Internet Engineering Task Force (IETF) C. Daboo
Request for Comments: 6321 Apple, Inc.
Category: Standards Track M. Douglass
ISSN: 2070-1721 RPI
S. Lees
Microsoft
August 2011
xCal: The XML Format for iCalendar
Abstract
This specification defines "xCal", an XML format for iCalendar data.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6321.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction ....................................................3
2. Conventions Used in This Document ...............................4
3. Converting from iCalendar to xCal ...............................4
3.1. Pre-Processing .............................................4
3.2. iCalendar Stream (RFC 5545, Section 3.4) ...................5
3.3. Components (RFC 5545, Section 3.6) .........................6
3.4. Properties (RFC 5545, Sections 3.7 and 3.8) ................6
3.4.1. Special Cases for Properties ........................8
3.4.1.1. Multi-Valued Properties ....................8
3.4.1.2. GEO Property ...............................9
3.4.1.3. REQUEST-STATUS Property ....................9
3.5. Parameters (RFC 5545, Section 3.2) ........................10
3.5.1. VALUE Parameter ....................................11
3.6. Values (RFC 5545, Section 3.3) ............................11
3.6.1. Binary (RFC 5545, Section 3.3.1) ...................12
3.6.2. Boolean (RFC 5545, Section 3.3.2) .................12
3.6.3. Calendar User Address (RFC 5545, Section 3.3.3) ....12
3.6.4. Date (RFC 5545, Section 3.3.4) .....................12
3.6.5. Date-Time (RFC 5545, Section 3.3.5) ................13
3.6.6. Duration (RFC 5545, Section 3.3.6) .................13
3.6.7. Float (RFC 5545, Section 3.3.7) ....................13
3.6.8. Integer (RFC 5545, Section 3.3.8) ..................14
3.6.9. Period of Time (RFC 5545, Section 3.3.9) ...........14
3.6.10. Recurrence Rule (RFC 5545, Section 3.3.10) ........14
3.6.11. Text (RFC 5545, Section 3.3.11) ...................15
3.6.12. Time (RFC 5545, Section 3.3.12) ...................15
3.6.13. URI (RFC 5545, Section 3.3.13) ....................15
3.6.14. UTC Offset (RFC 5545, Section 3.3.14) .............16
3.7. Extensions ................................................16
4. Converting from xCal into iCalendar ............................16
4.1. Converting XML Extensions into iCalendar ..................16
4.2. The XML Property for iCalendar ............................17
5. Handling Unrecognized Properties or Parameters .................18
6. Security Considerations ........................................19
7. IANA Considerations ............................................20
7.1. Namespace Registration ....................................20
7.2. Media Type ................................................20
7.3. iCalendar Property Registrations ..........................21
8. Acknowledgments ................................................22
9. References .....................................................22
9.1. Normative References ......................................22
9.2. Informative References ....................................22
Appendix A. RELAX NG Schema .......................................23
Appendix B. Examples ..............................................49
B.1. Example 1 ..................................................49
B.1.1. iCalendar Data .........................................49
B.1.2. XML Data ...............................................49
B.2. Example 2 ..................................................50
B.2.1. iCalendar Data .........................................50
B.2.2. XML Data ...............................................51
1. Introduction
The iCalendar data format [RFC5545] is a widely deployed interchange
format for calendaring and scheduling data. While many applications
and services consume and generate calendar data, iCalendar is a
specialized format that requires its own parser/generator. In
contrast, XML-based formats are widely used for interoperability
between applications, and the many tools that generate, parse, and
manipulate XML make it easier to work with than iCalendar.
The purpose of this specification is to define "xCal", an XML format
for iCalendar data. xCal is defined as a straightforward mapping into
XML from iCalendar, so that iCalendar data can be converted to XML,
and then back to iCalendar, without losing any semantic meaning in
the data. Anyone creating xCal calendar data according to this
specification will know that their data can be converted to a valid
iCalendar representation as well.
Key design considerations are:
Round-tripping (converting an iCalendar instance to xCal and back)
will give the same semantic result as the starting point. That
is, all components, properties, and property parameters are
guaranteed to be preserved, with the exception of those that have
default values.
xCal preserves the semantics of the iCalendar data. While a
simple consumer can easily browse the calendar data in xCal, a
full understanding of iCalendar is still required in order to
modify and/or fully comprehend the calendar data.
xCal has the ability to handle many extensions to the underlying
iCalendar specification without requiring an update to this
document.
2. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
When XML element types in the namespace
"urn:ietf:params:xml:ns:icalendar-2.0" are referenced in this
document outside of the context of an XML fragment, the string "IC:"
will be prefixed to the element types.
Some examples in this document contain "partial" XML documents used
for illustrative purposes. In these examples, three periods "..."
are used to indicate a portion of the document that has been removed
for compactness.
3. Converting from iCalendar to xCal
This section describes how iCalendar data is converted to xCal using
a simple mapping between the iCalendar data model and XML elements.
3.1. Pre-Processing
iCalendar uses a line folding mechanism to limit lines of data to a
maximum line length (typically 72 characters) to ensure maximum
likelihood of preserving data integrity as it is transported via
various means (e.g., email) -- see Section 3.1 of [RFC5545]. Prior
to converting iCalendar data into xCal, all folded lines MUST be
unfolded.
iCalendar data uses an "escape" character sequence for text values
and property parameter values. When such text elements are converted
into xCal, the escaping MUST be removed.
iCalendar uses a base64 encoding for binary data. However, it does
not restrict the encoding from being applied to non-binary value
types. So, the following rules MUST be applied when processing a
property with the "ENCODING" property parameter set to "BASE64":
o If the property value type is "BINARY", the base64 encoding MUST
be preserved.
o If the value type is not "BINARY", the "ENCODING" property
parameter MUST be removed, and the value MUST be base64 decoded.
When base64 encoding and decoding are used, they MUST conform to
Section 4 of [RFC4648], which is the base64 method used in [RFC5545].
