How does it works:-

Ajax uses a programming model with display and events. These events are user actions, they call functions associated to elements of the web page.Interactivity is achieved with forms and buttons. DOM allows to link elements of the page with actions and also to extract data from Xml files provided by the server.

To get data on the server, XMLHttpRequest provides two methods:- open: create a connection.- send: send a request to the server.Data furnished by the server will be found in the attributs of the XMLHttpRequest object:- responseXml for a Xml file or- responseText for a simple text.Take note that a new XMLHttpRequest object has to be created for each new file to load.

We have to wait for the data to be available to process it, and in this purpose, the state of availability of data is given by the readyState attribute of XMLHttpRequest.

States of readyState follow (only the last one is really useful): not initialized.

1: connection etablished.
2: request received.
3: answer in process.
4: finished.

What is Ajax in depth?

Ajax is a set of technologies, supported by a web browser, including these elements:
Html and CSS for presenting.

JavaScript (ECMAScript) for local processing, and DOM (Document Object Model) to access data inside the page or to access elements of Xml file read on the server (with the getElementByTagName method for example)...

The XMLHttpRequest class read or send data on the server asynchronously. optionally...
The DomParser class may be used PHP or another scripting language may be used on the server.

XML and XSLT to process the data if returned in Xml form.

SOAP may be used to dialog with the server. The "Asynchronous" word, means that the response of the server while be processed when available, without to wait and to freeze the display of the page.

Why to use Ajax ?

Mainly to build a fast, dynamic website, but also to save resources.For improving sharing of resources, it is better to use the power of all the client computers rather than just an unique server and network. Ajax allows to perform processing on client computer (in JavaScript) with data taken from the server. The processing of web page formerly was only server-side, using web services or Php scripts, before the whole page was sent within the network.But Ajax can selectively modify a part of a page displayed by the browser, and update it without the need to reload the whole document with all images, menus, etc...For example, fields of forms, choices of user, may be processed and the result displayed immediately into the same page.

Brief history of Ajax:-

Ajax is only a name given to a set of tools that were previously existing.The main part is XMLHttpRequest, a class usable in JavaScript , that was implemented into Internet Explorer since the 4.0 version.The same concept was named XMLHTTP some times, before the Ajax name becomes commonly used.The use of XMLHttpRequest in 2005 by Google, in Gmail and GoogleMaps has contributed to the success of this format. But this is the name Ajax itself that made the technology so popular.

JavaScript and Server Technology Independent Frameworks:-

Many AJAX frameworks and libraries rely solely upon JavaScript and contain no server components and therefore server technology dependencies. Such AJAX libraries and frameworks include TIBCO General Interface, dojo Toolkit, MochiKit, and JackBe. Such frameworks are agnostic as to what server side technology you choose to use. Usually such frameworks are optimized to consume XML, though JSON is becoming popularized as well. Even Microsoft Atlas is, in part, positioned as having JavaScript libraries that can run without dependence on its .NET servers (though Altas perhaps works best with .NET services behind it).

Ajax Framework:-

Ajax is a technology to build dynamic web pages on the client side. Data is read from the server or sent to the server by JavaScript requests. However, some processing at the server side is required to handle requests, i.e., finding and storing the data. This is accomplished more easily with the use of a framework dedicated to process Ajax requests. In the article that coined the "Ajax" term, J.J. Garrett describes the technology as "an intermediary...between the user and the server."

This Ajax engine is intended to suppress waiting for the user when the page attempts to access the server. The goal of the framework is to provide this Ajax engine and associated server and client-side functions.

What's AJAX?

AJAX (Asynchronous JavaScript and XML) is a newly coined term for two powerful browser features that have been around for years, but were overlooked by many web developers until recently when applications such as Gmail, Google Suggest, and Google Maps hit the streets.

The two features in question are that you can:

A). Make requests to the server without reloading the page

B). Parse and work with XML documents