What Is a Web Service?

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So what is a Web service? You probably have some ideas based on the parallels I have drawn with the genesis of the World Wide Web. XML Web services are an open way to perform standards-based remote-procedure calls over standard Internet protocols. Wow ”that's quite a mouthful. I am sure more than one person will argue with that definition because it is difficult to encapsulate the idea of something as large as XML Web services into a single sentence .

So let's examine more closely what a Web service is. XML Web services are not Web pages. They are intended to be created and consumed by applications, not users. Instead of designing the look, you define the schema. The schema is what is important in a Web service.

Several standards apply to XML Web services today. XML Web services communicate over HTTP/1.1, a standard protocol defined in RFC 2616 and RFC 2068. The data that is passed back and forth between XML Web services is encapsulated in XML, which is a W3C recommendation at the present time. Simple Object Access Protocol (SOAP) is an XML grammar that defines the layout of the requests sent to XML Web services and the response received back. As of this writing, SOAP is at W3C NOTE status and more information can be found at http://www.w3.org/TR/SOAP/. Web Services Description Language (WSDL) is another XML grammar for defining the application-specific content of SOAP requests and responses. Universal Description, Discovery, and Integration (UDDI) is a standard protocol for quickly and easily finding XML Web services run by trading and business partners .

Whew! Those are quite a few standards. I also said that XML Web services were open. At their very simplest, XML Web services are a way to take SOAP (XML text) and send it over HTTP. This means that any language that is capable of performing TCP socket operations and string manipulation can play in this space. Granted, if TCP sockets and string manipulation were all you had at your fingertips, it would be like deciding to dig a swimming pool in your backyard with a teaspoon. It would not be trivial, but it would definitely be possible. Fortunately, a number of development platforms, including .NET, are building a significant amount of the infrastructure to make creating and consuming XML Web services trivial.

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