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AJAX technologies and applications

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Technologies

Ajax method is to use jointly various open and available standard technologies on most browsers on the market.

  • JavaScript is a programming language built into browsers. Programs written in this language are executed by the browser. It is used in particular to exploit the XMLHttpRequest and DOM. This is the Ajax keystone.
  • HTML and CSS for presentation. CSS (short for Cascading Style Sheets) is a data format used to create style sheets attached to web pages. It is used in Web applications to separate the content – changing – of web pages by their presentation, which is constant. It allows for savings on communications between the server and the web browser and set up a graphical map.
  • The DOM (acronym for “Document Object Model“) for dynamic display and interaction with data. This is a collection of objects where each object represents a structural or visual element of a web page or an XML document. It is used from an object oriented programming language such as JavaScript to inspect and modify the content of Web pages.
  • XMLHttpRequest is a programming object, used in JavaScript programs to ensure communication between the browser and a Web server. It is used for asynchronous communication: send requests to the server and trigger operations upon receipt of this response.
  • XML (abbreviation for Extensible Markup Language) is a markup language, and JSON (JavaScript Object Notation acronym) is a data format inspired by the syntax of JavaScript. They are used to structure the information sent by the web server. XML is accompanied by XSLT for its manipulation.

Ajax and traditional Web applications

Web Application versus an application using Ajax(The conventional model for a Web Application versus an application using Ajax, https://en.wikipedia.org/wiki/File:Ajax-vergleich-en.svg)

The classic Web applications allow users to make choices (follow a link, complete and submit a form) as a result of which a request is sent to the Web server. The server will respond to the request by sending a web page. A web page is sent in response to each manipulation, and the transmission of the web page from the server to the browser causes a much greater lag time when the page is rich in content and presentation (tables, colors, fonts character …).

In Web applications in Ajax, a Web page is sent only once. The page sent will contain a program written in JavaScript. When is being manipulated on the page by the user, the program in JavaScript sends requests to the Web server, the server will respond to requests by sending an XML document, the document does not contain presentation of information and the number of information it contains is often reduced, hence smaller latency than those of a traditional Web application.

Using JavaScript allows to induce requests during handling which otherwise are not provoked (because of the mechanisms used). This allows to implement features that are found only in Rich Internet Applications.

CSS style sheets are also used in the different pages of a Ajax Web application, in order to reduce latency in the initial sending of the page. Presentation of the information is extracted from different Web application pages, and placed in a single style sheet used for the different pages of the application.

Alternatives

Alternatives for the display of dynamic content within a web page are:

  • Flash and Flex (Adobe Systems);
  • JavaFX and Java Applet (Sun Microsystems / Oracle);
  • Silverlight (Microsoft);
  • XForms, a form standard proposed by the W3C.

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