Programming Visual Basic 2005

Chapter 14. Web Services

Normal web pages allow interaction between the client browser and the web server hosting the web page. Many businesses, however, need to provide information not to users, but to other programs.

For example, Amazon.com has a service that allows applications to send in the ISBN of a book and get back information about the publisher, sale price, sales rank, and so forth. This service has no user interface: it is a way for your program to interact with their data. Such a service, providing information with no user interface, using standard web protocols, is called a web service.

Platform Independence

Unlike previous technologies for distributed computing (such as DCOM), web services make it unnecessary for both ends of the connection to be running the same operating system or to be programmed in the same language. For example, the server code might be written in VB.2005 on Windows 2000 while the client is a C++ program running on a Unix machine, or vice versa. In other words, while previous technologies required that the client and server be tightly coupled, web services permit them to be loosely coupled.

All that is necessary is that both server and client support the industry standard protocols HTTP, SOAP, and XML. HTTP is the protocol used by the Web. SOAP (Simple Object Access Protocol) is a lightweight, object-oriented protocol based on XML that, in turn, is a cross-platform standard for formatting and organizing information.