One key difference in the formatting of values used in iCalendar and
xCal is that, in xCal, the specification uses date/time and UTC
offset values aligned with the syntax of
[W3C.REC-xmlschema-2-20041028] to aid with XML processing.
3.2. iCalendar Stream (RFC 5545, Section 3.4)
At the top level of the iCalendar object model is an "iCalendar
stream". This object encompasses multiple "iCalendar objects". In
xCal, the entire stream is contained in the root IC:icalendar XML
element.
An iCalendar stream can contain one or more iCalendar objects. Each
iCalendar object, delimited by "BEGIN:VCALENDAR" and "END:VCALENDAR",
is enclosed by the IC:vcalendar XML element.
Example:
<?xml version="1.0" encoding="utf-8"?>
<icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
<vcalendar>
...
</vcalendar>
</icalendar>
iCalendar objects are comprised of a set of "components",
"properties", "parameters", and "values". A "component" can contain
other "components" or "properties". A "property" has a value and a
set of zero or more "parameters".
In xCal, component elements, for example, IC:vevent and IC:vtodo, are
contained within an IC:components XML element. Within the component
element, another IC:components element could appear (representing
components nested within components) or the IC:properties XML element
could appear. IC:properties is used to encapsulate iCalendar
properties.
Each iCalendar property will be mapped to its own XML element as
described below. Within each of these elements, there is zero or one
IC:parameters XML element used to encapsulate any iCalendar property
parameters. Additionally there will be one or more XML elements
representing the value of the iCalendar property.
Example:
<?xml version="1.0" encoding="utf-8"?>
<icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
<vcalendar>
<properties>
...
</properties>
<components>
...
</components>
</vcalendar>
</icalendar>
+------------------+--------------+------------------+
| Item | XML element | XML Definition |
+------------------+--------------+------------------+
| iCalendar Stream | IC:icalendar | Appendix A # 3.4 |
| VCALENDAR | IC:vcalendar | Appendix A # 3.6 |
+------------------+--------------+------------------+
3.3. Components (RFC 5545, Section 3.6)
Each calendar component in the "VCALENDAR" object, delimited by
"BEGIN" and "END", will be converted to an enclosing XML element with
the same name, but in lowercase. As an example, the table below
shows iCalendar-to-xCal mappings for current iCalendar components.
Any new iCalendar components added in the future will be converted in
the same way.
+-----------+--------------+--------------------+
| Component | XML element | XML Definition |
+-----------+--------------+--------------------+
| VEVENT | IC:vevent | Appendix A # 3.6.1 |
| VTODO | IC:vtodo | Appendix A # 3.6.2 |
| VJOURNAL | IC:vjournal | Appendix A # 3.6.3 |
| VFREEBUSY | IC:vfreebusy | Appendix A # 3.6.4 |
| VTIMEZONE | IC:vtimezone | Appendix A # 3.6.5 |
| STANDARD | IC:standard | Appendix A # 3.6.5 |
| DAYLIGHT | IC:daylight | Appendix A # 3.6.5 |
| VALARM | IC:valarm | Appendix A # 3.6.6 |
+-----------+--------------+--------------------+
3.4. Properties (RFC 5545, Sections 3.7 and 3.8)
iCalendar properties, whether they apply to the "VCALENDAR" object or
to a component, are handled in a consistent way in the xCal format.
iCalendar properties are enclosed in the XML element IC:properties.
Each individual iCalendar property is represented in xCal by an
element of the same name as the iCalendar property, but in lowercase.
For example, the "CALSCALE" property is represented in xCal by the
IC:calscale element.
Example:
<?xml version="1.0" encoding="utf-8"?>
<icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
<vcalendar>
<properties>
<calscale>...</calscale>
<version>...</version>
<prodid>...</prodid>
</properties>
<components>
...
</components>
</vcalendar>
</icalendar>
Each property can contain an IC:parameters XML element encapsulating
any iCalendar property parameters associated with the iCalendar
property.
Each property will contain one or more "value" XML elements as
described below representing the value of the iCalendar property.
As an example, the table below shows iCalendar-to-xCal mappings for
current iCalendar properties. Any new iCalendar properties added in
the future will be converted in the same way.
