Web Services Essentials

Chapter 6. WSDL Essentials

WSDL is a specification defining how to describe web services in a common XML grammar. WSDL describes four critical pieces of data:

• Interface information describing all publicly available functions

• Data type information for all message requests and message responses

• Binding information about the transport protocol to be used

• Address information for locating the specified service

In a nutshell, WSDL represents a contract between the service requestor and the service provider, in much the same way that a Java interface represents a contract between client code and the actual Java object. The crucial difference is that WSDL is platform- and language-independent and is used primarily (although not exclusively) to describe SOAP services.

Using WSDL, a client can locate a web service and invoke any of its publicly available functions. With WSDL-aware tools, you can also automate this process, enabling applications to easily integrate new services with little or no manual code. WSDL therefore represents a cornerstone of the web service architecture, because it provides a common language for describing services and a platform for automatically integrating those services.

This chapter covers all aspects of WSDL, including the following topics:

• An overview of the WSDL specification, complete with detailed explanations of the major WSDL elements

• Two basic WSDL examples to get you started

• A brief survey of WSDL invocation tools, including the IBM Web Services Invocation ...