In Chapter 7, “Understanding SOAP,” you learned the basics of Simple Object Access Protocol (SOAP), a simple XML-based protocol for RPC (Remote Procedure Call). In Chapter 8, “SOAP Basics,” you learned how to develop SOAP Web services with Apache SOAP. In Chapter 11, you learned about WSDL (Web Services Definition Language).
SOAP defines a simple and elegant protocol to implement remote procedure calls over HTTP with XML. SOAP also supports XML message passing, which is covered in Chapter 15, “JAXM.” but this chapter concentrates on RPCs only.
WSDL is an XML vocabulary to describe Web services: which services are available, over which transport, what are the expected parameters, or return values, and more.