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. Web services tend to fall into one of two
camps: big web services and RESTful web services. 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." 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 s