[standards-jig] JEP-0060 PubSub: We need privacy lists in PubSub

Bob Wyman bob at wyman.us
Tue Feb 18 16:52:50 UTC 2003

> If you subscribe to someone's presence you say:
> I want to receive this bit of information.
	A different wording, with equivelant meaning would be: "I
subscribe to all published updates to this topic or node." i.e. What is
called, in the academic literature, a "topic-based" PubSub system.

> If you want more finegrained control of what 
> notifications reach you, you might want to implement 
> a filtering pubsub proxy component.
	If the server uses information other than the topic or node in
the published information to decide who to send updates to, what you
have is a "content-based" system. In such a system, decisions are made
based on topic plus content, not topic alone. 
	Privacy Lists, (either white-lists or black-lists) convert a
topic-based system to content-based.

	Presence systems are usually thought of as though each publisher
was a distinct topic or node. An alternative view of the same systems is
to say that the presence server is the thing to which you subscribe and
the specification of the particular publisher is, effectively a very
simple content-based subscription.
	I don't believe it possible to come up with any particularly
interesting architectural distinctions between what is typical in
presence systems and what is covered by PubSub systems as discussed in
the literature. PubSub is a fundamental pattern of computer science and
Presence is just one implementation of the pattern. Given this, it
doesn't seem to make sense to me to have distinct protocols for presence
and for PubSub. 

		bob wyman

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