+------------------+---------------------+-----------------------+
| Property | XML element | XML Definition |
+------------------+---------------------+-----------------------+
| CALSCALE | IC:calscale | Appendix A # 3.7.1 |
| METHOD | IC:method | Appendix A # 3.7.2 |
| PRODID | IC:prodid | Appendix A # 3.7.3 |
| VERSION | IC:version | Appendix A # 3.7.4 |
| ATTACH | IC:attach | Appendix A # 3.8.1.1 |
| CATEGORIES | IC:categories | Appendix A # 3.8.1.2 |
| CLASS | IC:class | Appendix A # 3.8.1.3 |
| COMMENT | IC:comment | Appendix A # 3.8.1.4 |
| DESCRIPTION | IC:description | Appendix A # 3.8.1.5 |
| GEO | IC:geo | Appendix A # 3.8.1.6 |
| LOCATION | IC:location | Appendix A # 3.8.1.7 |
| PERCENT-COMPLETE | IC:percent-complete | Appendix A # 3.8.1.8 |
| PRIORITY | IC:priority | Appendix A # 3.8.1.9 |
| RESOURCES | IC:resources | Appendix A # 3.8.1.10 |
| STATUS | IC:status | Appendix A # 3.8.1.11 |
| SUMMARY | IC:summary | Appendix A # 3.8.1.12 |
| COMPLETED | IC:completed | Appendix A # 3.8.2.1 |
| DTEND | IC:dtend | Appendix A # 3.8.2.2 |
| DUE | IC:due | Appendix A # 3.8.2.3 |
| DTSTART | IC:dtstart | Appendix A # 3.8.2.4 |
| DURATION | IC:duration | Appendix A # 3.8.2.5 |
| FREEBUSY | IC:freebusy | Appendix A # 3.8.2.6 |
| TRANSP | IC:transp | Appendix A # 3.8.2.7 |
| TZID | IC:tzid | Appendix A # 3.8.3.1 |
| TZNAME | IC:tzname | Appendix A # 3.8.3.2 |
| TZOFFSETFROM | IC:tzoffsetfrom | Appendix A # 3.8.3.3 |
| TZOFFSETTO | IC:tzoffsetto | Appendix A # 3.8.3.4 |
| TZURL | IC:tzurl | Appendix A # 3.8.3.5 |
| ATTENDEE | IC:attendee | Appendix A # 3.8.4.1 |
| CONTACT | IC:contact | Appendix A # 3.8.4.2 |
| ORGANIZER | IC:organizer | Appendix A # 3.8.4.3 |
| RECURRENCE-ID | IC:recurrence-id | Appendix A # 3.8.4.4 |
| RELATED-TO | IC:related-to | Appendix A # 3.8.4.5 |
| URL | IC:url | Appendix A # 3.8.4.6 |
| UID | IC:uid | Appendix A # 3.8.4.7 |
| EXDATE | IC:exdate | Appendix A # 3.8.5.1 |
| RDATE | IC:rdate | Appendix A # 3.8.5.2 |
| RRULE | IC:rrule | Appendix A # 3.8.5.3 |
| ACTION | IC:action | Appendix A # 3.8.6.1 |
| REPEAT | IC:repeat | Appendix A # 3.8.6.2 |
| TRIGGER | IC:trigger | Appendix A # 3.8.6.3 |
| CREATED | IC:created | Appendix A # 3.8.7.1 |
| DTSTAMP | IC:dtstamp | Appendix A # 3.8.7.2 |
| LAST-MODIFIED | IC:last-modified | Appendix A # 3.8.7.3 |
| SEQUENCE | IC:sequence | Appendix A # 3.8.7.4 |
| REQUEST-STATUS | IC:request-status | Appendix A # 3.8.8.3 |
+------------------+---------------------+-----------------------+
3.4.1. Special Cases for Properties
This section describes some properties that have special handling
when converting to xCal.
3.4.1.1. Multi-Valued Properties
The following iCalendar properties can have values that consist of a
list of "standard" iCalendar values separated by a specific
delimiter. In xCal, these properties are represented by an XML
element that contains multiple "value" elements (Section 3.6).
+------------+---------------+-----------------------+
| Property | XML element | XML Definition |
+------------+---------------+-----------------------+
| CATEGORIES | IC:categories | Appendix A # 3.8.1.2 |
| RESOURCES | IC:resources | Appendix A # 3.8.1.10 |
| FREEBUSY | IC:freebusy | Appendix A # 3.8.2.6 |
| EXDATE | IC:exdate | Appendix A # 3.8.5.1 |
| RDATE | IC:rdate | Appendix A # 3.8.5.2 |
+------------+---------------+-----------------------+
3.4.1.2. GEO Property
In iCalendar, the "GEO" property value is defined as a semicolon-
separated list of two "FLOAT" values; the first representing latitude
and the second longitude.
In xCal, the value for the IC:geo element is represented by two XML
elements. These are an IC:latitude element and an IC:longitude
element, each of which contains float values. See Appendix A #
3.8.1.6.
Example:
<?xml version="1.0" encoding="utf-8"?>
<icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
...
<geo>
<latitude>37.386013</latitude>
<longitude>-122.082932</longitude>
</geo>
...
</icalendar>
3.4.1.3. REQUEST-STATUS Property
In iCalendar, the "REQUEST-STATUS" property value is defined as a
semicolon-separated list of two or three "TEXT" values. The first
represents a code, the second a description, and the third any
additional data.
In xCal, the value for the IC:request-status element is represented
by two or three XML elements. These are an IC:code element, an IC:
description element, and an IC:data element, each of which contains
the corresponding "TEXT" values. If there is no additional data in
the iCalendar value, the IC:data element (which would be empty)
SHOULD NOT be present. See Appendix A # 3.8.8.3.
Example:
<?xml version="1.0" encoding="utf-8"?>
<icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
...
<request-status>
<code>2.0</code>
<description>Success</description>
</request-status>
...
</icalendar>
3.5. Parameters (RFC 5545, Section 3.2)
iCalendar property parameters are enclosed in the XML element IC:
parameters, which occurs in each property XML element. If there are
no iCalendar property parameters, the IC:parameters element (which
would be empty) SHOULD NOT be present.
Each individual iCalendar property parameter is represented in xCal
by an element of the same name as the iCalendar property parameter,
but in lowercase. For example, the "PARTSTAT" property parameter is
represented in xCal by the IC:partstat element.
Example:
<?xml version="1.0" encoding="utf-8"?>
<icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
<vcalendar>
...
<components>
...
<attendee>
<parameters>
<partstat><text>NEEDS-ACTION</text></partstat>
</parameters>
...
</attendee>
...
</components>
</vcalendar>
</icalendar>
Each XML parameter element contains one or more child XML elements
representing iCalendar value types.
As an example, the table below shows iCalendar-to-xCal mappings for
current iCalendar parameters. Any new iCalendar parameters added in
the future will be converted in the same way.
