SIMPLE                                                      J. Rosenberg
Internet-Draft                                               dynamicsoft
Expires: December 22, 2003                                 June 23, April 26, 2004                                 October 27, 2003

   An Extensible Markup Language (XML) Configuration Access Protocol
                    (XCAP) Usage for Presence Resource Lists

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

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Copyright Notice

   Copyright (C) The Internet Society (2003). All Rights Reserved.


   This document describes a usage of the Extensible Markup Language
   (XML) Configuration Access Protocol (XCAP) for manipulating lists of
   resources. These lists can be used as presence lists (also known as
   buddy lists or rosters). It rosters), but this specification does so by
   specifying an XML Schema that contains a list of presentities that a
   user is interested in watching. not restrict
   their usage to that.

Table of Contents

   1.   Introduction . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.   Terminology  . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.   Application Unique ID  . . . . . . . . . . . . . . . . . . .   5
   4.   Structure of a Presence Resource List . . . . . . . . . . . . . . . .   6
   5.   Computed Data  . . . . . .   Resource Interdependencies . . . . . . . . . . . . . . . . .   8
   6.   Additional Constraints . . . . . . . . . . . . . . . . . . .   9
   7.   Naming Conventions . . . . . . . . . . . . . . . . . . . . .  10
   8.   Authorization Policies . . . . . . . . . . . . . . . . . . .  11
   9.   XML Schema . . . . . . . . . . . . . . . . . . . . . . . . .  12
   10.  Example Document . . . . . . . . . . . . . . . . . . . . . .  13  14
   11.  Security Considerations  . . . . . . . . . . . . . . . . . .  14  15
   12.  IANA Considerations  . . . . . . . . . . . . . . . . . . . .  15  16
   12.1 XCAP Application Usage ID  . . . . . . . . . . . . . . . . .  15  16
   12.2 application/presence-lists+xml application/resource-lists+xml MIME Type . . . . . . . . . .  15  16
   12.3 URN Sub-Namespace Registration for
        urn:ietf:params:xml:ns:resource-lists  . . . . . . . . . . .  16  17
        Normative References . . . . . . . . . . . . . . . . . . . .  17  18
        Informative References . . . . . . . . . . . . . . . . . . .  18  19
        Author's Address . . . . . . . . . . . . . . . . . . . . . .  18  19
        Intellectual Property and Copyright Statements . . . . . . .  19  20

1. Introduction


   In many communications applications, it is neccesary for the network
   to have access to a list of resources that represent a group that the
   user would like to apply an action to. One such example is a presence
   list [13]. These lists are used by 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 [9]Resource List Servers
   (RLS) [11] for processing list subscriptions. Another example might
   interested in not just a single presentity, but a list of
   presentities. Such recipients for an instant message, or a list of presentities is called a presence list.

   When a user wants to subscribe users to their presence list, the procedures
   in [8] require the watcher
   invite to create and manage a subscription for
   each presentity in their list. For large lists, the bandwidth
   required conference bridge.

   Generally, these lists will need 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 manipulated by the Resource List Server (RLS) has a copy end users
   of the presence list that system, and used by servers in the user wishes to subscribe to. By using
   protocols network. To support such as
   manipulations, the XML Configuration Access Protocol (XCAP) [12],
   a client can place this list on the server, and manipulate it as
   needed. [7] has
   been defined. 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.

2. Terminology

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   and "OPTIONAL" are to be interpreted as described in RFC 2119 [1] and
   indicate requirement levels for compliant implementations.

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" "resource-lists" AUID within the IETF tree,
   via the IANA registration in Section 12.

4. Structure of a Presence Resource List

   A presence resource list is an XML [2] document that MUST be well-formed and
   SHOULD be valid. Presence 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 presence 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 [6]. This URN is:



   A presence resource list document begins with the root element tag
   ``resource-lists''.  It consists of any number of ``list''
   sub-elements, each of which is a presence 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 this element. The
   first two,
   first, "name", and "subscribable" MUST be present:

      name: This attribute is a descriptive name for the list. It MUST list. It MUST
      be unique amongst all other list elements within the same parent

   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 unique amongst all other subscribed to using the SIP event list elements
   specification [11]. Extensions to this application usage MAY define
   additional boolean elements, each within a different namespace, for
   the same parent

      subscribable: This boolean purposes of indicating other actions that may be peformed. When
   an attribute indicates whether or not is absent, it implies that the
      list operation is subscribable or not. not

   The third other attribute, "uri" MAY be present:

      uri: This attribute present. It provides a URI
   that can be used to subscribe
      to access the list, for example, using the SIP event
   notification extension for lists
      [10]. [11]. 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.]] [12].

   Each list element is composed of a sequence of entry elements or elements, list
   elements, external elements. The ability of a list element to contain
   other list elements means that a presence resource list can be hierarchically
   structured. An entry element describes a single presentity that is
   part of the list. An external element contains a reference to a list
   stored on another server. A list element can also contain elements
   from other namespaces, for the purposes of extensibility.

   The entry element describes a single presentity. resource. 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 access the presentity.
      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 the display-name. This
   element provides a UTF-8 encoded string, meant for consumption by the
   user, that describes the presentity. resource. 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.

