An Extensible Markup Language (XML) Based Format for Watcher Information
draft-ietf-simple-winfo-format-04

Internet Engineering Task Force                                SIMPLE WG
Internet Draft                                              J. Rosenberg
                                                             dynamicsoft
draft-ietf-simple-winfo-format-04.txt
January 31, 2003
Expires: July 2003

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

STATUS OF THIS MEMO

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   http://www.ietf.org/ietf/1id-abstracts.txt

   To view the list Internet-Draft Shadow Directories, see
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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 XML
   document format for such state.

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                           Table of Contents

   1          Introduction ........................................    3
   2          Terminology .........................................    3
   3          Structure of Watcher Information ....................    3
   4          Computing Watcher Lists from the Document ...........    5
   5          Example .............................................    6
   6          XML Schema ..........................................    7
   7          Security Considerations .............................    9
   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          Contributors ........................................   11
   10         Acknowledgements ....................................   12
   11         Authors Addresses ...................................   12
   12         Normative References ................................   12
   13         Informative References ..............................   13

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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 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

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   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
   this 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
             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 the set of watchers 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 this 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 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].

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        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

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   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 repopulated 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

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   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"/>

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             </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"/>

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             <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 protcol 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:

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             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@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>Watcher Information Namespace</title>
             </head>
             <body>
               <h1>Namespace for Watcher Information</h1>
               <h2>application/watcherinfo+xml</h2>
               <p>See <a href="[[[URL of published RFC]]]">RFCXXXX</a>.</p>
             </body>
             </html>
             END

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9 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
   dynamicsoft
   5100 Tennyson Parkway, Suite 1200
   Plano, Texas 75024
   email: bcampbell@dynamicsoft.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

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   email: bernarda@microsoft.com

   David Gurle
   Microsoft Corporation
   One Microsoft Way
   Redmond, WA 98052-6399
   email: dgurle@microsoft.com

   Jonathan Lennox contributed the text for the DTD and its usage that
   were part of earlier versions of this specification.

10 Acknowledgements

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

11 Authors Addresses

   Jonathan Rosenberg
   dynamicsoft
   72 Eagle Rock Avenue
   East Hanover, NJ 07936
   email: jdrosen@dynamicsoft.com

12 Normative References

   [1] A. B. Roach, "Session initiation protocol (sip)-specific event
   notification," RFC 3265, Internet Engineering Task Force, June 2002.

   [2] J. Rosenberg, "A watcher information event template-package for
   the session initiation protocol (SIP)," internet draft, Internet
   Engineering Task Force, Dec. 2002.  Work in progress.

   [3] S. Bradner, "Key words for use in rfcs to indicate requirement
   levels," RFC 2119, Internet Engineering Task Force, Mar. 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/.

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   [5] R. Moats, "URN syntax," RFC 2141, Internet Engineering Task
   Force, May 1997.

   [6] R. Moats, "A URN namespace for IETF documents," RFC 2648,
   Internet Engineering Task Force, Aug. 1999.

   [7] M. Mealling, "The IETF XML registry," internet draft, Internet
   Engineering Task Force, July 2002.  Work in progress.

   [8] J. Rosenberg, H. Schulzrinne, G. Camarillo, A. R. Johnston, J.
   Peterson, R. Sparks, M. Handley, and E. Schooler, "SIP: session
   initiation protocol," RFC 3261, Internet Engineering Task Force, June
   2002.

   [9] M. Murata, S. S. Laurent, and D. Kohn, "XML media types," RFC
   3023, Internet Engineering Task Force, Jan. 2001.

   [10] J. Rosenberg, "A presence event package for the session
   initiation protocol (SIP)," internet draft, Internet Engineering Task
   Force, Dec. 2002.  Work in progress.

13 Informative References

   [11] M. Day, J. Rosenberg, and H. Sugano, "A model for presence and
   instant messaging," RFC 2778, Internet Engineering Task Force, Feb.
   2000.

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   Director.

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