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Network Working Group                                       J. RosenbergRequest for Comments: 3858                                   dynamicsoftCategory: Standards Track                                    August 2004An Extensible Markup Language (XML) Based Format for WatcherInformationStatus 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 Contents1.  Introduction ................................................22.  Terminology ...............................................23.  Structure of Watcher Information ...........................24.  Computing Watcher Lists from the Document ..................55.  Example ....................................................66.  XML Schema .................................................67.  Security Considerations ....................................88.  IANA Considerations ........................................98.1. application/watcherinfo+xml MIME Registration .........9       8.2. URN Sub-Namespace Registration for            urn:ietf:params:xml:ns:watcherinfo ....................109.  Normative References .......................................1010. Informative References .....................................11Rosenberg                   Standards Track                     [Page 1]

RFC 3858                      Watcher Info                   August 200411. Acknowledgements ...........................................1112. Contributors ...............................................1213. Author's Address ...........................................1314. Full Copyright Statement ...................................141. 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 inBCP 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 byRFC 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 byRosenberg                   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"                         duration-subscribed="509"             event="approved" >sip:userA@example.net</watcher>    <watcher status="pending"                         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 inRFC 3023 [9].   Encoding considerations: Same as encoding considerations of        application/xml as specified inRFC 3023 [9].   Security considerations: SeeSection 10 of RFC 3023 [9] andSection 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>       END9.  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 athttp://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",RFC3023, 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 200412.  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.comRosenberg                   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.comRosenberg                   Standards Track                    [Page 12]

RFC 3858                      Watcher Info                   August 200414.  Full Copyright Statement   Copyright (C) The Internet Society (2004).  This document is subject   to the rights, licenses and restrictions contained inBCP 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 inBCP 78 andBCP 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 athttp://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]