A Web service consumer can be a human user accessing the service through a desktop or wireless browser, it could be an application program, or it could be another Web service. A Web service is accessible over the Web. A Web service exposes an XML interface. A Web service is registered and can be located through a Web service registry. Web services communicate using XML messages over standard Web protocols.
Web services support loosely-coupled connections between systems.
Perhaps what is most intriguing about Web services is that it doesn't matter what technologies are used to build Web services. They have been using the Internet to automate supply chains and improve business process efficiency. Now businesses are intrigued by the Web services approach to Internet computing. The Web services computing model promises even better cross-business integration, improved efficiency, and closer customer relationships. But in order to make the Web services model palatable, businesses must be able to leverage existing application assets and expose them as Web services.