The Xtended Services are a set of RESTful APIs that allows resources to be defined and addressed over HTTP with simple XML. This approach requires less client-side software to be written than other approaches and is the overwhelming choice for developers to create Web Applications.
There are four parts to the Xsi that are designed to work together to create rich web applications. The four parts are described in their own sections reachable from below. It is recommended that a new developer begin with Xsi-Actions to build a knowledge base. Developers only interested in IVR type applications can just look at Xsi-Media, but most likely will also need Xsi-Actions to create the applications they desire.