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

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
   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:

      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:

   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.

   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
   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"

                    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"/>
                <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.

   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>

       </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.

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
   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

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.

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