BPEL processes are being used to implement both the service and client sides of a...

When acting as the client, a BPEL process may omit the Invoke activity.

When acting as the service, a BPEL process may omit the Reply activity.

When acting as the client, a BPEL processmay not invoke as asynchronous process and wait for a callback.

When acting as the service, a BPEL process may not reply to the client with a well-defined fault message.