HTML and CSS Reference
In-Depth Information
XML (and the related XSLT technology)
Asynchronous data retrieval using XMLHttpRequest
Some of these technologies may be unfamiliar to you. That's okay at this point in your
Web development career. You're currently creating a strong foundation in XHTML and
CSS and may decide to continue your studies in the future and learn additional Web
technologies. Right now, it's enough to know that these technologies exist and what
they can be used for.
Ajax is part of the Web 2.0 movement—the transition of the Web from isolated static
Web sites to a platform that uses technology to provide rich interfaces and social net-
working opportunities for people. See
2005/09/30/what-is-Web-20.html for an intriguing article about Web 2.0 by Tim
O'Reilly, who was instrumental in the creation of the term “Web 2.0”.
Ajax is a Web development technique for creating interactive Web applications. Recall
the client/server model discussed in Chapters 1 and 9. The browser makes a request to
the server (often triggered by clicking a link or a submit button) and the server returns
an entire new Web page for the browser to display. Ajax pushes more of the processing
on the client (browser) using JavaScript and XML and often uses “behind the scenes”
asynchronous requests to the server to refresh a portion of the browser display instead
of the entire Web page. The key is that when using Ajax technology, JavaScript code
(which runs on the client computer within the confines of the browser) can communi-
cate directly with the server—exchanging data and modifying parts of the Web page dis-
play without reloading of the entire Web page. For example, as soon as a Web site
visitor types a Zip code into a form the value could be looked up on a Zip code data-
base and the city/state automatically populated using Ajax—and all this takes place
while the visitor is entering the form information before they click the submit button.
The result is that the visitor perceives the Web page as being more responsive and has a
more interactive experience. See for an example of
Ajax in action. As shown in Figure 11.19, hints are provided as you type the name of
a CSS property—without refreshing the page.
Figure 11.19
Ajax technologies
are used to update
the page as the
visitor types
Common Uses of Ajax
Developers are using Ajax to support the Web applications that are part of Web 2.0—
Flicker's photo sharing (,'s shared collection of
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