Web Services Demystified

Web services: they're the latest buzzword on the block. If you believe what you read in the glossy trade press, not to mention Microsoft's $200 million .NET advertising campaign, Web services are (in no particular order):

• Your new best friend
• The saviour of your business
• The doom of your business
• The next generation of the World Wide Web

None of this really tells you how they work or what they do for you, though. To make matters worse, Web services come with a plethora of snappy acronyms that don't mean a whole heck of a lot at first glance either:

• SOAP: Simple Object Access Protocol
• WSDL: Web Service Description Language
• UDDI: Universal Description, Discovery, and Integration
• XML: Extensible Markup Language

...and those are just the most important ones!

Web service technology is a lot like the Wizard of Oz. Everyone will tell you it's important and great, but no one can tell you exactly why. In this article, I'll throw back the curtains and show you the man pulling the levers. This should enable you to decide how Web services figure into your future as a Web developer, if indeed they should interest you at all!

What Are Web Services, Really?

Okay, let me start with a straight answer: a Web service is a network interface to application functionality, based on standard Internet technologies (see Fig. 1).

Fig. 1: A Web service lets you access application functionality over the Internet

Let's say that a program on your computer (the Client Program in Fig. 1) needs spell checking functionality. Instead of doing the spell check itself, however, it might make use of a Web service to do so. Whenever it needed to perform a spell check, the program would send a request to a Web service to do it. The Web service would do the spell check, and respond with the results. From a programming standpoint, Web services can be thought of as functions that you can call over the Internet.

The neat thing about Web services is that they're based on standard protocols that serve to ensure that any Web service can be accessed by any client program, no matter what language they're written in and no matter what platform they're running on. So a Java program can access and use a Web service written in VB.NET and deployed on a Windows server just as easily as a Windows program can use a Web service written in Java and running on a Linux Web server.

Because of this flexibility, several companies could produce competing spell checking Web services, and you could sign up for any one of them for your program to use. As long as they all support the same interface, the program can use any of them interchangeably. Perhaps different services might check different languages!

Although a bustling market for spell checking Web services won't erupt overnight, some areas where Web services are expected to spread quickly include stock quotes, currency exchange rates, and inventory searches. But don't let those expectations limit your imagination!