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An application that wants to publish events must obtain a reference to an object that supports an IPublisher interface. An event is published when an IPublisher method implementation is invoked. The implementation of IPublisher must collaborate with an event channel to submit the event. An event channel is an object that supports the IEventChannel interface. The event channel decouples the publisher from the subscriber. When a publisher submits its event, the event channel routes the event to its subscribers by means of an ISubscriber interface. Subscribers are objects that support the ISubscriber interface and are registered to be called by an event channel. Your application design determines how a subscriber is registered. The "Implementation" section of this chapter will explore a few possible alternatives.