An event is triggered in Message Control through which a Workflow can be started. For more information see Using Events.

Choose Communication in the condition record and enter the object type, for which the event should be triggered, as well as the event itself. The object type must be assigned your application, the event on the other hand the object type. The "correct" workflows are specified and started from the object type and event as event receivers.

As with all transmission media you need a processing program. The program must generate the event. At the same time, it can call the function module SAP_WAPI_CREATE_EVENT.