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rfc:rfc3858

Network Working Group J. Rosenberg Request for Comments: 3858 dynamicsoft Category: Standards Track August 2004

    An Extensible Markup Language (XML) Based Format for Watcher
                            Information

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 (2004).

Abstract

 Watchers are defined as entities that request (i.e., subscribe to)
 information about a resource.  There is fairly complex state
 associated with these subscriptions.  The union of the state for all
 subscriptions to a particular resource is called the watcher
 information for that resource.  This state is dynamic, changing as
 subscribers come and go.  As a result, it is possible, and indeed
 useful, to subscribe to the watcher information for a particular
 resource.  In order to enable this, a format is needed to describe
 the state of watchers on a resource.  This specification describes an
 Extensible Markup Language (XML) document format for such state.

Table of Contents

 1.  Introduction ................................................   2
 2.  Terminology ...............................................     2
 3.  Structure of Watcher Information ...........................    2
 4.  Computing Watcher Lists from the Document ..................    5
 5.  Example ....................................................    6
 6.  XML Schema .................................................    6
 7.  Security Considerations ....................................    8
 8.  IANA Considerations ........................................    9
     8.1. application/watcherinfo+xml MIME Registration .........    9
     8.2. URN Sub-Namespace Registration for
          urn:ietf:params:xml:ns:watcherinfo ....................   10
 9.  Normative References .......................................   10
 10. Informative References .....................................   11

Rosenberg Standards Track [Page 1] RFC 3858 Watcher Info August 2004

 11. Acknowledgements ...........................................   11
 12. Contributors ...............................................   12
 13. Author's Address ...........................................   13
 14. Full Copyright Statement ...................................   14

1. Introduction

 Watchers are defined as entities that request (i.e., subscribe to)
 information about a resource, using the SIP event framework, RFC 3265
 [1].  There is fairly complex state associated with these
 subscriptions.  This state includes the identity of the subscriber,
 the state of the subscription, and so on.  The union of the state for
 all subscriptions to a particular resource is called the watcher
 information for that resource.  This state is dynamic, changing as
 subscribers come and go.  As a result, it is possible, and indeed
 useful, to subscribe to the watcher information for a particular
 resource.  An important application of this is the ability for a user
 to find out the set of subscribers to their presentity [11].  This
 would allow the user to provide an authorization decision for the
 subscription.
 To support subscriptions to watcher information, two components are
 needed.  The first is the definition of a SIP event template-package
 for watcher information.  The other is the definition of a data
 format to represent watcher information.  The former is specified in
 [2], and the latter is specified here.

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 BCP 14, RFC 2119
 [3] and indicate requirement levels for compliant implementations.
 This document also uses the terms subscriber, watcher, subscription,
 notification, watcherinfo subscription, watcherinfo subscriber, and
 watcherinfo notification with the meanings described in [2].

3. Structure of Watcher Information

 Watcher information is an XML document [4] that MUST be well-formed
 and SHOULD be valid.  Watcher information documents MUST be based on
 XML 1.0 and MUST be encoded using UTF-8.  This specification makes
 use of XML namespaces for identifying watcherinfo documents and
 document fragments.  The namespace URI for elements defined by this
 specification is a URN [5], using the namespace identifier 'ietf'
 defined by [6] and extended by [7].  This URN is:

Rosenberg Standards Track [Page 2] RFC 3858 Watcher Info August 2004

    urn:ietf:params:xml:ns:watcherinfo
 A watcher information document begins with the root element tag
 "watcherinfo".  It consists of any number of "watcher-list" sub-
 elements, each of which is a list of watchers for a particular
 resource.  Other elements from different namespaces MAY be present
 for the purposes of extensibility; elements or attributes from
 unknown namespaces MUST be ignored.  There are two attributes
 associated with the "watcherinfo" element, both of which MUST be
 present:
 version: This attribute allows the recipient of watcherinfo documents
    to properly order them.  Versions start at 0, and increment by one
    for each new document sent to a watcherinfo subscriber.  Versions
    are scoped within a watcherinfo subscription.  Versions MUST be
    representable using a 32 bit integer.  However, versions do not
    wrap.
 state: This attribute indicates whether the document contains
    the full watcherinfo state, or whether it contains only
    information on those watchers which have changed since the
    previous document (partial).
 Each "watcher-list" element contains a list of "watcher" elements,
 each of which describes a watcher on a particular resource.  Other
 elements from different namespaces MAY be present for the purposes of
 extensibility; elements or attributes from unknown namespaces MUST be
 ignored.  There are two attributes associated with the "watcher-list"
 element, both of which MUST be present:
 resource: This attribute contains a URI for the resource being
    watched by that list of watchers.  It is mandatory.
 package: This attribute contains a token indicating the event
    package for which watcher information on that resource is being
    provided.  It is mandatory.
 The "watcher" element describes a watcher in the watcher list.  The
 value of the "watcher" element is a URI for the watcher.  This URI
 SHOULD be the authenticated identity of the watcher as determined by
 the server processing the subscription.  As such, this URI will
 usually be an address-of-record (for example, sip:joe@example.com) as
 opposed to a device address (for example, sip:joe@192.0.2.3).  There
 are three mandatory attributes which MUST be present:

Rosenberg Standards Track [Page 3] RFC 3858 Watcher Info August 2004

 id: A unique identifier for the subscription described by the
    watcher element.  The id MUST be representable using the grammar
    for token as specified by RFC 3261 [8].  It MUST be unique across
    all other watchers reported in documents sent in notifications for
    a particular watcherinfo subscription.
 status: The status of the subscription.  The meaning of the
    various statuses are defined in the watcher information event
    package [2].
 event: The event which caused the transition to the current
    status.  The events are defined in the watcher information event
    package [2].
 There are also some optional, informative attributes of the watcher
 element.  These are:
 display-name: A textual representation of the name of the
    subscriber.
 expiration: The amount of time, in seconds from the current
    time, that the subscription will expire.
 duration-subscribed: The amount of time, expressed in seconds,
    between the time the SUBSCRIBE which created the subscription was
    received, and the current time.
 The xml:lang attribute MAY be used with the "watcher" element to
 specify the language of the "display-name".
 The number of watchers present for each resource, and the set of
 resources listed, depends on the type of data being provided, and to
 whom.
 For example, consider a presence system using watcher information. In
 one scenario, a user, A, subscribes to the presence of another user,
 B.  A would like to find out about the status of their subscription.
 To do so, A subscribes to the watcher information for B's presence.
 A does not have authorization to learn the status of all watchers for
 B's presence.  As a result, the watcher information sent to A will
 contain only one watcher - A themself.
 In another scenario, a user, B, wishes to learn the set of people who
 have subscribed to B's presence.  To do this, B subscribes to the
 watcher information for B's presence.  Here, B is authorized to see
 all the watchers of B's presence.  As a result, the watcher
 information sent to B will contain all watchers of B's presence.

Rosenberg Standards Track [Page 4] RFC 3858 Watcher Info August 2004

 In the case where an administrator wishes to learn the current status
 in the system, the watcher information could contain all watchers for
 all resources.

