SIMPLE J. Rosenberg
Internet-Draft dynamicsoft
Expires: August 15, 2004 February 15, 2004
An Extensible Markup Language (XML) Format for Representing Resource
Lists
draft-ietf-simple-xcap-list-usage-02
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Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
In multimedia communications, presence and instant messaging systems,
there is a need to represent lists of Uniform Resource Identifiers
(URIs). These lists, which typically reside on a server, can be
subscribed to, in order to learn the presence status of a group of
users. A Session Initiation Protocol (SIP) INVITE message can be sent
to them, causing the creation of a conference call. This
specification defines an Extensible Markup Language (XML) document
format for representing resource lists. Such a document can be
manipulated by clients using the XML Configuration Access Protocol
(XCAP), although other techniques are permitted.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Structure of a Resource List . . . . . . . . . . . . . . . . . 5
4. XML Schema . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5. Example Document . . . . . . . . . . . . . . . . . . . . . . . 9
6. Usage with XCAP . . . . . . . . . . . . . . . . . . . . . . . 10
6.1 Application Unique ID . . . . . . . . . . . . . . . . . . . . 10
6.2 MIME Type . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6.3 XML Schema . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6.4 Additional Constraints . . . . . . . . . . . . . . . . . . . . 10
6.5 Data Semantics . . . . . . . . . . . . . . . . . . . . . . . . 10
6.6 Naming Conventions . . . . . . . . . . . . . . . . . . . . . . 10
6.7 Resource Interdependencies . . . . . . . . . . . . . . . . . . 10
6.8 Authorization Policies . . . . . . . . . . . . . . . . . . . . 11
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
8.1 XCAP Application Usage ID . . . . . . . . . . . . . . . . . . 13
8.2 application/resource-lists+xml MIME Type . . . . . . . . . . . 13
8.3 URN Sub-Namespace Registration for
urn:ietf:params:xml:ns:resource-lists . . . . . . . . . . . . 14
8.4 Resource List Schema Registration . . . . . . . . . . . . . . 15
Normative References . . . . . . . . . . . . . . . . . . . . . 16
Informative References . . . . . . . . . . . . . . . . . . . . 17
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 17
Intellectual Property and Copyright Statements . . . . . . . . 18
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1. Introduction
In multimedia communications, presence and instant messaging systems,
operations are frequently performed on lists of Uniform Resource
Identifiers (URIs). One such example is a presence list [13]. These
lists are used by Session Initiation Protocol (SIP) for Instant
Messaging and Presence (SIMPLE) [9]Resource List Servers (RLS) [11]
for processing list subscriptions. A presence list can also be used
by a user agent that chooses to subscribe to each user in its
presence list, rather than using a list subscription. In such a case,
the client would read the list from local storage, and generate
subscriptions to each member.
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.
There are other applications of resource lists besides presence
lists. Another example is a list of recipients for an instant
message, or a list of users to invite to a conference bridge.
This specification describes a common format for representing such a
list, and for describing the set of actions which may be performed
against the list. Lists can be hierarchical, and can contain
sub-lists referenced by a URI.
Resource list documents can be manipulated by clients using several
means. One such mechanism is the XML Configuration Access Protocol
(XCAP) [7]. This specification defines the details necessary for
using XCAP to manage presence authorization documents.
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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. Structure of a Resource List
A resource list is an XML [2] document that MUST be well-formed and
SHOULD be valid. Resource 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 resource 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 RFC 3688 [6]. This URN is:
urn:ietf:params:xml:ns:resource-lists
A resource list document begins with the root element tag
"resource-lists". It consists of an optional "mandatory-ns" element
(defined in XCAP [7]), followed by any number of "list" sub-elements,
each of which is a resource 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 the "list" element. The first is
"name". This attribute is a descriptive name for the list. It MUST be
unique amongst all other list elements within the same parent
element. It serves as a useful, but optional handle to identify a
list.
