SIMPLE J. Rosenberg
Internet-Draft dynamicsoft
Expires: December 22, 2003 June 23, 2003
An Extensible Markup Language (XML) Configuration Access Protocol
(XCAP) Usage for Presence Lists
draft-ietf-simple-xcap-list-usage-00
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Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This document describes a usage of the Extensible Markup Language
(XML) Configuration Access Protocol (XCAP) for manipulating lists of
presentities (also known as buddy lists or rosters). It does so by
specifying an XML Schema that contains a list of presentities that a
user is interested in watching.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Application Unique ID . . . . . . . . . . . . . . . . . . . 5
4. Structure of a Presence List . . . . . . . . . . . . . . . . 6
5. Computed Data . . . . . . . . . . . . . . . . . . . . . . . 8
6. Additional Constraints . . . . . . . . . . . . . . . . . . . 9
7. Naming Conventions . . . . . . . . . . . . . . . . . . . . . 10
8. Authorization Policies . . . . . . . . . . . . . . . . . . . 11
9. XML Schema . . . . . . . . . . . . . . . . . . . . . . . . . 12
10. Example Document . . . . . . . . . . . . . . . . . . . . . . 13
11. Security Considerations . . . . . . . . . . . . . . . . . . 14
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . 15
12.1 XCAP Application Usage ID . . . . . . . . . . . . . . . . . 15
12.2 application/presence-lists+xml MIME Type . . . . . . . . . . 15
12.3 URN Sub-Namespace Registration for
urn:ietf:params:xml:ns:presence-lists . . . . . . . . . . . 16
Normative References . . . . . . . . . . . . . . . . . . . . 17
Informative References . . . . . . . . . . . . . . . . . . . 18
Author's Address . . . . . . . . . . . . . . . . . . . . . . 18
Intellectual Property and Copyright Statements . . . . . . . 19
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1. Introduction
The Session Initiation Protocol (SIP) for Instant Messaging and
Presence (SIMPLE) specifications allow a user, called a watcher, to
subscribe to another user, called a presentity [7], in order to learn
their presence information [8]. In many cases, a watcher will be
interested in not just a single presentity, but a list of
presentities. Such a list of presentities is called a presence list.
When a user wants to subscribe to their presence list, the procedures
in [8] require the watcher to create and manage a subscription for
each presentity in their list. For large lists, the bandwidth
required to do this can be a problem, particularly for wireless
networks. An extension to the SIP events framework [9] has been
defined. The extension allows a watcher to subscribe to a list of
resources, using a single subscription [10]. This mechanism assumes
that a server, called the Resource List Server (RLS) has a copy of
the presence list that the user wishes to subscribe to. By using
protocols such as the XML Configuration Access Protocol (XCAP) [12],
a client can place this list on the server, and manipulate it as
needed.
XCAP requires application usages to standardize several pieces of
information, including an application unique ID (AUID), an XML
schema, and various other pieces of information. This specification
fulfills those requirements.
The XML schema defined here has several other usages outside of XCAP:
1. A PC client application will need to know the users in the
presence list, so that it can generate a subscription to each
one. This information represents user provisioned data for the
application. Typically, this information is stored on local disk
in a proprietary file format. By defining a standard format, the
same list can be used by a multiplicity of different client
applications, providing portability across them.
2. It is common for users to share presence lists. As an example,
user A may have three people in their list that they wish to tell
user B about. User A would like to send an email to user B with
an attachment describing these three people. Should user B open
the attachment, the three people can be added to their own
presence list. Doing this requires a standardized format for
exchanging lists over email, instant messaging, and other
communications protocols.
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2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in RFC 2119 [1] and
indicate requirement levels for compliant implementations.
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3. Application Unique ID
XCAP requires application usages to define a unique application usage
ID (AUID) in either the IETF tree or a vendor tree. This
specification defines the "presence-lists" AUID within the IETF tree,
via the IANA registration in Section 12.
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4. Structure of a Presence List
A presence list is an XML [2] document that MUST be well-formed and
SHOULD be valid. Presence list documents MUST be based on XML 1.0 and
MUST be encoded using UTF-8. This specification makes use of XML
namespaces for identifying presence list documents and document
fragments. The namespace URI for elements defined by this
specification is a URN [3], using the namespace identifier 'ietf'
defined by [5] and extended by [6]. This URN is:
urn:ietf:params:xml:ns:presence-lists
A presence list document begins with the root element tag
``presence-lists''. It consists of any number of ``list''
sub-elements, each of which is a presence list. Other elements from
different namespaces MAY be present for the purposes of
extensibility; elements or attributes from unknown namespaces MUST be
ignored. There are three attributes associated with this element. The
first two, "name", and "subscribable" MUST be present:
name: This attribute is a descriptive name for the list. It MUST
be unique amongst all other list elements within the same parent
element.
subscribable: This boolean attribute indicates whether or not the
list is subscribable or not.
