The popularity of applications such as Google Maps and Flickr has Web developers flocking to the technologies that make these rich, interactive programs work. But industry watchers caution the Web scripting components known collectively as Asynchronous JavaScript + XML can be more complex - and less network friendly - than they might first appear.

AJAX refers to a set of technologies including JavaScript, XML, Dynamic HTML and asynchronous XML/HTTP calls. Jesse James Garrett of consulting firm Adaptive Path coined the term AJAX in a February 2005 essay to describe the assortment of browser-native tools and technologies that make applications such as Google Maps and Google Suggest as slick and responsive as they are.

Google Maps sends an XML datastream to the browser to let users pan around the globe and zoom in on maps and satellite images with an ease that is expected of a desktop application, not a Web application that has to continually fetch content from a remote server. Google's Suggest application uses JavaScript to offer search suggestions and quantify search result sets as a user begins to type a query in the search box.

Google wasn't the first to exploit these technologies, but the company did so in a massive scale and in a very public way. Amazon's A9.com search engine also makes use of AJAX-style development, as does photo-sharing site Flickr.

The corporate role

Increasingly, corporations are considering the role AJAX technologies can play in businesses that aren't catering to millions of consumers. Industry experts say there's a place for AJAX in the enterprise, but IT staffs need to evaluate and implement the technologies in a prudent way.

The first step is assembling a cross-functional team, says Joe Skorupa, research vice president at Gartner. It's important for companies to get Web developers together with IT staff who know about security, database design, server administration, networks and desktop administration, he says.

Developers need to design AJAX applications from the start to account for the number of TCP connections that could potentially be open at any one time, as well as the effect of continuous content refreshes on server loads. Adequate prototyping and testing are imperative, he says. "If you do that, you can come up with some cool stuff that will delight your users."

AJAX is less about any single technology than it is an approach to developing applications that are more responsive than typical HTML pages. One of the most-appealing features is that AJAX applications don't require plug-ins or other code to be installed on client machines.

Instead of using the familiar page-submit/page-refresh model, AJAX applications keep content current by refreshing only the parts of the screen that have changed. In addition, AJAX applications use the power of the user's PC and Web browser to perform many of the tasks that traditionally are done on a server. For example, a user can sort data or edit tables without sending or receiving data from a server.

Companies are looking to incorporate AJAX technologies into new and existing software programs. For instance, a company could revamp a Web application by adding real-time updates of such data as account balances or inventory levels. Instead of a user having to request this information, a developer could design the application to automatically poll a server for changes every 15 seconds, or go looking for an update every time a user moves a cursor over the data field.

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