An Extensible Markup Language (XML) Based Format for Watcher Information
RFC 3858

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