A Web service is a means of exposing application logic or data via standard protocols such as XML or SOAP (Simple Object Access Protocol). A Web service comprises one or more function endpoints, packaged together for use in a common framework throughout a network. Web services provide access to information through standard Internet protocols, such as HTTP/HTTPS. A Web Services Description Language (WSDL) contract is used to detail the input and output requirements for calling the interface. Consumers of the Web service can learn about the structure of the data the Web service provides, as well as all the details about how to actually consume this data, from the WSDL. A WSDL provides a detailed description of the remote interface offered from the Web service.
This simple concept provides for a very wide variety of potential uses by developers of Internet and intranet applications alike. Today, the Web services model is often the heart of the next generation of systems architecture because it is all of the following: