" An application using a Web service (a client application) can invoke it and pass data to and from it very easily, because all communication between them is in the form of XML files sent using a standard protocol such as HTTP. This means the client application has no need to know details of how the component is deployed, what language it is in, and so on.

In theory, exposing a component as a Web service means it can be invoked across the Web by anyone in the world. For example, a credit card company might provide a Web service to be called by retailers to validate card details. They are often used across companies' intranets, for use in internal applications and as a means of integrating disparate internal applications.

Web Services is built around three standards that define the format of the XML files needed to link clients to services:

For the latest specifications of WSDL, SOAP, HTTP and UDDI, see the Web site.