XML is one of the most important tools in Ajax development. This mark-up language is more than just a simple carrier of information as it can practically take the center stage in an application. When you are running in a database intensive application, XML becomes the most important part of the Ajax based application. One of the biggest reasons why most developers have opted to use XML for Ajax is its ability to be used freely in any languages. That means XML could easily be integrated in any languages and development techniques.