[standards-jig] Pub/Sub Explanation

Robert Norris rob at cataclysm.cx
Tue Apr 16 23:00:23 UTC 2002


> by Gamma et al., which rubs me the wrong way). In the Observer Pattern,
> a dependent (or "subject") is notified of changes to an object. This is
> straight notification, and a service that informs multiple subjects of 
> changes to one object could be thought of as an event notification relay.

This is _exactly_ what JEP 21 is. The example I use throughout, of the
IMAP store sending event notifications, is a perfect example of this.
The notifications say "something happened", not (necessarily) "here's
some data for you".

> With pure event notification, it is the responsibility of the subject to
> poll for the content of the change. We might also have more of a push
> model for certain kinds of content, or a hybrid model. To me, whether
> we have pure pull, pure push, or hybrid depends on what kind of data
> is being published. Think of a simple pub/sub system for weblogs. I

Agreed. What if I'm not interested in the data associated with this
particular event? Why should I have it forced on me? (though I realise
that is appropriate in some applications).

Rob.

-- 
Robert Norris                                       GPG: 1024D/FC18E6C2
Email+Jabber: rob at cataclysm.cx                Web: http://cataclysm.cx/
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