Instead of loading a webpage at the start of the session the browser loads an Ajax engine written in Java Script and usua lly tucked away in a hidden frame This engine is responsible for both rendering the interf ace the user sees and communicating with the server on the users behalf. The ajax engine allows the user's interaction with the application to happen asynchronously inde pende nt of communication with the server. so the user is never staring at a blank browser window and an hourg lass icon, waiting around for the server to do something classic web application model (synchronous) client user activity user activty user activity me system proce system pr server Ajax web application model (asynchronous) client browser UI user activity 二 Ajax engine dient-side processing time server process processing processing Figure 2: The synchronous interaction pattern of a traditional web application (top)compared with the asynchronous pattern of an Ajax application( bottom)Instead of loading a webpage, at the start of the session, the browser loads an Ajax engine — written in JavaScript and usually tucked away in a hidden f rame. This engine is responsible for both rendering the interface the user sees and communicating with the server on the user’s behalf . The Ajax engine allows the user’s interaction with the application to happen asynchronously — independent of communication with the server. So the user is never staring at a blank browser window and an hourglass icon, waiting around for the server to do something. Figure 2: The synchronous interaction pattern of a traditional web application (top) compared with the asynchronous pattern of an Ajax application (bottom)