+----------------+-------------------+---------------------+
| Parameter | XML element | XML Definition |
+----------------+-------------------+---------------------+
| ALTREP | IC:altrep | Appendix A # 3.2.1 |
| CN | IC:cn | Appendix A # 3.2.2 |
| CUTYPE | IC:cutype | Appendix A # 3.2.3 |
| DELEGATED-FROM | IC:delegated-from | Appendix A # 3.2.4 |
| DELEGATED-TO | IC:delegated-to | Appendix A # 3.2.5 |
| DIR | IC:dir | Appendix A # 3.2.6 |
| ENCODING | IC:encoding | Appendix A # 3.2.7 |
| FMTTYPE | IC:fmttype | Appendix A # 3.2.8 |
| FBTYPE | IC:fbtype | Appendix A # 3.2.9 |
| LANGUAGE | IC:language | Appendix A # 3.2.10 |
| MEMBER | IC:member | Appendix A # 3.2.11 |
| PARTSTAT | IC:partstat | Appendix A # 3.2.12 |
| RANGE | IC:range | Appendix A # 3.2.13 |
| RELATED | IC:related | Appendix A # 3.2.14 |
| RELTYPE | IC:reltype | Appendix A # 3.2.15 |
| ROLE | IC:role | Appendix A # 3.2.16 |
| RSVP | IC:rsvp | Appendix A # 3.2.17 |
| SENT-BY | IC:sent-by | Appendix A # 3.2.18 |
| TZID | IC:tzid | Appendix A # 3.2.19 |
+----------------+-------------------+---------------------+
3.5.1. VALUE Parameter
iCalendar defines a "VALUE" property parameter (Section 3.2.20 of
[RFC5545]). This property parameter is not mapped to an xCal XML
element. Instead, the value type is handled by having different XML
elements for each value, and these appear inside of property
elements. Thus, when converting from iCalendar to xCal, any "VALUE"
property parameters are skipped. When converting from xCal into
iCalendar, the appropriate "VALUE" property parameter MUST be
included in the iCalendar property if the value type is not the
default value type for that property.
3.6. Values (RFC 5545, Section 3.3)
In the typical case, iCalendar value types are mapped into XML
elements with a matching name in all lowercase. In the case of the
value for a recurrence rule (see below), iCalendar defines
"structured" values, and these are mapped into separate child
elements for each value element.
3.6.1. Binary (RFC 5545, Section 3.3.1)
Description: iCalendar "BINARY" property values are represented by
the IC:binary XML element. The content of the element is base64
encoded data, conforming to Section 4 of [RFC4648], which is the
base64 method used in [RFC5545]. Whitespace MAY be inserted into
the data at any point to "wrap" the data to reasonable line
lengths. When converting back to iCalendar, the whitespace MUST
first be removed.
XML Definition: Appendix A # 3.3.1
Example:
<binary>SGVsbG8gV29ybGQh</binary>
3.6.2. Boolean (RFC 5545, Section 3.3.2)
Description: iCalendar "BOOLEAN" property values are represented by
the IC:boolean XML element. The content of the element is a
boolean value.
XML Definition: Appendix A # 3.3.2
Example:
<boolean>true</boolean>
3.6.3. Calendar User Address (RFC 5545, Section 3.3.3)
Description: iCalendar "CAL-ADDRESS" property values are represented
by the IC:cal-address XML element. The content of the element is
a URI.
XML Definition: Appendix A # 3.3.3
Example:
<cal-address>mailto:cyrus@example.com</cal-address>
3.6.4. Date (RFC 5545, Section 3.3.4)
Description: iCalendar "DATE" property values are represented by the
IC:date XML element. The content of the element is the same date
value specified by [RFC5545], with the exception that the date
components are separated by "-" characters, for consistency with
[W3C.REC-xmlschema-2-20041028].
XML Definition: Appendix A # 3.3.4
Example:
<date>2011-05-17</date>
3.6.5. Date-Time (RFC 5545, Section 3.3.5)
Description: iCalendar "DATE-TIME" property values are represented
by the IC:date-time XML element. The content of the element is
the same date-time value specified by [RFC5545], with the
exception that the date components are separated by "-"
characters, and the time components are separated by ":"
characters, for consistency with [W3C.REC-xmlschema-2-20041028].
Note that while [W3C.REC-xmlschema-2-20041028] allows for a UTC
offset to be included in date/time values, xCal does not use that,
and instead follows the iCalendar behavior of using time zone
definitions via the "TZID" property parameter.
XML Definition: Appendix A # 3.3.5
Example:
<date-time>2011-05-17T12:00:00</date-time>
3.6.6. Duration (RFC 5545, Section 3.3.6)
Description: iCalendar "DURATION" property values are represented by
the IC:duration XML element. The content of the element is the
same duration value specified by [RFC5545].
XML Definition: Appendix A # 3.3.6
Example:
<duration>P1D</duration>
3.6.7. Float (RFC 5545, Section 3.3.7)
Description: iCalendar "FLOAT" property values are represented by
the IC:float XML element. The content of the element is a text
representation of a floating point number.
XML Definition: Appendix A # 3.3.7
Example:
<float>0.5</float>
3.6.8. Integer (RFC 5545, Section 3.3.8)
Description: iCalendar "INTEGER" property values are represented by
the IC:integer XML element. The content of the element is a text
representation of an integer number.
XML Definition: Appendix A # 3.3.8
Examples:
<integer>50</integer>
<integer>-100</integer>
3.6.9. Period of Time (RFC 5545, Section 3.3.9)
Description: iCalendar "PERIOD" property values are represented by
the IC:period XML element. The content of the element is child
elements representing the start, end, or duration components of
the period.
XML Definition: Appendix A # 3.3.9
Example:
<period>
<start>2011-05-17T12:00:00</start>
<duration>P1H</duration>
</period>
3.6.10. Recurrence Rule (RFC 5545, Section 3.3.10)
Description: iCalendar "RECUR" property values are represented by
the IC:recur XML element. The content of the element is child
elements representing the various components of a recurrence rule.
XML Definition: Appendix A # 3.3.10
Example:
<recur>
<freq>YEARLY</freq>
<count>5</count>
<byday>-1SU</byday>
<bymonth>10</bymonth>
</recur>
3.6.11. Text (RFC 5545, Section 3.3.11)
Description: iCalendar "TEXT" property values are represented by the
IC:text XML element. The content of the element is simple text.
