Chapter 36: Web Services with ASP.NET

Overview

Web services are a way of performing remote method calls over HTTP that can make use of Simple Object Access Protocol (SOAP). In the past, this issue was fraught with difficulty, as anyone who has any DCOM (Distributed COM) experience knows. The act of instantiating an object on a remote server, calling a method, and obtaining the result was far from simple, and the necessary configuration was even trickier.

SOAP simplifies matters immensely. This technology is an XML-based standard that details how method calls can be made over HTTP in a reproducible manner. A remote SOAP server is capable of understanding these calls and performing all the hard work for you, such as instantiating the required object, making the call, and returning a SOAP-formatted response to the client.

The .NET Framework makes it very easy for you to use of all this. As with ASP.NET, you are able to use the full array of C# and .NET techniques on the server, but (perhaps more importantly) the simple consumption of Web services can be achieved from any platform with HTTP access to the server. In other words, it is conceivable that Linux code could, for example, use ASP.NET Web services, or even Internet-enabled fridges. To quote a real-world example, in the past I have had great success combining ASP.NET Web services with Macromedia Flash to create data-enabled flash content.

In addition, Web services can be completely described using Web Service Description Language (WSDL), allowing the dynamic discovery of Web services at runtime. WSDL provides descriptions of all methods (along with the types required to call them) using XML with XML schemas. A wide variety of types are available to Web services, which range from simple primitive types to full DataSet objects; this makes it possible to marshal full in-memory databases to a client. This can result in a dramatic reduction in load on a database server.

In this chapter, you will do the following:

• Look at the syntax of SOAP and WSDL, then move on to see how they are used by Web services.

• Learn how to expose and consume Web services.

• Work through a complete example building on the meeting room booking application from Chapter 32, “ASP.NET Pages,” and Chapter 33, “ASP.NET Development,” to illustrate the use of Web services.

• Learn how to exchange data using SOAP Headers.