Software Architect's Handbook

The mediator topology

A mediator topology for EDAs uses a single event queue and an event mediator to route events to the relevant event processors. This topology is commonly used when multiple steps are required to process an event.

With the mediator topology, event producers send events into an event queue. There can be many event queues in an EDA. Event queues are responsible for sending event messages on to the event mediator. All of these events, referred to as initial events, go through an event mediator. The event mediator then performs any necessary orchestration:

After the event mediator orchestrates each event from the event queue, ...