Timed Presence Extensions to the Presence Information Data Format (PIDF) to Indicate Status Information for Past and Future Time Intervals
A PIDF extension that lets a presentity announce its status for a time span that is entirely in the past or the future.
Schulzrinne, H., "Timed Presence Extensions to the Presence Information Data Format (PIDF) to Indicate Status Information for Past and Future Time Intervals", RFC 4481, DOI 10.17487/RFC4481, July 2006, <https://www.rfc-editor.org/info/rfc4481>.
@misc{rfc4481,
series = {Request for Comments},
number = 4481,
howpublished = {RFC 4481},
publisher = {RFC Editor},
doi = {10.17487/RFC4481},
url = {https://www.rfc-editor.org/info/rfc4481},
author = {H. Schulzrinne},
title = {{Timed Presence Extensions to the Presence Information Data Format (PIDF) to Indicate Status Information for Past and Future Time Intervals}},
pagetotal = 9,
year = 2006,
month = jul,
} RFC text
Contents
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
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].
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.
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>
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>
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
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.
[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
Full Copyright Statement
Copyright (C) The Internet Society (2006).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Acknowledgement
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).
AI ELI5
On this page
§1Why Presence Needs a Time Range
The Presence Information Data Format (PIDF) is a basic XML format for describing the presence of a presentity, short for presence entity, which is typically a uniquely identified person. Traditionally, PIDF and its rich extension RPID (RFC 4480) describe only the current state of the presentity.
The RFC argues that a watcher can plan better if it knows the presentity's future plans. For example, a watcher who knows the presentity is about to travel might place a phone call earlier. Past information can also help: knowing the presentity was at an off-site meeting that ended an hour ago suggests it is probably in transit now.
RPID can already say when one aspect of presence is valid, but the PIDF <status> element cannot, so there is no way to say a presentity will be OPEN or CLOSED in the future.
Your friends usually see only what you are doing this minute. This lets you also tell them what you will be doing later, or what you were doing a little while ago.
§2Why a New Element Instead of Attributes
The RFC explains why it does not just add time attributes to the existing <status> element. PIDF parsers that do not understand the new attributes would ignore them, and so could not tell current status from future status. A reader without the extension would treat a future CLOSED as the present.
Instead, the document defines a separate <timed-status> element for status that is either no longer valid or covers a future period. Old parsers simply do not see it as the current status.
The extension also chose absolute times rather than relative ones, because relative times would be too hard to keep properly updated when spacing notifications.
If you scribbled a date on an old sign, someone who could not read the scribble would think the sign was current. A separate new sign avoids the mix-up.
§3The timed-status Element
The <timed-status> element is a child of the PIDF <tuple>. It MUST NOT appear inside a PIDF <status> element or inside another <timed-status>. More than one may appear in a tuple.
It MUST carry a from attribute and MAY carry an until attribute. They give the time the status took on this value and the time until which it is expected to be valid. Without until, the information is assumed valid until the tuple is explicitly overridden or expires under the publication mechanism in use.
Inside the element can sit <basic> and <note>, plus any other element that suits a PIDF status extension and has a limited validity period. The PIDF-LO location extensions (RFC 4119) are given as an example.
Each note says when it starts and, if you want, when it ends. Inside it you write the status, like open or closed, and maybe a little message.
§4Rules for Time Ranges and Overlaps
The time range MUST NOT encompass the present time, meaning the PIDF <timestamp> value. Otherwise it would offer an unnecessary and confusing second way to describe current presence. So a <timed-status> without until must have a from that lies in the future. Originators MUST produce times fully in the past or future relative to local wallclock time and any PIDF timestamp.
Sources should avoid overlapping elements, but overlapping appointments are common in calendars, so receivers MUST be able to render overlapping indications.
While composing a document, a presence agent (PA) may find a stored <timed-status> that covers the present. It MAY discard it, or convert it to a regular <status> if it considers that information more credible.
A note must be about before or after now, never about right now, because right now already has its own place. If two calendar entries overlap, the viewer must still be able to show both.
§5An Example Document
The RFC's example is a PIDF document for pres:someone@example.com. The tuple has a normal <status> with <basic>open</basic>, so the person is open now. A <ts:timed-status> with from 2005-08-15T10:20:00.000-05:00 and until 2005-08-22T19:30:00.000-05:00 contains <ts:basic>closed</ts:basic>. The presence document's own note says "I'll be in Tokyo next week".
Read together: open today, closed for the week ahead.
Today the sign says open. A second sign says closed from one Monday to the next, and a note explains the person is traveling.
<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>§6XML Schema and IANA Registrations
The schema defines timed-status in the namespace urn:ietf:params:xml:ns:pidf:timed-status. Its content is an optional basic, an optional note, and any number of elements from other namespaces. The from attribute is required and typed as an XML Schema dateTime; until is optional with the same type.
IANA is asked to register that namespace URN and the schema, following the IETF XML Registry (RFC 3688). The registrant contact is the IETF SIMPLE working group, and the schema registrant is the IESG.
The rules are written in a strict form computers can check, and the name of the extension is put on an official list so nobody else uses it.
§7Security Considerations
The RFC's whole security section is one sentence: the security issues are similar to those for RPID (RFC 4480). It adds no mechanisms of its own.
This note has the same safety worries as the other presence add-ons, so the authors point there instead of repeating them.