XML Definition: Appendix A # 3.3.11
Example:
<text>Hello World!</text>
3.6.12. Time (RFC 5545, Section 3.3.12)
Description: iCalendar "TIME" property values are represented by the
IC:time XML element. The content of the element is the same time
value specified by [RFC5545], with the exception that the time
components are separated by ":" characters, for consistency with
[W3C.REC-xmlschema-2-20041028]. Note that while
[W3C.REC-xmlschema-2-20041028] allows for a UTC offset to be
included in date/time values, xCal does not use that, and instead
follows the iCalendar behavior of using time zone definitions via
the "TZID" property parameter.
XML Definition: Appendix A # 3.3.12
Example:
<time>12:00:00</time>
3.6.13. URI (RFC 5545, Section 3.3.13)
Description: iCalendar "URI" property values are represented by the
IC:uri XML element. The content of the element is a URI.
XML Definition: Appendix A # 3.3.13
Example:
<uri>http://calendar.example.com</uri>
3.6.14. UTC Offset (RFC 5545, Section 3.3.14)
Description: iCalendar "UTC-OFFSET" property values are represented
by the IC:utc-offset XML element. The content of the element is
the same UTC offset value specified by [RFC5545], with the
exception that the hour, minute, and second components are
separated by a ":" character, for consistency with
[W3C.REC-xmlschema-2-20041028].
XML Definition: Appendix A # 3.3.14
Example:
<utc-offset>-05:00</utc-offset>
3.7. Extensions
iCalendar extension properties and property parameters (those with an
"X-" prefix in their name) are handled in the same way as other
properties and property parameters: the property or property
parameter is represented by an XML element with the same name, but in
lowercase, e.g., the "X-FOO" property in iCalendar turns into the IC:
x-foo element in xCal. However, see Section 5 for how to deal with
default values for unrecognized extension properties or property
parameters.
4. Converting from xCal into iCalendar
When converting component, property, and property parameter values,
the names SHOULD be converted to uppercase. Although iCalendar names
are case insensitive, common practice is to keep them all uppercase
following the actual definitions in [RFC5545].
BACKSLASH character encoding and line folding MUST be applied to the
resulting iCalendar data as required by [RFC5545].
Non-binary value types MUST NOT be base64 encoded.
4.1. Converting XML Extensions into iCalendar
XML extensions are converted back to iCalendar in one of two ways,
depending on whether the extensions are in the iCalendar XML
namespace or in an external namespace.
Extensions that are part of the iCalendar XML namespace MUST have
element names that begin with "x-", and will be converted back to the
equivalent extension property in iCalendar. For example, the "x-foo"
element will convert to the "X-FOO" iCalendar property.
Extensions that are in a namespace other than the iCalendar XML
namespace SHOULD be preserved in the iCalendar representation using
the "XML" iCalendar property described in Section 4.2. Only those
extension elements that are immediate child elements of the IC:
properties element are converted, any others are ignored.
4.2. The XML Property for iCalendar
This section describes an extension property for iCalendar, as
covered in Section 8.2.3 of [RFC5545].
Property name: XML
Purpose: To embed extended XML-encoded iCalendar data in the
iCalendar format.
Value type: The default value type is "TEXT". The value type can
also be set to "BINARY" to indicate base64 encoded content.
Property parameters: IANA, non-standard, inline encoding, and value
data type property parameters can be specified on this property.
Conformance: The property can be specified multiple times in any
calendar component.
Description: The value of this property is a single XML 1.0
[W3C.REC-xml-20081126] element. The "XML" property MUST NOT be used
to contain properties that are already defined in iCalendar. Since
all elements in the urn:ietf:params:xml:ns:icalendar-2.0 namespace
convert to a well-defined iCalendar object, the elements in this
property MUST NOT be in the urn:ietf:params:xml:ns:icalendar-2.0
namespace. The XML element that is the value of this property MUST
have an XML namespace declaration.
The default value type for this property is "TEXT", and normal
BACKSLASH character encoding rules for that value MUST be applied.
Note that the source XML can contain characters not allowed in "TEXT"
property values. If this is the case, then the XML data MUST be
base64 encoded. As required by [RFC5545], the "ENCODING" property
parameter MUST be present and set to "BASE64", and the "VALUE"
property parameter MUST be present and set to "BINARY".
The ordering of "XML" properties is not preserved in the conversion
between xCal and iCalendar.
Format definition: This property is defined by the following
notation:
xml = "XML" xmlparam ( ":" text ) /
(
";" "ENCODING" "=" "BASE64"
";" "VALUE" "=" "BINARY"
":" binary
)
CRLF
xmlparam = *(";" other-param)
Example: The following is an example of a location embedded in KML
markup inside the "XML" property.
XML:<kml xmlns="http://www.opengis.net/kml/2.2">\n
<Document>\n
<name>KML Sample</name>\n
<open>1</open>\n
<description>An incomplete example of a KML docum
ent - used as an example!</description>\n
</Document>\n
</kml>
5. Handling Unrecognized Properties or Parameters
In iCalendar, properties have a default value type specified by their
definition, e.g., "SUMMARY"'s value type is "TEXT" and "DURATION"'s
is "DURATION". When a property uses its default value type, the
"VALUE" property parameter does not need to be specified on the
property.
When new properties are defined or "X-" properties are used, an
iCalendar<->xCal converter might not recognize them, and know what
the appropriate default value types are, yet they need to be able to
preserve the values. A similar issue arises for unrecognized
property parameters. As a result, the following rules are applied
when dealing with unrecognized properties and property parameters:
o When converting iCalendar into xCal:
* Any property that does not include a "VALUE" property parameter
and whose default value type is not known MUST be converted
using the value type XML element IC:unknown. The content of
that element is the unprocessed value text.
* Any unrecognized property parameter MUST be converted using the
value type XML element IC:unknown, with its content set to the
property parameter value text, treated as if it were a "TEXT"
value or list of "TEXT" values.
o When converting xCal into iCalendar:
* Any IC:unknown property value XML elements are converted
directly into iCalendar values. The containing property MUST
NOT have a "VALUE" property parameter.