The other attribute, "uri" MAY be present:
uri: This attribute provides a URI that can be used to subscribe
to the list, using the SIP event notification extension for lists
[10]. As a result, the URI MUST be either a SIP URI or a pres URI
[11]. [[OPEN ISSUE: Do we want this to be a comma separated list,
so that a presence list can have any number of valid aliases?]]
[[OPEN ISSUE: We also need to define policy about who is allowed to
subscribe to the list. We can either integrate that into the list
definition described here, or handle that as a separate policy
specification. The SEACAP proposal kept them together. I believe now
that they should be kept separate.]]
Each list element is composed of a sequence of entry elements or list
elements. The ability of a list element to contain other list
elements means that a presence list can be hierarchically structured.
An entry element describes a single presentity that is part of the
list. A list element can also contain elements from other namespaces,
for the purposes of extensibility.
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The entry element describes a single presentity. The entry element
has two attributes:
name: This mandatory attribute is a unique identifier amongst all
other entry elements of the same parent.
uri: This optional attribute is a URI that is used to subscribe to
the presentity. It MUST be either a SIP or pres URI.
The entry element contains a sequence of other elements. Only one
such element is defined at this time, which is the display-name. This
element provides a UTF-8 encoded string, meant for consumption by the
user, that describes the presentity. Unlike the "name" attribute of
the entry element, the display-name has no uniqueness requirements.
[[OPEN ISSUE: Do we need this in addition to the name attribute?]].
Other elements from other namespaces MAY be included. This is meant
to support the inclusion of other information about the entry, such
as a phone number or postal address.
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5. Computed Data
An XCAP server supporting this application usage need only worry
about a single piece of computed data - the "uri" attribute of the
list element.
If the "uri" attribute is absent in a document written to an XCAP
server, but the "subscribable" flag is true, the XCAP server MUST
allocate a URI for this list. This allocated URI MUST be globally
unique, and MUST route to an RLS which will handle list subscriptions
for the list defined by the document. The server MUST set the uri
attribute of the document with this URI.
A server MUST NOT delete the "uri" attribute, however, should a
client change the subscribable flag to false after the server has
allocated a URI.
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6. Additional Constraints
There are no constraints on the document beyond those described in
the schema.
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7. Naming Conventions
There are no naming conventions that need to be defined for this
application usage. A subscription to a presence list will be to a
specific URI. That URI will be one of the "uri" attributes defined in
a list within one of the documents managed by an XCAP server.
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8. Authorization Policies
This application usage does not modify the default XCAP authorization
policy, which is that only a user can read, write or modify their own
documents. A server can allow priveleged users to modify documents
that they don't own, but the establishment and indication of such
policies is outside the scope of this document.
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9. XML Schema
The following is the XML schema definition of the presence list:
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
elementFormDefault="qualified"
attributeFormDefault="unqualified">
<xs:element name="presence-lists">
<xs:complexType>
<xs:sequence>
<xs:element name="list" type="listType" minOccurs="0"
maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:complexType name="listType">
<xs:sequence maxOccurs="unbounded">
<xs:choice>
<xs:element name="list" type="listType" minOccurs="0"
maxOccurs="unbounded"/>
<xs:element name="entry" type="entryType" minOccurs="0"
maxOccurs="unbounded"/>
<xs:any namespace="##other" processContents="lax"
minOccurs="0" maxOccurs="unbounded"/>
</xs:choice>
</xs:sequence>
<xs:attribute name="name" type="xs:string" use="required"/>
<xs:attribute name="uri" type="xs:anyURI" use="optional"/>
<xs:attribute name="subscribable" type="xs:boolean" use="required" />
</xs:complexType>
<xs:complexType name="entryType">
<xs:sequence>
<xs:element name="display-name" type="display-nameType"/>
<xs:any namespace="##other" processContents="lax"
minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
<xs:attribute name="name" type="xs:string" use="required"/>
<xs:attribute name="uri" type="xs:anyURI" use="optional"/>
</xs:complexType>
<xs:simpleType name="display-nameType">
<xs:restriction base="xs:string"/>
</xs:simpleType>
</xs:schema>
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10. Example Document
The following is an example of a document compliant to the schema:
<?xml version="1.0" encoding="UTF-8"?>
<presence-lists xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<list name="friends" uri="sip:friends@example.com" subscribable="true">
<entry name="Bill" uri="sip:bill@example.com">
<display-name>Bill Doe</display-name>
</entry>
<list name="close-friends" uri="sip:close-friends@example.com"
subscribable="true">
<entry name="Joe" uri="sip:joe@example.com">
<display-name>Joe Smith</display-name>
</entry>
<entry name="Nancy" uri="sip:nancy@example.com">
<display-name>Nancy Gross</display-name>
</entry>
</list>
</list>
</presence-lists>
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11. Security Considerations
The configuration information defined by this application usage is
particularly sensitive. It represents the principle set of people
with whom a user would like to communicate. As a result, clients
SHOULD use TLS when contacting servers in order to fetch this
information. Note that this does not represent a change in
requirement strength from XCAP.