4. Computing Watcher Lists from the Document

 Typically, the watcherinfo NOTIFY will only contain information about
 those watchers whose state has changed.  To construct a coherent view
 of the total state of all watchers, a watcherinfo subscriber will
 need to combine NOTIFYs received over time.  The watcherinfo
 subscriber maintains a table for each watcher list it receives
 information about.  Each watcher list is uniquely identified by the
 URI in the "resource" attribute of the "watcher-list" element.  Each
 table contains a row for each watcher in that watcher list.  Each row
 is indexed by the unique ID for that watcher.  It is conveyed in the
 "id" attribute of the "watcher" element.  The contents of each row
 contain the state of that watcher as conveyed in the "watcher"
 element.  The tables are also associated with a version number.  The
 version number MUST be initialized with the value of the "version"
 attribute from the "watcherinfo" element in the first document
 received.  Each time a new document is received, the value of the
 local version number, and the "version" attribute in the new
 document, are compared.  If the value in the new document is one
 higher than the local version number, the local version number is
 increased by one, and the document is processed.  If the value in the
 document is more than one higher than the local version number, the
 local version number is set to the value in the new document, the
 document is processed, and the watcherinfo subscriber SHOULD generate
 a refresh request to trigger a full state notification.  If the value
 in the document is less than the local version, the document is
 discarded without processing.
 The processing of the watcherinfo document depends on whether it
 contains full or partial state.  If it contains full state, indicated
 by the value of the "state" attribute in the "watcherinfo" element,
 the contents of all tables associated with this watcherinfo
 subscription are flushed.  They are re-populated from the document.
 A new table is created for each "watcher-list" element, and a new row
 in each table is created for each "watcher" element.  If the
 watcherinfo contains partial state, as indicated by the value of the
 "state" attribute in the "watcherinfo" element, the document is used
 to update the existing tables.  For each "watcher-list" element, the
 watcherinfo subscriber checks to see if a table exists for that list.
 This check is done by comparing the URI in the "resource" attribute
 of the "watcher-list" element with the URI associated with the table.
 If a table doesn't exist for that list, one is created.  For each
 "watcher" element in the list, the watcherinfo subscriber checks to
 see whether a row exists for that watcher.  This check is done by

Rosenberg Standards Track [Page 5] RFC 3858 Watcher Info August 2004

 comparing the ID in the "id" attribute of the "watcher" element with
 the ID associated with the row.  If the watcher doesn't exist in the
 table, a row is added, and its state is set to the information from
 that "watcher" element.  If the watcher does exist, its state is
 updated to be the information from that "watcher" element.  If a row
 is updated or created, such that its state is now terminated, that
 entry MAY be removed from the table at any time.

5. Example

 The following is an example of watcher information for a presentity,
 who is a professor.  There are two watchers, userA and userB.

<?xml version="1.0"?> <watcherinfo xmlns="urn:ietf:params:xml:ns:watcherinfo"

           version="0" state="full">
<watcher-list resource="sip:professor@example.net" package="presence">
  <watcher status="active"
           id="8ajksjda7s"
           duration-subscribed="509"
           event="approved" >sip:userA@example.net</watcher>
  <watcher status="pending"
           id="hh8juja87s997-ass7"
           display-name="Mr. Subscriber"
           event="subscribe">sip:userB@example.org</watcher>
</watcher-list>

</watcherinfo>

6. XML Schema

 The following is the schema definition of the watcherinfo document
 format:

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"

     targetNamespace="urn:ietf:params:xml:ns:watcherinfo"
     xmlns:tns="urn:ietf:params:xml:ns:watcherinfo" >

<!– This import brings in the XML language attribute xml:lang–>

<xs:import namespace="http://www.w3.org/XML/1998/namespace"
           schemaLocation="http://www.w3.org/2001/03/xml.xsd" />
<xs:element name="watcherinfo">
  <xs:complexType>
    <xs:sequence>
      <xs:element ref="tns:watcher-list" minOccurs="0"
                  maxOccurs="unbounded"/>
      <xs:any namespace="##other" processContents="lax" minOccurs="0"
              maxOccurs="unbounded"/>
    </xs:sequence>
    <xs:attribute name="version" type="xs:nonNegativeInteger"

