For several years, we've been hearing of the promise of enriched browsers that deliver fast, interactive, desktop-like GUI experiences. A small group of vendors has sprung up to provide the client and server software necessary for enriched browsing, and has coined an acronym - RIA, or rich Internet applications - for this approach. Macromedia, the pre-eminent RIA vendor, has succeeded in getting its Flash client on most desktops, integrated with Microsoft's Internet Explorer, the pre-eminent basic browser. And Microsoft has committed to integrating RIA functionality into its next-generation Longhorn client operating system.

Why, if Macromedia Flash is so widespread, are so few Web applications written to take advantage of its RIA features such as the ability to cache data and application logic on the client side for offline browsing? This is not to deny that Flash is leveraged in some Web applications, but most developers target only the common-denominator browser functionality found in Internet Explorer, Mozilla Firefox, Apple Safari and other baseline browsers.

Fundamentally, RIA hasn't dominated the Web because it can't be taken for granted. RIA assumes a client-side component, such as Macromedia Flash, or client-side support for a specification, such as Microsoft's Extensible Application Markup Language , which aren't integrated universally into all browsers. RIA, as practiced today, violates the "write once run anywhere" dictum of mass-market Web applications. Any approach that is predicated on downloadable components or future standards just isn't ready for Web prime time.

Recently a new acronym, Ajax (Asynchronous JavaScript + XML), coined by Web application design consultancy, Adaptive Path, has been jostling RIA for mindspace in the enriched browsing universe. Ajax represents a different and potentially more ubiquitous approach that's well within the capabilities of most of today's baseline browsers.

Ajax and RIA refer to the same core phenomenon - the enriched browser-oriented Web presentation tier. But Ajax references open industry standards, whereas RIA carries the unpleasant connotation of partially proprietary approaches from vendors such as Macromedia, Nexaweb Technologies, Altio and Laszlo Systems. Ajax encompasses standards-based client-side presentation using XHTML, HTML, Cascading Style Sheets and Extensible Stylesheet Language Transformations; standards-based client-side processing using JavaScript; and asynchronous data retrieval using XMLHttpRequest (supported in Internet Explorer and other baseline browsers).