As you work with AJAX, you may hear of related technologies that you can use with AJAX. They fit into two main groups: mature technologies that are widely available in many browsers today, and new technologies that are available only on a specific browser. The mature technologies include Java and Flash. (Flash is the most important because its plug-in is widely installed, and its design is optimized for providing interactive elements and animations to Web sites.) Java can also be used to add interactivity to sites, but its popularity has waned over the past five years, and it's no longer installed by default everywhere.

Combining AJAX with Flash

Flash makes a good partner with other AJAX techniques because it provides a number of features that are not available with pure JavaScript. These include a canvas on which images can be added and positioned and a drawing API that can be used for creating graphics. In addition, Flash has the ability to stream video and sound, and it includes support for vector animations. The biggest drawback of Flash is that it adds a new, separate development environment, and although you can make calls between the JavaScript on your page and the ActionScript of your Flash movie, it's not tightly integrated with the rest of your page. Flash also has a different look than the rest of the elements on an HTML page, which makes it hard to deliver a consistent feel and operation when using it for small elements within a bigger picture.

The drawbacks of Flashpoor JavaScript integration and a different look and feelare not insurmountable, but they do lead many people to pick a complete Flash solution when they need to do anything complicated. This helps control complexity, but it leaves you fully tied to a single vendor and means that you have to use Flash remoting for your communications layer instead of AJAX. Adding Flash to your AJAX application gives you the ability to support many graphical tasks that would be impossible without it, but be prepared for a more complex design and debugging process.

Scalable Vector Graphics (SVG)

The new technologies in the browser world are not as widely deployed as Flash, and some, like Microsoft's Extensible Application Markup Language (XAML), have had only beta releases. They do have the benefit of being fully integrated into the browser, making them fully scriptable with JavaScript and available as first-class elements on Web pages. Scalable Vector Graphics (SVG) is a new W3C standardized language for creating vector graphics. It has many of the same features as Flash, allowing for animations and interactive graphical elements to be added to the page. SVG avoids many of Flash's problems because it uses JavaScript for scripting; in addition, it can be embedded directly into an HTML page and modified just like any other element.

SVG's biggest problem is that browser support has been slow to develop; a plug-in from Adobe currently supports many of its features, but it leaves some of the same integration problems as Flash. The next versions of both Firefox and Opera browsers will have built-in support for SVG, but that still leaves it as a niche technology that can be used only on internal projects.

SVG is also missing a canvas element, so there is no way for users to draw on elements, as can be done with Flash. To address this, a bitmap canvas was created by Apple for its Safari browser. This effort has since been codified by the Web Hypertext Application Technology Working Group (WHATWG). This group is supported by many browser developers, including Mozilla and Opera, so support will be forthcoming in new releases of these browsers; however, support by Internet Explorer seems less certain.

XML User Interface Languages

Many of the new technologies are missing widespread browser support, and XML-based user interface languages are no exception. These languages, which include Mozilla's XML User Interface Language (XUL) and XAML, add the ability to describe normal application elements (such as menus, scrollbars, text boxes, and buttons) in an easy-to-use XML markup. Microsoft and Mozilla built their XML languages to allow for the creation of highly interactive rich applications that look and feel much like native applications right out of the box. However, because they are supported only by a single vendor, they do create problems of lock-in and tie you to a specific browser. This lock-in makes for a much less compelling solution than widely compatible solutions built on top of JavaScript and HTML.

XUL was created to define the user interface of Mozilla's browser and has been available for a number of years. Recently, it has begun to gain momentum as Firefox has increased in popularity, but it will never be able to move beyond niche products until other browsers support the language. XAML was created by Microsoft as part of its .NET effort, and it is scheduled to be released as part of Windows Vista. It's hard to know what its effect will be until it's widely released and until we know how accessible it will be to Web developers.

The rise of popular new Web browsers has led to the creation of exciting new Web technologies. The biggest problem is that most haven't made it beyond being implemented in a single browser. As support for these new technologies increases, they may become larger players, adding in the technology needed to increase interactivity beyond the level that AJAX and dynamic HTML (DHTML) can reach on their own.