5. Computed Data Resource Interdependencies

   An XCAP server supporting this application usage need only worry
   about a single piece of computed data interdependency - the "uri" attribute of the list

   If the "uri" attribute is absent in a document written to an XCAP
   server, but the "subscribable" "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.

   A server MUST NOT delete the "uri" attribute, however, should a
   client change the subscribable subscribeable flag to false after the server has
   allocated a URI.

6. Additional Constraints

   There are no constraints on the document beyond those described in
   the schema.

7. Naming Conventions

   There are no naming conventions that need to be defined for this
   application usage. A subscription to a presence 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.

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.

9. XML Schema

   The following is the XML schema definition of the presence resource list:

   <?xml version="1.0" encoding="UTF-8"?>
   <xs:schema targetNamespace="urn:ietf:params:xml:ns:resource-lists"
     elementFormDefault="qualified" attributeFormDefault="unqualified">
     <xs:element name="presence-lists"> name="resource-lists">
           <xs:element name="list" type="listType" minOccurs="0"
     <xs:complexType name="listType">
       <xs:sequence maxOccurs="unbounded">
           <xs:element name="list" type="listType" minOccurs="0" maxOccurs="unbounded">
                 <xs:extension base="listType"/>
           <xs:element name="external" type="xs:anyURI" minOccurs="0"
           <xs:element name="entry" type="entryType" minOccurs="0"
           <xs:any namespace="##other" processContents="lax"
             minOccurs="0"  maxOccurs="unbounded"/>
       <xs:attribute name="name" type="xs:string" use="required"/>
       <xs:attribute name="uri" type="xs:anyURI" use="optional"/>
       <xs:attribute name="subscribable" name="subscribeable" type="xs:boolean" use="required" /> use="optional"/>
       <xs:anyAttribute namespace="##other"/>
     <xs:complexType name="entryType">
         <xs:element name="display-name" type="display-nameType"/>
         <xs:any namespace="##other" processContents="lax"
            minOccurs="0" maxOccurs="unbounded"/>
       <xs:attribute name="name" type="xs:string" use="required"/>
       <xs:attribute name="uri" type="xs:anyURI" use="optional"/>
     <xs:simpleType name="display-nameType">
       <xs:restriction base="xs:string"/>

10. Example Document

   The following is an example of a document compliant to the schema:

   <?xml version="1.0" encoding="UTF-8"?>
   <resource-lists xmlns:xsi="">
     <list name="friends" uri="" subscribable="true"> subscribeable="true">
       <entry name="Bill" uri="">
         <display-name>Bill Doe</display-name>
       <list name="close-friends" uri=""
         <entry name="Joe" uri="">
           <display-name>Joe Smith</display-name>
         <entry name="Nancy" uri="">
           <display-name>Nancy Gross</display-name>

   TODO: formally validate against schema.

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.

12. IANA Considerations

   There are several IANA considerations associated with this

12.1 XCAP Application Usage ID

   This section registers a new XCAP Application Usage ID (AUID)
   according to the IANA procedures defined in [12]. [7].

      Name of the AUID: presence-lists resource-lists

      Description: A presence resource list application is a usage of the SIP
      events framework (RFC 3265) [9] along with its list extension
      [10], for subscribing any application that
      needs access to a list of presentities (RFC2778) [7]
      stored at resources, identified by a server. URI, to which
      operations, such as subscriptions, can be applied.

12.2 application/presence-lists+xml application/resource-lists+xml MIME Type

      MIME media type name: application

      MIME subtype name: presence-lists+xml 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 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] [11] for
      SIP-based presence [8]. [9].

      Additional Information:

         Magic Number: None
         File Extension: .pl .rl or .xml

         Macintosh file type code: "TEXT"

         Personal and email address for further information: Jonathan

         Intended usage: COMMON

         Author/Change controller: The IETF.

12.3 URN Sub-Namespace Registration for

   This section registers a new XML namespace, as per the guidelines in

      URI: The URI for this namespace is

      Registrant Contact: IETF, SIMPLE working group,
      (, (,
      Jonathan Rosenberg (


                <?xml version="1.0"?>
                <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"
                <html xmlns="">
                  <meta http-equiv="content-type"
                  <title>Resource Lists Namespace</title>
                  <h1>Namespace for Presence Resource Lists</h1>
                  <p>See <a href="[[[URL of published RFC]]]">RFCXXXX</a>.</p>

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

   [7]  Rosenberg, J., "The Extensible Markup Language (XML)
        Configuration Access Protocol  (XCAP)",
        draft-ietf-simple-xcap-00 (work in progress), June 2003.

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.

   [10]  Rosenberg, J.,

   [11]  Roach, A. 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), May October 2003.


   [13]  Rosenberg, J., "The Extensible Markup Language (XML)
         Configuration Access J. and M. Isomaki, "Requirements for Manipulation of
         Data Elements in Session Initiation  Protocol (XCAP)",
         draft-rosenberg-simple-xcap-00 (SIP) for Instant
         Messaging and Presence Leveraging Extensions (SIMPLE) Systems",
         draft-ietf-simple-data-req-03 (work in progress), May June 2003.

Author's Address

   Jonathan Rosenberg
   600 Lanidex Plaza
   Parsippany, NJ  07052

   Phone: +1 973 952-5000

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