A web service (also webservice) is defined by the W3C 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.

Web services are frequently just Internet Application Programming Interfaces (API) that can be accessed over a network, such as the Internet, and executed on a remote system hosting the requested services. Other approaches with nearly the same functionality as web services are Object Management Group's (OMG) Common Object Request Broker Architecture (CORBA), Microsoft's Distributed Component Object Model (DCOM) or Sun Microsystems's Java/Remote Method Invocation (RMI).

Web services can be written in two ways:

• Developer using bottom up method first writes the implementing class in a programming language and then uses WDSL generating tool to expose its methods as web service[1]. This is often simpler way.
• Developer using top down method first writes the WSDL document and then uses code generating tool to produce the class skeleton that she later completes. This way is more difficult but produces cleaner designs.