A RESTful web service (also called a RESTful web API)
is a web service that is implemented using HTTP and the principles
of REST. It is a collection of resources with four defined aspects:
Base URL for the web service, such as:
http://example.com/resources
Internet media type of the data supported by the web service.
This is usually XML, but can be any other valid Internet media type
providing that it is a valid hypertext standard.
Set of operations supported by the web service using HTTP methods
(for example, GET, PUT, POST, or DELETE).