A web service is a software system designed to support interoperable computer to computer interaction over the internet or private network. A web service has an interface that is described in a machine readable format such as WSDL (Web Service Description Language). Other systems interact with the Web service in a manner defined by its interface using messages that are encapsulated and transfered using standard transport protocols (such as SOAP). These messages are typically composed with XML and are transferred using HTTP. Software applications written in a variety of languages and running on varying platforms use web services to exchange data over a network. This interoperability between platforms and systems is a key feature of web services.