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Web Services

In the past two years, Web services have become a hot topic. Thanks to Microsoft’s .NET initiative,

developers are now able to create, deploy, and access Web services quickly and easily. The idea is

simple: Servers can provide (

publish

) Web services over the Internet. Any developer can access this

functionality from a program, seamlessly providing the functionality encapsulated by the Web ser-

vice. But Web services aren’t available only to compiled programs; they are also available to Web

pages using JavaScript.

A Quick Web Service Primer

Understanding what Web services are is the key to understanding how to use them. This section

covers some of the basics.

What is a Web service?

Think of a Web service as a function call, only this function exists on a server while being called

from the client. This necessitates that messages be sent back and forth between the client (called

the consumer) and the server. These messages are in a format called SOAP (Simple Object Access

Protocol), which is an XML-based wrapper for Web service messages. The SOAP message is trans-

ferred using a standard HTTP request (although other protocols can be used as well) with a couple

of special request headers:

SOAPAction

— Gives a specific SOAP action to take if there are multiple possible actions.

If only one action is possible, this is typically left as an empty string.

Content-Type

— Set to text/xml

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