A Web Services Technology Primer

Acronyms abound in the world of Web services. SOAP, WSDL, and Universal Discovery, Description, and Integration ( UDDI) are three key technologies that play a role in building, consuming, and discovering Web services. Let's summarize each of the important technologies:

• Standard Object Access Protocol (SOAP): SOAP is a communications protocol and an XML-based specification for messages. SOAP is the protocol of choice for communicating with Web services, although HTTP-POST and HTTP-GET are viable (but limited) alternatives. SOAP messages are usually transmitted over HTTP, although they may also be transmitted over TCP/IP, SMTP, and assorted other protocols.

• Web Services Description Language (WSDL): WSDL is an XML-based vocabulary that describes the set of SOAP messages that a Web service supports. Every Web service has an associated WSDL file that documents the Web methods , including their arguments and return type. VS .NET uses the WSDL file for generating a proxy class that ASP.NET consumer applications can use for communicating with the Web service. VS .NET also provides a default Service Description screen that summarizes the WSDL information in a readable format. You can view the service description when you navigate directly to a Web service and append the ?WSDL query string to the URL entry.

• Universal Discovery, Description, and Integration (UDDI): UDDI is a registered XML file that publishes information about a Web service in a centralized, browsable location. A UDDI directory enables third parties to locate and research your Web service. For more information, visit http://uddi.microsoft.com .

In this chapter we explore in greater detail the roles of SOAP and WSDL in building and consuming Web services. We also discuss how ASP.NET and VS .NET use these technologies out of the box. Typically, you do not need to alter the WSDL file that ASP.NET generates for your Web service. And usually you do not need to interact with SOAP requests and responses directly. This shielding translates directly into productivity gains as you build Web services. Still, there are times when you will need to do a little work under the hood to optimize your Web service. We spend some time discussing how to work with SOAP extensions for added functionality.