RFC 3858 (rfc3858) - Page 2 of 13
An Extensible Markup Language (XML) Based Format for Watcher Information
Alternative Format: Original Text Document
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