|
|
To make a Web service useful, a service consumer who has discovered a set of useful services must be able to determine
How to invoke the service.
What is the service interface; that is, what are its methods, method signatures, and return values?
Is one service more secure than the others?
How can services be combined to create a macro service (often referred to as service orchestration)?
Although these three forms of description provide complete information regarding a service, a consumer may not require all three every time the service is used. It is quite probable, for example, that a consumer invoking a standalone service is uninterested in how the service is to be orchestrated or combined with other services. Also, where only one provider exists for a service, the nonfunctional characteristics (response performance, scalability, etc.), although important, may serve no useful purpose.
 |
Only the first form of description, the functional (the "how to invoke") is always required before a service can be invoked. In this chapter, the focus is on explaining the most common, accepted form for functional description of Web services: WSDL. The WSDL specification is a submission to the World Wide Web Consortium (W3C) that addresses the first of these three forms and is the focus of this chapter. The latter two forms are discussed in s 6 and 7, respectively.
|
|
|