By Peter Saint-Andre, IETF Internet Draft
On the Internet today, publication of periodically-updated resources is handled by means of standard technologies such as HTTP, and it is not envisioned that this will change since "The Atom Publishing Protocol"
specifies the use of HTTP for publication. However, existing methods for learning that a resource has been updated are currently limited to "polling" for changes via HTTP, which is inherently inefficient. What is needed is a technology that can be relied on to "push" information only when a resource undergoes a state change, and only to those who are interested in learning about such state changes. This memo describes a method for notifying interested parties about changes in syndicated information encapsulated in the Atom feed format, where such notifications are delivered via an extension to the Extensible Messaging and Presence Protocol (XMPP) for publish-subscribe functionality.
http://xml.coverpages.org/draft-saintandre-atompub-notify-00.txt
See also Atom Publishing Format and Protocol: http://xml.coverpages.org/atom.html