微软的文章:what are xml web services

XML Web services allow applications to communicate regardless of operating system or programming language via the Internet. They can be implemented on any platform and are defined through public standards organizations such as the W3C. And with XML Web services, not only can applications share data, but they can also invoke capabilities from other applications without regard to how other applications were built. Sharing data through XML allows them to be independent of each other while simultaneously giving them the ability to loosely link themselves into a collaborating group that performs a particular task.

Web sites are about presenting information to a user: they are the communication vehicle for servers to talk to users. XML Web services, on the other hand, offer a direct means for applications to interact with other applications. Applications hosted internally, as well as on remote systems, can communicate via the Internet by using XML and SOAP messages.