Beginning XML, 4th Edition

Chapter 15. SOAP and WSDL

In the last chapter, you learned about web services and how they work toward enabling disparate systems to communicate. Of course, if everyone just chose their own formats in which to send messages back and forth, that wouldn't do much good in the interoperability area, so a standard format is a must. XML-RPC is good for remote procedure calls, but otherwise limited. SOAP overcomes that problem by enabling rich XML documents to be transferred easily between systems, even allowing for the possibility of attachments. Of course, this flexibility means that you need a way to describe your SOAP messages, and that's where Web Services Description Language (WSDL) comes in. WSDL provides a standard way to describe where and how to make requests to a SOAP-based service.

SOAP originally stood for Simple Object Access Protocol, but as most people found it anything but simple it is now officially a name rather than an acronym, so it doesn't stand for anything.

In this chapter you'll take it a step further by creating a simple web service using a method called REST (covered in the previous chapter). You'll expand your horizons by creating a SOAP service and accessing it via SOAP messages, describing it using WSDL so that other developers can make use of it if desired.

In this chapter you'll learn the following:

• Why SOAP can provide more flexibility than previous RPC protocols

• How to format SOAP messages

• When to use GET versus POST in an HTTP request

• What SOAP intermediaries ...