My Java Experience

Three forms of AJAX: Solid, Liquid and Gas.

Looks like today AJAX concept have several different interpretations. According to the way applications use XMLHttpRequest, we can distinguish three main strategies of AJAX integration:

- Application-specific JavaScript that play a role of presentation controller on the client-side.
- Component oriented form
- Sub-page oriented form.

The first form refers to pure JavaScript developments. Solutions, implementing this form are the most flexible and powerful. They allow creating amazingly rich user interfaces. However, because of well-known limitations of JavaScript, they are quite hard to develop, debug and maintain. In addition, if multi browser support is required, you will probably have to develop a second AJAX-free version of your UI.

Component oriented form is both flexible and easy to maintain. Components do not necessarily expose JavaScript to developers, thus making their job easier. Auto-complete or auto-validating text fields, AJAX-aware trees and updatable data grids are typical examples of this approach. Its main disadvantage is the scope that rarely exceeds a single component (or set of similar components).

The third form is sub-page oriented form of AJAX integration. It refreshes "zones" on the page. While being less powerful then other forms, it is ideally suited for upgrading existing projects. It does not have visible scope limitations and preserves the original MVC architecture (presentation controller stays on the server side). Another advantage of this form is graceful degradation possibilities. The same presentation code can support both AJAX and traditional modes.

Unfortunately, all those forms seem to be mixed up under the same buzzword and compete with each other in developers’ minds.
[source : theserverside.com ]