Network Working Group H. Schulzrinne
Request for Comments: 4481 Columbia U.
Category: Standards Track July 2006
Timed Presence Extensions to the
Presence Information Data Format (PIDF) to
Indicate Status Information for Past and Future Time Intervals
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
The Presence Information Data Format (PIDF) defines a basic XML
format for presenting presence information for a presentity. This
document extends PIDF, adding a timed status extension
(<timed-status> element) that allows a presentity to declare its
status for a time interval fully in the future or the past.
Table of Contents
1. Introduction ....................................................2
2. Terminology and Conventions .....................................2
3. Timed-Status Element ............................................3
4. Example .........................................................4
5. The XML Schema Definition .......................................5
6. IANA Considerations .............................................6
6.1. URN Sub-Namespace Registration for
'urn:ietf:params:xml:ns:pidf:timed-status' .................6
6.2. Schema Registration for Schema
'urn:ietf:params:xml:ns:pidf:timed-status' .................7
7. Security Considerations .........................................7
8. References ......................................................7
8.1. Normative References .......................................7
8.2. Informative References .....................................7
Contributor's Address ..............................................8
Acknowledgements ...................................................8
Schulzrinne Standards Track [Page 1]RFC 4481 Timed Presence July 2006
1. Introduction
Traditionally, presence information, e.g., represented as Presence
Information Data Format [3] (PIDF) and augmented by Rich Presence
Information Data format [9] (RPID), describes the current state of
the presentity. However, a watcher can better plan communications if
it knows about the presentity's future plans. For example, if a
watcher knows that the presentity is about to travel, it might place
a phone call earlier.
In this document, we use terms defined in RFC 2778 [7]. In
particular, a "presentity", abbreviating presence entity, provides
presence information to a presence service. It is typically a
uniquely-identified person.
RPID already allows a presentity to indicate the period when a
particular aspect of its presence is valid. However, the <status>
element in the PIDF <tuple> does not have this facility, so that it
is not possible to indicate that a presentity will be OPEN or CLOSED
in the future, for example.
It is also occasionally useful to represent past information since it
may be the only known presence information; it may give watchers an
indication of the current status. For example, indicating that the
presentity was at an off-site meeting that ended an hour ago
indicates that the presentity is likely in transit at the current
time.
It is unfortunately not possible to simply add time range attributes
to the PIDF <status> element, as PIDF parsers without this capability
would ignore these attributes and thus not be able to distinguish
current from future presence status information.
This document defines the <timed-status> element that describes the
status of a presentity that is either no longer valid or covers some
future time period.
2. Terminology and Conventions
The key words MUST, MUST NOT, REQUIRED, SHOULD, SHOULD NOT,
RECOMMENDED, MAY, and OPTIONAL in this document are to be interpreted
as described in BCP 14, RFC 2119 [1].
Schulzrinne Standards Track [Page 2]
RFC 4481 Timed Presence July 2006
3. Timed-Status Element
The <timed-status> element is a child of the <tuple> element and MUST
NOT appear as a child of a PIDF <status> element or another
<timed-status> element. More than one such element MAY appear within
a PIDF <tuple> element.
Sources of <timed-status> information should avoid elements that
overlap in time, but since overlapping appointments are common in
calendars, for example, receivers MUST be able to render such
overlapping <timed-status> indications.
The <timed-status> element MUST be qualified with the 'from'
attribute and MAY be qualified with an 'until' attribute to describe
the time when the status assumed this value and the time until which
this element is expected to be valid. If the 'until' attribute is
missing, the information is assumed valid until the tuple is
explicitly overridden or expires as defined by the publication
mechanism used. The time range MUST NOT encompass the present time,
i.e., the PIDF <timestamp> value, as that would provide an
unnecessary and confusing alternate mechanism to describe presence.
Thus, the 'from' attribute for tuples without an 'until' attribute
MUST refer to the future.
During composition, a presence agent (PA) may encounter a stored
<timed-status> element that covers the present time. The PA MAY
either discard that element or MAY convert it to a regular <status>
element if it considers that information more credible.
The <timed-status> element may contain the <basic> and <note>
elements, as well as any other element that is appropriate as a PIDF
<status> extension and that has a limited validity period. Examples
include the PIDF-LO [8] extensions for location objects.
This extension chose absolute rather than relative times, since
relative times would be too hard to keep properly updated when
spacing notifications, for example. Originators of presence
information MUST generate time values in the <timed-status> elements
that are fully in the past or future relative to local real
(wallclock) time and the time information contained in the optional
PIDF <timestamp> element.
Schulzrinne Standards Track [Page 3]
RFC 4481 Timed Presence July 2006
4. Example
An example combining PIDF and timed-status is shown below:
<presence xmlns="urn:ietf:params:xml:ns:pidf"
xmlns:ts="urn:ietf:params:xml:ns:pidf:timed-status"
entity="pres:someone@example.com">
<tuple id="c8dqui">
<status>
<basic>open</basic>
</status>
<ts:timed-status from="2005-08-15T10:20:00.000-05:00"
until="2005-08-22T19:30:00.000-05:00">
<ts:basic>closed</ts:basic>
</ts:timed-status>
<contact>sip:someone@example.com</contact>
</tuple>
<note>I'll be in Tokyo next week</note>
</presence>
Schulzrinne Standards Track [Page 4]RFC 4481 Timed Presence July 2006
5. The XML Schema Definition
The XML [4] schema [5][6] is shown below.
