Programming Visual Basic .NET

Chapter 7. Web Services

A web service is a function call over the Internet. Web services are to distributed-application development as components are to desktop-application development. With web services, a component-library developer can expose programmatic functionality over the Internet. The author of a client application can easily use that functionality, even though the client application may exist on a computer on the other side of the world. Furthermore, the client application doesn’t have to be web-based. It can just as easily be a GUI-based application, as long as the computer it’s running on is connected to the Internet.

Web services are not limited to Microsoft products. They are an industrywide movement, with industrywide standardization. Web services running on one vendor’s platform can be used by clients running on entirely different and otherwise incompatible platforms, since they are built on HTTP, XML, and SOAP. These three specifications have extremely broad industry support and are available on virtually all major hardware and operating-system platforms.

HTTP (HyperText Transfer Protocol) is a protocol that was originally developed to allow users to navigate through hypermedia -- documents and other media that link to still other documents and media. This protocol has become the basis for today’s World Wide Web. HTTP has primarily been used to transport documents that are in the form of HTML (HyperText Markup Language), a plain-text document markup language. ...