Role of Service Description in a Service-Oriented Architecture
Recall the SOA approach, depicted in Figure 6.1. The service provider publishes a service description to one or more service registries. The description of the service is published in service registries, not the actual code for the Web service itself. The service provider uses a service description to tell the service requestor everything it needs to know in order to properly understand how to invoke the Web service.
Similarly, the service description is central to the find operation. The service requestor uses aspects of the service description; for example, you might be looking for a Web service that implements a particular purchase order standard, as the basis for the find query to a service registry. (In Chapter 7, "Discovering Web Services," we discuss service registries at length and describe the find and publish operations in more detail.) The result of the find operation is ultimately a service description made available to the service requestor.
Why does the service provider publish a service description? To communicate to service requestors how to invoke a Web service. Why does a service requestor want to get hold of a service description? Because it describes exactly what needs to happen at the bind operation. Service description is key to the bind operation, describing exactly what message format needs to be delivered to what network address in order to invoke a Web service.