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:ts="urn:ietf:params:xml:ns:pidf:timed-status"
xmlns:pidf="urn:ietf:params:xml:ns:pidf"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
targetNamespace="urn:ietf:params:xml:ns:pidf:timed-status"
elementFormDefault="qualified" attributeFormDefault="unqualified">
<xs:import namespace="urn:ietf:params:xml:ns:pidf"/>
<xs:annotation>
<xs:documentation>
Describes timed-status tuple extensions for PIDF.
</xs:documentation>
</xs:annotation>
<xs:element name="timed-status" type="ts:timed-status"/>
<xs:complexType name="timed-status">
<xs:sequence>
<xs:element name="basic" type="pidf:basic" minOccurs="0"/>
<xs:element name="note" type="pidf:note" minOccurs="0"/>
<xs:any namespace="##other" processContents="lax" minOccurs="0"
maxOccurs="unbounded"/>
</xs:sequence>
<xs:attribute name="from" type="xs:dateTime" use="required"/>
<xs:attribute name="until" type="xs:dateTime"/>
</xs:complexType>
</xs:schema>
Schulzrinne Standards Track [Page 5]RFC 4481 Timed Presence July 2006
6. IANA Considerations
This document calls for IANA to register a new XML namespace URN and
schema per [2].
6.1. URN Sub-Namespace Registration for
'urn:ietf:params:xml:ns:pidf:timed-status'
URI: urn:ietf:params:xml:ns:pidf:timed-status
Description: This is the XML namespace for XML elements defined by
RFC 4481 to describe timed-status presence information extensions
for the status element in the PIDF presence document format in the
application/pidf+xml content type.
Registrant Contact: IETF, SIMPLE working group, simple@ietf.org;
Henning Schulzrinne, hgs@cs.columbia.edu
XML:
BEGIN
<?xml version="1.0"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"
"http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">
<html xmlns="http://www.w3.org/1999/xhtml
<head>
<meta http-equiv="content-type"
content="text/html;charset=iso-8859-1"/>
<title>Timed Presence Extensions to the Presence
Information Data Format (PIDF) to Indicate Status
Information for Past and Future Time Intervals</title>
</head>
<body>
<h1>Namespace for timed-status presence extension</h1>
<h2>urn:ietf:params:xml:ns:pidf:timed-status</h2>
<p>See <a href="http://www.rfc-editor.org/rfc/rfc4481.txt">
RFC4481</a>.</p>
</body>
</html>
END
Schulzrinne Standards Track [Page 6]RFC 4481 Timed Presence July 2006
6.2. Schema Registration for Schema
'urn:ietf:params:xml:ns:pidf:timed-status'
URI: urn:ietf:params:xml:ns:pidf:timed-status
Registrant Contact: IESG
XML: See Section 5
7. Security Considerations
The security issues are similar to those for RPID [9].
8. References
8.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, January
2004.
[3] Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr, W., and
J. Peterson, "Presence Information Data Format (PIDF)", RFC
3863, August 2004.
[4] Yergeau, F., Paoli, J., Sperberg-McQueen, C., Bray, T., and E.
Maler, "Extensible Markup Language (XML) 1.0 (Third Edition)",
W3C REC REC-xml-20040204, February 2004.
[5] Maloney, M., Beech, D., Thompson, H., and N. Mendelsohn, "XML
Schema Part 1: Structures Second Edition", W3C REC REC-
xmlschema-1-20041028, October 2004.
[6] Malhotra, A. and P. Biron, "XML Schema Part 2: Datatypes Second
Edition", W3C REC REC-xmlschema-2-20041028, October 2004.
8.2. Informative References
[7] Day, M., Rosenberg, J., and H. Sugano, "A Model for Presence and
Instant Messaging", RFC 2778, February 2000.
[8] Peterson, J., "A Presence-based GEOPRIV Location Object Format",
RFC 4119, December 2005.
Schulzrinne Standards Track [Page 7]RFC 4481 Timed Presence July 2006
[9] Schulzrinne, H., Gurbani, V., Kyzivat, P., and J. Rosenberg,
"RPID: Rich Presence Extensions to the Presence Information Data
Format (PIDF)", RFC 4480, July 2006.
Contributor's Address
Jonathan Rosenberg
dynamicsoft
600 Lanidex Plaza
Parsippany, NJ 07054-2711
USA
EMail: jdrosen@dynamicsoft.com
Acknowledgements
This document is based on the discussions within the IETF SIMPLE
working group. Mary Barnes, Avri Doria, Miguel Garcia, Vijay
Gurbani, Hisham Khartabil, Paul Kyzivat, Mikko Lonnfors, Yannis
Pavlidis and Jon Peterson provided helpful comments.
Author's Address
Henning Schulzrinne
Columbia University
Department of Computer Science
450 Computer Science Building
New York, NY 10027
US
Phone: +1 212 939 7004
EMail: hgs+simple@cs.columbia.edu
URI: http://www.cs.columbia.edu
Schulzrinne Standards Track [Page 8]RFC 4481 Timed Presence July 2006
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Schulzrinne Standards Track [Page 9]