Rosenberg Standards Track [Page 6] RFC 3858 Watcher Info August 2004

                  use="required"/>
    <xs:attribute name="state" use="required">
      <xs:simpleType>
        <xs:restriction base="xs:string">
          <xs:enumeration value="full"/>
          <xs:enumeration value="partial"/>
        </xs:restriction>
      </xs:simpleType>
    </xs:attribute>
  </xs:complexType>
</xs:element>
<xs:element name="watcher-list">
  <xs:complexType>
    <xs:sequence>
      <xs:element ref="tns:watcher" minOccurs="0" maxOccurs=
       "unbounded"/>
        <xs:any namespace="##other" processContents="lax"
                minOccurs="0" maxOccurs="unbounded"/>
    </xs:sequence>
    <xs:attribute name="resource" type="xs:anyURI" use="required"/>
    <xs:attribute name="package" type="xs:string" use="required"/>
  </xs:complexType>
</xs:element>
<xs:element name="watcher">
  <xs:complexType>
    <xs:simpleContent>
      <xs:extension base="xs:anyURI">
        <xs:attribute name="display-name" type="xs:string"/>
        <xs:attribute name="status" use="required">
          <xs:simpleType>
            <xs:restriction base="xs:string">
              <xs:enumeration value="pending"/>
              <xs:enumeration value="active"/>
              <xs:enumeration value="waiting"/>
              <xs:enumeration value="terminated"/>
            </xs:restriction>
          </xs:simpleType>
        </xs:attribute>
        <xs:attribute name="event" use="required">
          <xs:simpleType>
            <xs:restriction base="xs:string">
              <xs:enumeration value="subscribe"/>
              <xs:enumeration value="approved"/>
              <xs:enumeration value="deactivated"/>
              <xs:enumeration value="probation"/>
              <xs:enumeration value="rejected"/>
              <xs:enumeration value="timeout"/>
              <xs:enumeration value="giveup"/>

Rosenberg Standards Track [Page 7] RFC 3858 Watcher Info August 2004

              <xs:enumeration value="noresource"/>
            </xs:restriction>
          </xs:simpleType>
        </xs:attribute>
        <xs:attribute name="expiration" type="xs:unsignedLong"/>
        <xs:attribute name="id" type="xs:string" use="required"/>
        <xs:attribute name="duration-subscribed"
            type="xs:unsignedLong"/>
        <xs:attribute ref="xml:lang"/>
      </xs:extension>
    </xs:simpleContent>
  </xs:complexType>
</xs:element>

</xs:schema>

7. Security Considerations

 Watcher information is sensitive information.  The protocol used to
 distribute it SHOULD ensure privacy, message integrity, and
 authentication.  Furthermore, the protocol should provide access
 controls which restrict who can see who elses watcher information.

8. IANA Considerations

 This document registers a new MIME type, application/watcherinfo+xml,
 and registers a new XML namespace.

8.1. application/watcherinfo+xml MIME Registration

 MIME media type name: application
 MIME subtype name: watcherinfo+xml
 Mandatory parameters: none
 Optional parameters: Same as charset parameter application/xml
      as specified in RFC 3023 [9].
 Encoding considerations: Same as encoding considerations of
      application/xml as specified in RFC 3023 [9].
 Security considerations: See Section 10 of RFC 3023 [9] and
      Section 7 of this specification.
 Interoperability considerations: none.
 Published specification: This document.

Rosenberg Standards Track [Page 8] RFC 3858 Watcher Info August 2004

 Applications which use this media type: This document type has
      been used to support subscriber authorization functions for
      SIP-based presence [10] [2].
 Additional Information:
      Magic Number: None
      File Extension: .wif 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.

