The event processing in FB is the following: there are events that are
fired by different actions happened to the database. The event itself is
fired by the POST_EVENT 'EVENT_NAME' statement. So answering your
question, the event's name is described in the string parameter
following the statement. The event objects don't need any declaration.
On the client side an application must register its interest in a
specified event. The FB event manager maintains a list of applications
that are interested in events and when the event specified by the
application is fired the event manager send an alert to the application.

Regards: Alex