Each list element will also have boolean attributes which indicate a
specific action that may be made against that list. This
specification defines a single attribute - "subscribeable" - which
indicates that the list may be subscribed to using the SIP event list
specification [11]. This application usage does not provide any
information on which users would be authorized to subscribe to the
list, however.
Extensions to this application usage MAY define additional boolean
elements, each within a different namespace, for the purposes of
indicating other actions that may be peformed. When an attribute is
absent, it implies that the operation is not supported.
The third other attribute, "uri" MAY be present. It provides a URI
that can be used to access the list, for example, using the SIP event
notification extension for lists [11]. As a result, the URI MUST be
either a SIP URI or a pres URI [12].
Each "list" element is composed of a sequence of zero or more
elements, each of which may be an "entry" element, a "list" element,
an "entry-ref" element, or an "external" element. The ability of a
"list" element to contain other "list" elements means that a resource
list can be hierarchically structured. An "entry" element describes a
single URI that is part of the list. An "entry-ref" element allows an
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entry to be included by reference, rather than by value. The content
of "entry-ref" is a URI that points to an "entry" element in this
document or another. This URI MUST be an HTTP URI identifying an XCAP
resource. An "external" element contains a reference to a list stored
on another server. The content of this element MUST also be an HTTP
URI identifying an XCAP resource. A "list" element can also contain
elements from other namespaces, for the purposes of extensibility.
The "entry" element describes a single resource. The "entry" element
has two attributes:
name: This optional attribute is a unique identifier amongst all
other "entry" elements of the same parent.
uri: This mandatory attribute is a URI that is used to access the
resource. 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 "display-name". This
element provides a UTF-8 encoded string, meant for consumption by the
user, that describes the resource. Unlike the "name" attribute of the
entry element, the "display-name" has no uniqueness requirements.
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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4. XML Schema
The following is the XML schema definition of the resource list:
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema targetNamespace="urn:ietf:params:xml:ns:resource-lists"
xmlns:xcap="urn:ietf:params:xml:ns:xcap-must-understand"
xmlns="urn:ietf:params:xml:ns:resource-lists"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
elementFormDefault="qualified" attributeFormDefault="unqualified">
<xs:import namespace="urn:ietf:params:xml:ns:xcap-must-understand"/>
<xs:element name="resource-lists">
<xs:complexType>
<xs:sequence>
<xs:element ref="xcap:mandatory-ns" minOccurs="0"/>
<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" minOccurs="0" maxOccurs="unbounded">
<xs:complexType>
<xs:complexContent>
<xs:extension base="listType"/>
</xs:complexContent>
</xs:complexType>
</xs:element>
<xs:element name="external" type="xs:anyURI" minOccurs="0"
maxOccurs="unbounded"/>
<xs:element name="entry" type="entryType" minOccurs="0"
maxOccurs="unbounded"/>
<xs:element name="entry-ref" type="xs:anyURI" 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="optional"/>
<xs:attribute name="uri" type="xs:anyURI" use="optional"/>
<xs:attribute name="subscribeable" type="xs:boolean" use="optional"/>
<xs:anyAttribute namespace="##other"/>
</xs:complexType>
<xs:complexType name="entryType">
<xs:sequence>
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<xs:element name="display-name" type="display-nameType" minOccurs="0"/>
<xs:any namespace="##other" processContents="lax"
minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
<xs:attribute name="name" type="xs:string" use="optional"/>
<xs:attribute name="uri" type="xs:anyURI" use="required"/>
</xs:complexType>
<xs:simpleType name="display-nameType">
<xs:restriction base="xs:string"/>
</xs:simpleType>
</xs:schema>
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5. Example Document
The following is an example of a document compliant to the schema:
]]>
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6. Usage with XCAP
Resource list documents can be manipulated with XCAP. This section
provides the details necessary for such a usage.
6.1 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 "resource-lists" AUID within the IETF tree,
via the IANA registration in Section 8.
6.2 MIME Type
The MIME type for this document is "application/resource-lists+xml".
6.3 XML Schema
The XML Schema for this document is defined as the sole content of
Section 4.
6.4 Additional Constraints
None.
