1.Introduction Of AJAX

Ajax Overview:

Ajax (asynchronous JavaScript and XML), or AJAX, is a group of interrelated web development techniques used for creating interactive web applications or rich Internet applications. With Ajax, web applications can retrieve data from the server asynchronously in the background without interfering with the display and behavior of the existing page. Data is retrieved using the XMLHttpRequest object or through the use of Remote Scripting in browsers that do not support it. Despite the name, the use of JavaScript, XML, or its asynchronous use is not required.AJAX is not a new programming language, but a technique for creating better, faster, and more interactive web applications. 

                (Asynchronous JavaScript and XML) is a competitor to Applets. AJAX is not a language or a software package or even an interface. It’s a word someone invented for the generic concept of having JavaScript talk directly to the server without reloading the HTML page. There are any number of possible ways of implementing AJAX. The most common is to use the non-standard XmlHttpRequest class, which is available from JavaScript in most major browsers. 

                The major defining characteristic, though, is the asynchronous aspect of the technology. Even XML is in there by coincidence; people describe things as “AJAX” applications when they don’t use XML at all. There is no new language or file format here. There’s no specification; no definition of what AJAX is or is not. There are no special tools. There’s no visual appearance that could be created except what you could do with a web browser, HTML, JavaScript, and CSS anyway. In fact, if you were allowed to stub out the data, you could write any AJAX application with only those basic client-side web technologies. 

AJAX is typically a generic JavaScript program to allow thin clients to do field validation (by asking the server) without refreshing the entire page. Google uses it for maps. It works by sending standard HTTP queries to the server. Your application specific code all lives on the server. 

Note:

AJAX is a browser technology independent of web server software.

AJAX is Based on Web Standards 

AJAX is based on the following web standards: 
• JavaScript 
• XML 
• HTML 
• CSS 
The web standards used in AJAX are well defined, and supported by all major browsers. AJAX applications are browser and platform independent. 

AJAX is About Better Internet Applications 

Web applications have many benefits over desktop applications; they can reach a larger audience, they are easier to install and support, and easier to develop. However, Internet applications are not always as "rich" and user-friendly as traditional desktop applications. With AJAX, Internet applications can be made richer and more user-friendly.