Asynchronous JavaScript and XML (Ajax)
Ajax is an acronym that stands for Asynchronous JavaScript and XML. To understand how Ajax works, you reflect on the three parts of its acronym, which are (1) asynchronous, (2) JavaScript, and (3) XML.
Asynchronous
Asynchronous means that different elements onscreen can communicate with data sources and update their appearance independent from other objects onscreen. No longer is it necessary to refresh the entire screen when there is new data to display.
JavaScript
JavaScript is the client-side programming language used by Ajax. Client-side means that the script runs locally in the browser on the user's PC. On this page that you are reading now, for example, there is an Ajax component called a Collapsible Panel Group that is used to create the sliding navigational elements in the left sidebar. Notice how you can click the plus signs to expand the menu, or click the minus signs to collapse it. The program that does the expanding and contracting is written in JavaScript. The script grabs hold of the menu elements by their IDs and makes them visible (or not) by manipulating the document's style sheet paremeters depending on whether you click the plus sign to make part of the menu visible, or click the minus sign to collapse it.
XML
XML stands for extensible markup language. Ajax elements can read information from XML data sources and display it onscreen in powerful ways. In the example below, a collapsible panel group is fed by an XML file consisting of the dissertations written by students in our educational technology program. Notice how you can click on the dissertation titles to expand or collapse each entry. After you play with these sliding panels, take a look at the XML source file, which is at www.udel.edu/education/dissertations.xml.
Doctoral EPP Thesis by {author}
{description}