Beginning XML, 5th Edition

Chapter 15

SOAP and WSDL

WHAT YOU WILL LEARN IN THIS CHAPTER:

• 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 are
• How to describe a service using WSDL
• The difference between SOAP styles

In Chapter 14 you learned about web services and how they work toward enabling disparate systems to communicate. You can now see that if everyone just chose their own formats in which to send messages back and forth, interoperability would be quite difficult, 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.

In this chapter you take your knowledge of web services 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.

LAYING THE GROUNDWORK

Any web services project requires planning, so before you jump into installing ...