6.5 Data Semantics
Semantics for the document content are provided in Section 3.
6.6 Naming Conventions
There are no naming conventions that need to be defined for this
application usage. A subscription to a resource 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.
6.7 Resource Interdependencies
An XCAP server supporting this application usage need only worry
about a single data interdependency - the "uri" attribute of the list
element.
If the "uri" attribute is absent in a document written to an XCAP
server, but the "subscribeable" 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.
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A server MUST NOT delete the "uri" attribute, however, should a
client change the subscribeable flag to false after the server has
allocated a URI.
If the "uri" attribute is present in a document written to an XCAP
server, but the URI exists in another document managed by the server,
the document is considered invalid. A server MUST reject such a
request with a 409, and MAY include an XCAP error report in the body
indicating this condition. The server MAY suggest, using the "alt-ns"
element, alternate suggestions for a URI that is not currently
allocated.
6.8 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. It is anticipated
that a future application usage will define which users are allowed
to modify a list resource.
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7. 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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8. IANA Considerations
There are several IANA considerations associated with this
specification.
8.1 XCAP Application Usage ID
This section registers a new XCAP Application Usage ID (AUID)
according to the IANA procedures defined in [7].
Name of the AUID: resource-lists
Description: A resource list application is any application that
needs access to a list of resources, identified by a URI, to which
operations, such as subscriptions, can be applied.
8.2 application/resource-lists+xml MIME Type
MIME media type name: application
MIME subtype name: resource-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 7 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 [11] for
SIP-based presence [9].
Additional Information:
Magic Number: None
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File Extension: .rl 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.
8.3 URN Sub-Namespace Registration for
urn:ietf:params:xml:ns:resource-lists
This section registers a new XML namespace, as per the guidelines in
RFC 3688 [6].
URI: The URI for this namespace is
urn:ietf:params:xml:ns:resource-lists.
Registrant Contact: IETF, SIMPLE working group, (simple@ietf.org),
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>Resource Lists Namespace</title>
</head>
<body>
<h1>Namespace for Resource Lists</h1>
<h2>application/resource-lists+xml</h2>
<p>See <a href="[[[URL of published RFC]]]">RFCXXXX</a>.</p>
</body>
</html>
END
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8.4 Resource List Schema Registration
This section registers an XML schema per the procedures in [6].
URI: please assign.
Registrant Contact: IETF, SIMPLE working group, (simple@ietf.org),
Jonathan Rosenberg (jdrosen@jdrosen.net).
The XML for this schema can be found as the sole content of
Section 4.
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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
FirstEdition 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", BCP 81, RFC 3688, January
2004.
[7] Rosenberg, J., "The Extensible Markup Language (XML)
Configuration Access Protocol (XCAP)", draft-ietf-simple-xcap-01
(work in progress), October 2003.
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Informative References
[8] Day, M., Rosenberg, J. and H. Sugano, "A Model for Presence and
Instant Messaging", RFC 2778, February 2000.
[9] Rosenberg, J., "A Presence Event Package for the Session
Initiation Protocol (SIP)", draft-ietf-simple-presence-10 (work
in progress), January 2003.
[10] Roach, A., "Session Initiation Protocol (SIP)-Specific Event
Notification", RFC 3265, June 2002.
[11] Roach, A., Rosenberg, J. 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.
[12] Peterson, J., "Common Profile for Presence (CPP)",
draft-ietf-impp-pres-04 (work in progress), October 2003.
[13] Rosenberg, J. and M. Isomaki, "Requirements for Manipulation of
Data Elements in Session Initiation Protocol (SIP) for Instant
Messaging and Presence Leveraging Extensions (SIMPLE) Systems",
draft-ietf-simple-data-req-03 (work in progress), June 2003.
Author's Address
Jonathan Rosenberg
dynamicsoft
600 Lanidex Plaza
Parsippany, NJ 07054
US
Phone: +1 973 952-5000
EMail: jdrosen@dynamicsoft.com
URI: http://www.jdrosen.net
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