Before we look at the interface, we need to understand what REST is. In its simplest terms, REST is a set of six constraints, which when applied to an architecture (such as a web service) gives the basis of the RESTful style.

While it is outside the scope of this book to look at the architecture, there are many very good websites that cover what REST is. As far as we're concerned, we are interested in communicating with the web service.

REST services are typically transmitted using HTTP's GET and POST methods and return data in plain XML.