similarly, if a
PARENT calendar component is cancelled or deleted, then there is
an implied impact to the related CHILD calendar components. This
property is intended only to provide information on the
relationship of calendar components. It is up to the target
calendar system to maintain any property implications of this
relationship.
Format Definition:
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This property is defined by the following notation:
related = "RELATED-TO" relparam ( ":" text ) /
(
";" "VALUE" "=" "UID"
":" uid
)
(
";" "VALUE" "=" "URI"
":" uri
)
CRLF
relparam = *(
;
; The following are OPTIONAL,
; but MUST NOT occur more than once.
;
(";" reltypeparam) /
(";" gapparam) /
;
; The following is OPTIONAL,
; and MAY occur more than once.
;
(";" other-param)
;
)
Example:
The following are examples of this property.
RELATED-TO;RELTYPE=SERIES-MASTER:19960401-080045-4000F192713
8. Backwards compatibility
Any clients following the approach specified in [RFC5545] are
expected to ignore any properties or parameters they don't recognize.
For such clients the series appears to be an unconnected set of
components. They all have their own unique UIDS. If the client
updates an instance this should be identical in effect to an update
carried out by a client aware of the new properties.
Updates MUST preserve the SERIES-ID, LAST-SERIES-ID, SRULE, SDATE and
SXDATE properties. A client which does not do so is in violation of
[RFC5545].
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More text needed here...
9. CalDAV extensions
This specification may extend Caldav by adding reports to return all
members of a series given the series master UID. This could be
handled by the current query mechganism but it is likely to be
sufficiently frequently used that a special query is appropriate.
It is also likely we will want a CalDAV operation to split a series
and generate the additional members of the series as a single atomic
operation.
10. Security Considerations
Clients and servers should take care to limit the number of generated
instances to a reasonable value. This can be a relatively small
value.
11. IANA Considerations
11.1. iCalendar Property Registrations
The following iCalendar property names have been added to the
iCalendar Properties Registry defined in Section 8.3.2 of [RFC5545]
+----------------+---------+-------------+
| Property | Status | Reference |
+----------------+---------+-------------+
| LAST-SERIES-ID | Current | Section 6.6 |
| SERIES-ID | Current | Section 6.5 |
| SERIES-UID | Current | Section 6.2 |
| SDATE | Current | Section 6.4 |
| SRULE | Current | Section 6.7 |
| SXDATE | Current | Section 6.3 |
+----------------+---------+-------------+
11.2. iCalendar Property Parameter Registrations
The following iCalendar property parameter names have been added to
the iCalendar Parameters Registry defined in Section 8.3.3 of
[RFC5545]
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+------------------+---------+-------------+
| Parameter | Status | Reference |
+------------------+---------+-------------+
| LOOKAHEAD-COUNT | Current | Section 5.2 |
| LOOKAHEAD-PERIOD | Current | Section 5.3 |
| SPLIT | Current | Section 5.1 |
+------------------+---------+-------------+
11.3. iCalendar RELTYPE Value Registrations
The following iCalendar "RELTYPE" values have been added to the
iCalendar Relationship Types Registry defined in Section 8.3.8 of
[RFC5545]
+-------------------+---------+-----------+
| Relationship Type | Status | Reference |
+-------------------+---------+-----------+
| SERIES-ID | Current | Section 4 |
+-------------------+---------+-----------+
12. Acknowledgements
The author would like to thank the members of the Calendaring and
Scheduling Consortium technical committees and the following
individuals for contributing their ideas, support and comments:
The author would also like to thank the Calendaring and Scheduling
Consortium for advice with this specification.
13. Normative References
[I-D.daboo-caldav-attachments]
Daboo, C. and A. Quillaud, "CalDAV Managed Attachments",
draft-daboo-caldav-attachments-03 (work in progress),
February 2014.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://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,
<http://www.rfc-editor.org/info/rfc3986>.
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[RFC5545] Desruisseaux, B., Ed., "Internet Calendaring and
Scheduling Core Object Specification (iCalendar)",
RFC 5545, DOI 10.17487/RFC5545, September 2009,
<http://www.rfc-editor.org/info/rfc5545>.
[RFC5988] Nottingham, M., "Web Linking", RFC 5988,
DOI 10.17487/RFC5988, October 2010,
<http://www.rfc-editor.org/info/rfc5988>.
[RFC7986] Daboo, C., "New Properties for iCalendar", RFC 7986,
DOI 10.17487/RFC7986, October 2016,
<http://www.rfc-editor.org/info/rfc7986>.
[W3C.REC-xml-20060816]
Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E., and
F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fourth
Edition)", World Wide Web Consortium Recommendation REC-
xml-20060816, August 2006,
<http://www.w3.org/TR/2006/REC-xml-20060816>.
[W3C.WD-xptr-xpointer-20021219]
DeRose, S., Daniel, R., and E. Maler, "XPointer xpointer()
Scheme", World Wide Web Consortium WD WD-xptr-xpointer-
20021219, December 2002,
<http://www.w3.org/TR/2002/WD-xptr-xpointer-20021219>.
Appendix A. Points for discussion
Detecting changes from old clients: If such a client updates
properties in the master ... what do we say here? Is there a way
we can determine that the client doesn't realize that it's a
series? If it doesn't then updating the dtstart is a big deal -
maybe we add a parameter to a dtstart update to indicate the
client knows it's a series but wants to do so anyway.
Or perhaps we add a new operation - or extend patch. Simple
update returns FORBIDDEN if you try to change any of the important
properties (should do that for recurrences) and requires an
explicit flag to say you (think you) know what you're doing.
Splitting and linking: The spec currently only allows for backward
linking to previous masters. There is a parameter added to the
rule SPLIT=YES to indicate that the series was split
It makes sense to have a forward link to the new(er) series.
However, a client/server may not know what the UID is until after
data is stored. The new chain can be determined vis a query so
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perhaps we can leave it up to the protocols to figure out that
mechanism.
CalDAV queries: if there were a better more generalised query
language such an extensions might be unnecessary. Should we
define a query language specifically for calendaring?
Appendix B. Change log
2017-02-12 MD Initial version
Author's Address
Michael Douglass
Spherical Cow Group
226 3rd Street
Troy, NY 12180
USA
Email: mdouglass@sphericalcowgroup.com
URI: http://sphericalcowgroup.com
Douglass Expires August 19, 2017 [Page 26]
