Personal Pubsub

The Jabber community just came up with a very elegant way to give IM users their own multi content news (aka publish/subscribe) service: JEP-0163 Traditional IM use of a personal pubsub service include avatar distribution, music or mood sharing. Yet the possibilities are limitless: one could use this mechanism to share all kinds of domain-specific information. XMPP-enabled Call Center systems could allow agents to selectively share with others information about current calls, questions they are not able to answer, etc... XMPP-enabled blog sites can notify your buddies of your new posts.

This mechanism is also really good for bots. Without it, the only client-independent ways a bot has to communicate with you is the presence status (show and status), or vanilla messages (natural language in subject and body) to individual folks. You can still make extensions for controlled environments, but this does not solve the issue of overloading presence and having the bot keep track of who to send what to.

The protocol is based on the rich (but complex) XMPP publish/subscribe protocol, with some simplifications taking into account the fact that we are talking specifically about persons. But what is really interesting about the proposal is how it leverages presence subscriptions and entity capabilities to become really simple in the very common case where events are shared with your buddies. It's like this: By virtue of subscribing to someone's presence, and advertizing the capability to handle a specific type of content, you are implicitely subscribed to content of this type published by this person. In other words, just by sharing one capability (one xml element in a previously shared presence stanza), you are automatically subscribed to all of your buddy's content corresponding to this capability. Can this get easier or more efficient? I doubt it. A very nice way to build on existing protocols.