So far we have talked about operation invocations. A BPEL process explicitly invokes an operation on a service or another BPEL process. Operation invocations are the most common interaction models used in software development. They require that the caller (service consumer) explicitly calls a service (also referred to as a service provider) by invoking a specific operation. This means that we need to know explicitly who we are calling. In cases where we would prefer a more loosely-coupled interaction, without explicitly stating who we are calling, operation invocations would be insufficient. This is where events come in.

An event represents an occurrence, something that happens or is regarded as happening, especially one of some importance. It enables a different interaction model, a model where it is not required to explicitly call a service. Rather, it is sufficient to trigger an event. Once the event is triggered, all services subscribed to this type of event will...