Create an Ajax mindreader application with E4X and Prototype, Part 1: Build the Twenty Questions infrastructure

XML seems like a natural format for passing Ajax data. However, to work with
XML in JavaScript using the Document Object Model (DOM) is not always the best way to handle this kind of
data. This has given rise to other choices, such as JSON, which provide a more
object-like feel for developers. Now ECMAScript for XML (E4X) combines many of the
best features of the DOM with extremely easy data binding to provide a more
straightforward way to deal with XML in the browser. In this two-part article
series, you'll learn to use both E4X and the Prototype JavaScript library to create
a simple Ajax mindreader application that plays Twenty Questions and learns about new objects as it goes along. Part 1 shows you how to create a system that takes an existing knowledge base and analyzes it to determine what the user may be thinking.