Introductory text: NotificationProducer role

[David Hull <dmh@tibco.com>]

In the draft I sent out, I have:

This specification defines a role called the NotificationProducer. A NotificationProducer accepts incoming Subscribe requests from a Subscriber.Each subscribe request identifies one or more Topics of interest and a reference to a NotificationConsumer, which may or may not be the Subscriber. The NotificationProducer is responsible for ensuring that the Notifications addressed by the given Topics are delivered to the requested NotificationConsumer.  It may do this either directly or by delegating to an existing message delivery system, a system of NotificationBrokers, or some other mechanism.