A Web service is a method of communication between two
electronic devices over the World Wide Web. A Web service is a software
function provided at a network address over the web or the cloud, it is a
service that is "always on" as in the concept of utility computing.
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, known by the acronym 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."
The W3C also states, "We can identify two major classes
of Web services, REST-compliant Web services, in which the primary purpose of
the service is to manipulate XML representations of Web resources using a
uniform set of "stateless" operations; and arbitrary Web services, in
which the service may expose an arbitrary set of operations."