* Any IC:unknown parameter value XML elements are converted as if
they were IC:text value type XML elements.
Example: The following is an example of an unrecognized iCalendar
property (that uses a "DATE-TIME" value as its default) and the
equivalent xCal representation of that property.
iCalendar:
X-PROPERTY:20110512T120000Z
xCal:
<x-property>
<unknown>20110512T120000Z</unknown>
</x-property>
Example: The following is an example of an unrecognized iCalendar
property parameter (that uses a "DURATION" value as its default)
specified on a recognized iCalendar property, and the equivalent xCal
representation of that property and property parameter.
iCalendar:
DTSTART;X-PARAM=PT30M:20110512T130000Z
xCal:
<dtstart>
<parameters>
<x-param><unknown>PT30M</unknown></x-param>
</parameters>
<date-time>2011-05-12T13:00:00Z</date-time>
</dtstart>
6. Security Considerations
For security considerations specific to calendar data, see Section 7
of [RFC5545]. Since this specification is a mapping from iCalendar,
no new security concerns are introduced related to calendar data.
The use of XML as a format does have security risks. Section 7 of
[RFC3470] discusses these risks. See also the security discussion
for the application/xml type in [RFC3023].
7. IANA Considerations
This document defines a new URN to identify a new XML namespace for
iCalendar data. The URN conforms to a registry mechanism described
in [RFC3688].
This document defines a new media type. The registration is in
Section 7.2.
This document defines a new property for iCalendar. The registration
is in Section 7.3.
7.1. Namespace Registration
Registration request for the iCalendar namespace:
URI: urn:ietf:params:xml:ns:icalendar-2.0
Registrant Contact: See the "Authors' Addresses" section of this
document.
XML: None. Namespace URIs do not represent an XML specification.
7.2. Media Type
This section defines the MIME media type for use with iCalendar in
XML data.
Type name: application
Subtype name: calendar+xml
Required parameters: None
Optional parameters: method, component, and optinfo as defined for
the text/calendar media type in [RFC5545]; charset as defined for
application/xml in [RFC3023]; per [RFC3023], use of the charset
property parameter with the value "utf-8" is STRONGLY RECOMMENDED.
Encoding considerations: Same as encoding considerations of
application/xml as specified in [RFC3023].
Security considerations: See Section 6.
Interoperability considerations: This media type provides an
alternative format for iCalendar data based on XML.
Published specification: This specification.
Applications that use this media type: Applications that currently
make use of the text/calendar media type can use this as an
alternative.
Additional information:
Magic number(s): None
File extension(s): xcs
Macintosh file type code(s): None specified.
Person & email address to contact for further information:
calsify@ietf.org
Intended usage: COMMON
Restrictions on usage: There are no restrictions on where this media
type can be used.
Author: See the "Authors' Addresses" section of this document.
Change controller: IETF
7.3. iCalendar Property Registrations
This document defines the following new iCalendar property to be
added to the registry defined in Section 8.2.3 of [RFC5545]:
+----------+---------+-----------------------+
| Property | Status | Reference |
+----------+---------+-----------------------+
| XML | Current | RFC 6321, Section 4.2 |
+----------+---------+-----------------------+
8. Acknowledgments
The authors would like to thank the following for their valuable
contributions: Toby Considine, Bernard Desruisseaux, Keith Moore,
Filip Navara, Simon Perreault, Arnaud Quillaud, Peter Saint-Andre,
and Dave Thewlis. This specification originated from the work of the
XML technical committee of the Calendaring and Scheduling Consortium.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media
Types", RFC 3023, January 2001.
[RFC3470] Hollenbeck, S., Rose, M., and L. Masinter, "Guidelines for
the Use of Extensible Markup Language (XML)
within IETF Protocols", BCP 70, RFC 3470, January 2003.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
January 2004.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006.
[RFC5545] Desruisseaux, B., "Internet Calendaring and Scheduling
Core Object Specification (iCalendar)", RFC 5545,
September 2009.
[W3C.REC-xml-20081126]
Sperberg-McQueen, C., Yergeau, F., Bray, T., Paoli, J.,
and E. Maler, "Extensible Markup Language (XML) 1.0 (Fifth
Edition)", World Wide Web Consortium Recommendation REC-
xml-20081126, November 2008,
<http://www.w3.org/TR/2008/REC-xml-20081126>.
9.2. Informative References
[W3C.REC-xmlschema-2-20041028]
Malhotra, A. and P. Biron, "XML Schema Part 2: Datatypes
Second Edition", World Wide Web Consortium
Recommendation REC-xmlschema-2-20041028, October 2004,
<http://www.w3.org/TR/2004/REC-xmlschema-2-20041028>.
Appendix A. RELAX NG Schema
Below is a RELAX NG schema for iCalendar in XML. The schema is non-
normative and given for reference only.
This schema uses the compact notation of RELAX NG. The numeric
section numbers given in the comments refer to sections in [RFC5545].
The ordering of elements follows the section ordering of [RFC5545].
The RELAX NG compact notation "?" operator is used to indicate an
unordered list of items. However, that operator, as defined, allows
"mixing" each element that it operates on at any depth within the
other elements, rather than just allowing "mixing" of siblings only.
As a result, the schema provided allows certain constructs that are
not allowed in iCalendar. Given that there is no sibling-only
unordered list operator in RELAX NG, this is the best representation
that can be given.
Patterns for date/time, duration, and UTC offset values are given
because those differ from the values used in iCalendar. More
restrictive schema with patterns and numerical limits could be
derived from the example schema here if more comprehensive schema
validation is required.
# RELAX NG Schema for iCalendar in XML
default namespace = "urn:ietf:params:xml:ns:icalendar-2.0"
# 3.2 Property Parameters
# 3.2.1 Alternate Text Representation
altrepparam = element altrep {
value-uri
}
# 3.2.2 Common Name
cnparam = element cn {
value-text
}
# 3.2.3 Calendar User Type
cutypeparam = element cutype {
element text {
"INDIVIDUAL" |
"GROUP" |
"RESOURCE" |
"ROOM" |
"UNKNOWN"
}
}
# 3.2.4 Delegators
delfromparam = element delegated-from {
value-cal-address+
}
# 3.2.5 Delegatees
deltoparam = element delegated-to {
value-cal-address+
}
# 3.2.6 Directory Entry Reference
dirparam = element dir {
value-uri
}
# 3.2.7 Inline Encoding
encodingparam = element encoding {
element text {
"8BIT" |
"BASE64"
}
}
# 3.2.8 Format Type
fmttypeparam = element fmttype {
value-text
}
# 3.2.9 Free/Busy Time Type
fbtypeparam = element fbtype {
element text {
"FREE" |
"BUSY" |
"BUSY-UNAVAILABLE" |
"BUSY-TENTATIVE"
}
}
# 3.2.10 Language
languageparam = element language {
value-text
}
# 3.2.11 Group or List Membership
memberparam = element member {
value-cal-address+
}
# 3.2.12 Participation Status
partstatparam = element partstat {
type-partstat-event |
type-partstat-todo |
type-partstat-jour
}
type-partstat-event = (
element text {
"NEEDS-ACTION" |
"ACCEPTED" |
"DECLINED" |
"TENTATIVE" |
"DELEGATED"
}
)
type-partstat-todo = (
element text {
"NEEDS-ACTION" |
"ACCEPTED" |
"DECLINED" |
"TENTATIVE" |
"DELEGATED" |
"COMPLETED" |
"IN-PROCESS"
}
)
type-partstat-jour = (
element text {
"NEEDS-ACTION" |
"ACCEPTED" |
"DECLINED"
}
)
# 3.2.13 Recurrence Identifier Range
rangeparam = element range {
element text {
"THISANDFUTURE"
}
}
# 3.2.14 Alarm Trigger Relationship
trigrelparam = element related {
element text {
"START" |
"END"
}
}
# 3.2.15 Relationship Type
reltypeparam = element reltype {
element text {
"PARENT" |
"CHILD" |
"SIBLING"
}
}
# 3.2.16 Participation Role
roleparam = element role {
element text {
"CHAIR" |
"REQ-PARTICIPANT" |
"OPT-PARTICIPANT" |
"NON-PARTICIPANT"
}
}
# 3.2.17 RSVP Expectation
rsvpparam = element rsvp {
value-boolean
}
# 3.2.18 Sent By
sentbyparam = element sent-by {
value-cal-address
}
# 3.2.19 Time Zone Identifier
tzidparam = element tzid {
value-text
}
# 3.3 Property Value Data Types
# 3.3.1 BINARY
value-binary = element binary {
xsd:string
}
# 3.3.2 BOOLEAN
value-boolean = element boolean {
xsd:boolean
}
# 3.3.3 CAL-ADDRESS
value-cal-address = element cal-address {
xsd:anyURI
}
# 3.3.4 DATE
pattern-date = xsd:string {
pattern = "\d\d\d\d-\d\d-\d\d"
}
value-date = element date {
pattern-date
}
# 3.3.5 DATE-TIME
pattern-date-time = xsd:string {
pattern = "\d\d\d\d-\d\d-\d\dT\d\d:\d\d:\d\dZ?"
}
value-date-time = element date-time {
pattern-date-time
}
# 3.3.6 DURATION
pattern-duration = xsd:string {
pattern = "(+|-)?P(\d+W)|(\d+D)?"
~ "(T(\d+H(\d+M)?(\d+S)?)|"
~ "(\d+M(\d+S)?)|"
~ "(\d+S))?"
}
value-duration = element duration {
pattern-duration
}
# 3.3.7 FLOAT
value-float = element float {
xsd:float
}
# 3.3.8 INTEGER
value-integer = element integer {
xsd:integer
}
# 3.3.9 PERIOD
value-period = element period {
element start {
pattern-date-time
},
(
element end {
pattern-date-time
} |
element duration {
pattern-duration
}
)
}
# 3.3.10 RECUR
value-recur = element recur {
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-freq = element freq {
"SECONDLY" |
"MINUTELY" |
"HOURLY" |
"DAILY" |
"WEEKLY" |
"MONTHLY" |
"YEARLY"
}
type-until = element until {
type-date |
type-date-time
}
type-count = element count {
xsd:positiveInteger
}
type-bysecond = element bysecond {
xsd:nonNegativeInteger
}
type-byminute = element byminute {
xsd:nonNegativeInteger
}
type-byhour = element byhour {
xsd:nonNegativeInteger
}
EID 3050 (Verified) is as follows:Section: Appendix A
Original Text:
type-bysecond = element bysecond {
xsd:positiveInteger
}
type-byminute = element byminute {
xsd:positiveInteger
}
type-byhour = element byhour {
xsd:positiveInteger
}
Corrected Text:
type-bysecond = element bysecond {
xsd:nonNegativeInteger
}
type-byminute = element byminute {
xsd:nonNegativeInteger
}
type-byhour = element byhour {
xsd:nonNegativeInteger
}
Notes:
Those values can be 0 (per RFC 5545) and xsd:positiveInteger doesn't allow that.
Notes:
The default value type of DTSTART is DATE-TIME. The definition of DATE-TIME makes the time portion mandatory. By declaring the value type explicitly, this solution makes the value legal and matches the xCal sample in B.1.2
Another solution is to change the property value to match the default DATE-TIME type DTSTART:20081006T191224Z and adjust the xCal example in B.1.2 to match <dtstart> <date-time>2008-10-06T19:12:24Z</date-time> </dtstart>
EID 2929 (Verified) is as follows:Section: B.2.1.
