I think forums was the first package to use notifications, so you might take a look at that. The service contract is created in forums/sql/postgresql|oracle/forums-notifications-init.sql and the notifications tcl api is called in forums/tcl/messages-procs.tcl . lars-blogger also plugs into notifications.
Here's a archive.org copy of the original design document:
http://web.archive.org/web/20020625161109/http://dotlrn.openforce.net/doc/notifications.adp
...would be good to have in notifications/www/doc
