Services can be invoked in several ways.
• A one-way operation is executed once and does not wait for a response.
• A request-response operation is executed once and waits for one response. In a
request-response service, communication flows in both directions. The complete
interaction consists of two point-to-point messages—a request and a response. The
interaction is only considered complete after the response has arrived.
• Publication (notification) means an operation sends information on an as-needed
basis, potentially multiple times.
• Subscription means incoming information is processed on an as-needed basis,
potentially multiple times.