8.2. URN Sub-Namespace Registration for

   urn:ietf:params:xml:ns:watcherinfo
 This section registers a new XML namespace, as per the guidelines in
 [7].
 URI: The URI for this namespace is
      urn:ietf:params:xml:ns:watcherinfo.
 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>Watcher Information Namespace</title>
     </head>
     <body>
       <h1>Namespace for Watcher Information</h1>
       <h2>urn:ietf:params:xml:ns:watcherinfo</h2>
       <p>See <a href="ftp://ftp.rfc-editor.org/in-notes/rfc3858.txt">
          RFC3858</a>.</p>

Rosenberg Standards Track [Page 9] RFC 3858 Watcher Info August 2004

     </body>
     </html>
     END

9. Normative References

 [1]  Roach, A. B., "Session Initiation Protocol (SIP)-Specific Event
      Notification", RFC 3265, June 2002.
 [2]  Rosenberg, J., "A Watcher Information Event Template-Package for
      the Session Initiation Protocol (SIP)", RFC 3857, August 2004.
 [3]  Bradner, S., "Key Words for Use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997.
 [4]  T. Bray, J. Paoli, and C. M. Sperberg-McQueen, "Extensible
      Markup language (XML) 1.0 (second edition)," W3C Recommendation
      REC-xml-20001006, World Wide Web Consortium (W3C), Oct. 2000.
      Available at http://www.w3.org/XML/.
 [5]  Moats, R., "URN Syntax", RFC 2141, May 1997.
 [6]  Moats, R., "A URN Namespace for IETF Documents", RFC 2648,
      August 1999.
 [7]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, January
      2004.
 [8]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
      Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
      Session Initiation Protocol", RFC 3261, June 2002.
 [9]  Murata, M., Laurent, S., and D. Kohn, "XML Media Types", RFC
      3023, January 2001.
 [10] Rosenberg, J., "A Presence Event Package for the Session
      Initiation Protocol (SIP)", RFC 3856, August 2004.

10. Informative References

 [11] Day, M., Rosenberg, J., and H. Sugano, "A Model for Presence and
      Instant Messaging", RFC 2778, February 2000.

11. Acknowledgements

 The authors would like to thank Sean Olson, Steve Donovan, and Cullen
 Jennings for their detailed comments and assistance with the XML
 schema.

Rosenberg Standards Track [Page 10] RFC 3858 Watcher Info August 2004

12. Contributors

 The following people were part of the original design team that
 developed the first version of this specification:
 Dean Willis
 dynamicsoft
 5100 Tennyson Parkway, Suite 1200
 Plano, Texas 75024
 EMail: dwillis@dynamicsoft.com
 Robert Sparks
 dynamicsoft
 5100 Tennyson Parkway, Suite 1200
 Plano, Texas 75024
 EMail: rsparks@dynamicsoft.com
 Ben Campbell
 EMail: ben@nostrum.com
 Henning Schulzrinne
 Columbia University
 M/S 0401
 1214 Amsterdam Ave.
 New York, NY 10027-7003
 EMail: schulzrinne@cs.columbia.edu
 Jonathan Lennox
 Columbia University
 M/S 0401
 1214 Amsterdam Ave.
 New York, NY 10027-7003
 EMail: lennox@cs.columbia.edu
 Christian Huitema
 Microsoft Corporation
 One Microsoft Way
 Redmond, WA 98052-6399
 EMail: huitema@microsoft.com

Rosenberg Standards Track [Page 11] RFC 3858 Watcher Info August 2004

 Bernard Aboba
 Microsoft Corporation
 One Microsoft Way
 Redmond, WA 98052-6399
 EMail: bernarda@microsoft.com
 David Gurle
 Reuters Corporation
 EMail: David.Gurle@reuters.com
 Jonathan Lennox contributed the text for the DTD and its usage that
 were part of earlier versions of this specification.

13. Author's Address

 Jonathan Rosenberg
 dynamicsoft
 600 Lanidex Plaza
 Parsippany, NJ 07054
 EMail: jdrosen@dynamicsoft.com

Rosenberg Standards Track [Page 12] RFC 3858 Watcher Info August 2004

14. Full Copyright Statement

 Copyright (C) The Internet Society (2004).  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 currently provided by the
 Internet Society.

Rosenberg Standards Track [Page 13]

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