4.Ajax Architecture

        From a software architecture point of view, following are ways in which AJAX differs from today's Web application architecture by adding a client-side engine:
  1. Use of a client-side engine as an intermediate between the User Interface (UI) and the server;
  2. User activity leads to program calls to the client-side engine instead of a page request to the server;
  3. XML data transfer between server and the client-side engine.

The client engine is the key to the AJAX model. Without this engine, every user event must go back to the server for processing. User interaction is tightly coupled with server communications—the client engine unlocks this dependency. This engine, while running inside a Web browser, gives the browser the "extra" intelligence to perform a "partial screen update" instead of a "full page refresh." This engine also communicates with the server in the background, decoupling user interaction from server communications.

Figure 3: Classic Web Application Architecture
Figure 4: Ajax Architecture