Web services are distributed application components that are externally available. You can use them to integrate computer applications that are written in different languages and run on different platforms. Web services are language and platform independent because vendors have agreed on common web service standards. A web service is typically an application programming interface (API) or Web API that is accessed via Hypertext Transfer Protocol (HTTP) and executed on a remote system, hosting the requested service.

The W3C defines a "web service" as "a software system designed to support interoperable machine-to-machine interaction over a network. It has an interface described in a machine-processable format (specifically Web Services Description Language WSDL). Other systems interact with the web service in a manner prescribed by its description using SOAP messages, typically conveyed using HTTP with an XML serialization in conjunction with other Web-related standards."

Unlike traditional client/server models, such as a Web server/Web page system, Web services do not provide the user with a GUI. Web services instead share business logic, data and processes through a programmatic interface across a network. The applications interface, not the users. Developers can then add the Web service to a GUI (such as a Web page or an executable program) to offer specific functionality to users.

Web services allow different applications from different sources to communicate with each other without time-consuming custom coding, and because all communication is in XML, Web services are not tied to any one operating system or programming language.

The Role of Web Services on Mobile Platform

Web services are an emerging technology that provides interoperability between applications running in different platforms. The Web services technology provide the best approach to Service Oriented Architecture envisio n of component collaboration for better business requirements fulfillment in large enterprise systems. The challenges in implementing Web services consuming clients for low-resources mobile devices connected through unreliable wireless connections are delimited. The paper also presents a communication architecture that moves the heavy load of XML-based messaging system from the mobile clients to an external middleware component. The middleware component will act like a gateway that lightly communicates with the device in a client- server manner over a fast binary protocol and at the same time takes the responsibility of solving the request to the Web service. Keywords: Web Services, SOA, Mobile Computing, Mobile Devices.