Original Text:
VERSION:2.0
PRODID:-//Example Corp.//Example Client//EN
BEGIN:VTIMEZONE
Corrected Text:
BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Example Inc.//Example Client//EN
BEGIN:VTIMEZONE
Notes:
Example Inc. is used in all examples, especially in Section B.2.2, the matching XML Data. Also, the BEGIN:VCALENDAR is missing.
LAST-MODIFIED:20040110T032845Z
TZID:US/Eastern
BEGIN:DAYLIGHT
DTSTART:20000404T020000
RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4
TZNAME:EDT
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
END:DAYLIGHT
BEGIN:STANDARD
DTSTART:20001026T020000
RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
TZNAME:EST
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
DTSTAMP:20060206T001121Z
DTSTART;TZID=US/Eastern:20060102T120000
DURATION:PT1H
RRULE:FREQ=DAILY;COUNT=5
RDATE;TZID=US/Eastern;VALUE=PERIOD:20060102T150000/PT2H
SUMMARY:Event #2
DESCRIPTION:We are having a meeting all this week at 12 pm fo
r one hour\, with an additional meeting on the first day 2 h
ours long.\nPlease bring your own lunch for the 12 pm meetin
gs.
UID:00959BC664CA650E933C892C@example.com
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20060206T001121Z
DTSTART;TZID=US/Eastern:20060104T140000
DURATION:PT1H
RECURRENCE-ID;TZID=US/Eastern:20060104T120000
SUMMARY:Event #2 bis
UID:00959BC664CA650E933C892C@example.com
END:VEVENT
END:VCALENDAR
B.2.2. XML Data
<?xml version="1.0" encoding="utf-8" ?>
<icalendar xmlns="urn:ietf:params:xml:ns:icalendar-2.0">
<vcalendar>
<properties>
<prodid>
<text>-//Example Inc.//Example Client//EN</text>
</prodid>
<version>
<text>2.0</text>
</version>
</properties>
<components>
<vtimezone>
<properties>
<last-modified>
<date-time>2004-01-10T03:28:45Z</date-time>
</last-modified>
<tzid><text>US/Eastern</text></tzid>
EID 3679 (Verified) is as follows:Section: B.2.2
Original Text:
<tzid>US/Eastern</tzid>
Corrected Text:
<tzid><text>US/Eastern</text></tzid>
Notes:
The "tzid" property in the second example (p.51) is not formatted correctly. The property value should be enclosed in a "<text>" element.
</properties>
<components>
<daylight>
<properties>
<dtstart>
<date-time>2000-04-04T02:00:00</date-time>
</dtstart>
<rrule>
<recur>
<freq>YEARLY</freq>
<byday>1SU</byday>
<bymonth>4</bymonth>
</recur>
</rrule>
<tzname>
<text>EDT</text>
</tzname>
<tzoffsetfrom>
<utc-offset>-05:00</utc-offset>
</tzoffsetfrom>
<tzoffsetto>
<utc-offset>-04:00</utc-offset>
</tzoffsetto>
</properties>
</daylight>
<standard>
<properties>
<dtstart>
<date-time>2000-10-26T02:00:00</date-time>
</dtstart>
<rrule>
<recur>
<freq>YEARLY</freq>
<byday>-1SU</byday>
<bymonth>10</bymonth>
</recur>
</rrule>
<tzname>
<text>EST</text>
</tzname>
<tzoffsetfrom>
<utc-offset>-04:00</utc-offset>
</tzoffsetfrom>
<tzoffsetto>
<utc-offset>-05:00</utc-offset>
</tzoffsetto>
</properties>
</standard>
</components>
</vtimezone>
<vevent>
<properties>
<dtstamp>
<date-time>2006-02-06T00:11:21Z</date-time>
</dtstamp>
<dtstart>
<parameters>
<tzid><text>US/Eastern</text></tzid>
</parameters>
<date-time>2006-01-02T12:00:00</date-time>
</dtstart>
<duration>
<duration>PT1H</duration>
</duration>
<rrule>
<recur>
<freq>DAILY</freq>
<count>5</count>
</recur>
</rrule>
<rdate>
<parameters>
<tzid><text>US/Eastern</text></tzid>
</parameters>
<period>
<start>2006-01-02T15:00:00</start>
<duration>PT2H</duration>
</period>
</rdate>
<summary>
<text>Event #2</text>
</summary>
<description>
<text>We are having a meeting all this week at 12
pm for one hour, with an additional meeting on the first day
2 hours long.
Please bring your own lunch for the 12 pm
meetings.</text>
</description>
<uid>
<text>00959BC664CA650E933C892C@example.com</text>
</uid>
</properties>
</vevent>
<vevent>
<properties>
<dtstamp>
<date-time>2006-02-06T00:11:21Z</date-time>
</dtstamp>
<dtstart>
<parameters>
<tzid><text>US/Eastern</text></tzid>
</parameters>
<date-time>2006-01-04T14:00:00</date-time>
</dtstart>
<duration>
<duration>PT1H</duration>
</duration>
<recurrence-id>
<parameters>
<tzid><text>US/Eastern</text></tzid>
</parameters>
<date-time>2006-01-04T12:00:00</date-time>
</recurrence-id>
<summary>
<text>Event #2 bis</text>
</summary>
<uid>
<text>00959BC664CA650E933C892C@example.com</text>
</uid>
</properties>
</vevent>
</components>
</vcalendar>
</icalendar>
Authors' Addresses
Cyrus Daboo
Apple Inc.
1 Infinite Loop
Cupertino, CA 95014
USA
EMail: cyrus@daboo.name
URI: http://www.apple.com/
Mike Douglass
Rensselaer Polytechnic Institute
110 8th Street
Troy, NY 12180
USA
EMail: douglm@rpi.edu
URI: http://www.rpi.edu/
Steven Lees
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
USA
EMail: steven.lees@microsoft.com
URI: http://www.microsoft.com/