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12. IANA Considerations
There are several IANA considerations associated with this
specification.
12.1 XCAP Application Usage ID
This section registers a new XCAP Application Usage ID (AUID)
according to the IANA procedures defined in [12].
Name of the AUID: presence-lists
Description: A presence list application is a usage of the SIP
events framework (RFC 3265) [9] along with its list extension
[10], for subscribing to a list of presentities (RFC2778) [7]
stored at a server.
12.2 application/presence-lists+xml MIME Type
MIME media type name: application
MIME subtype name: presence-lists+xml
Mandatory parameters: none
Optional parameters: Same as charset parameter application/xml as
specified in RFC 3023 [4].
Encoding considerations: Same as encoding considerations of
application/xml as specified in RFC 3023 [4].
Security considerations: See Section 10 of RFC 3023 [4] and
Section 11 of this specification.
Interoperability considerations: none.
Published specification: This document.
Applications which use this media type: This document type has
been used to support subscriptions to lists of users [10] for
SIP-based presence [8].
Additional Information:
Magic Number: None
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File Extension: .pl or .xml
Macintosh file type code: "TEXT"
Personal and email address for further information: Jonathan
Rosenberg, jdrosen@jdrosen.net
Intended usage: COMMON
Author/Change controller: The IETF.
12.3 URN Sub-Namespace Registration for
urn:ietf:params:xml:ns:presence-lists
This section registers a new XML namespace, as per the guidelines in
[6]
URI: The URI for this namespace is
urn:ietf:params:xml:ns:presence-lists.
Registrant Contact: IETF, SIMPLE working group,
(simple@mailman.dynamicsoft.com), Jonathan Rosenberg
(jdrosen@jdrosen.net).
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>Presence Lists Namespace</title>
</head>
<body>
<h1>Namespace for Presence Lists</h1>
<h2>application/presence-lists+xml</h2>
<p>See <a href="[[[URL of published RFC]]]">RFCXXXX</a>.</p>
</body>
</html>
END
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Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Bray, T., Paoli, J., Sperberg-McQueen, C. and E. Maler,
"Extensible Markup Language (XML) 1.0 (Second Edition)", W3C REC
REC-xml-20001006, October 2000.
[3] Moats, R., "URN Syntax", RFC 2141, May 1997.
[4] Murata, M., St. Laurent, S. and D. Kohn, "XML Media Types", RFC
3023, January 2001.
[5] Moats, R., "A URN Namespace for IETF Documents", RFC 2648,
August 1999.
[6] Mealling, M., "The IETF XML Registry",
draft-mealling-iana-xmlns-registry-05 (work in progress), June
2003.
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Informative References
[7] Day, M., Rosenberg, J. and H. Sugano, "A Model for Presence and
Instant Messaging", RFC 2778, February 2000.
[8] Rosenberg, J., "A Presence Event Package for the Session
Initiation Protocol (SIP)", draft-ietf-simple-presence-10 (work
in progress), January 2003.
[9] Roach, A., "Session Initiation Protocol (SIP)-Specific Event
Notification", RFC 3265, June 2002.
[10] Rosenberg, J., Roach, A. and B. Campbell, "A Session Initiation
Protocol (SIP) Event Notification Extension for Resource
Lists", draft-ietf-simple-event-list-04 (work in progress),
June 2003.
[11] Peterson, J., "Common Profile for Presence (CPP)",
draft-ietf-impp-pres-03 (work in progress), May 2003.
[12] Rosenberg, J., "The Extensible Markup Language (XML)
Configuration Access Protocol (XCAP)",
draft-rosenberg-simple-xcap-00 (work in progress), May 2003.
Author's Address
Jonathan Rosenberg
dynamicsoft
600 Lanidex Plaza
Parsippany, NJ 07052
US
Phone: +1 973 952-5000
EMail: jdrosen@dynamicsoft.com
URI: http://www.jdrosen.net
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