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Different Technology Options for AJAX

Considering that AJAX represents a Web application model that is defined by partial screen update and asynchronous communication, there are different technologies for building the AJAX client engine, of which JavaScript, Java, and Flash are the most commonly used. Likewise, these three technologies are the most widely used in building AJAX applications.

The Java approach ("Asynchronous Java + XML")
The Java approach typically uses a browser-based lightweight Java engine for client side processing, such as UI rendering, performing partial screen refresh and asynchronous server communication. In this approach, the UI can be defined using XML, whereas client-side application logic is programmed using standard Java.

Examples available over the Internet include:

• Artstor.org (http://www.artstor.org): a digital library of hundreds of thousands of pieces of art work and related tools.
  
• Map of the Market (http://www.smartmoney.com/marketmap/): an interactive map showing an aerial view of 1,000 U.S. and international stocks

The JavaScript/DHTML approach ("Asynchronous JavaScript + XML")
The JavaScript/DHTML approach typically uses a browser-based lightweight JavaScript library for client side processing, such as performing partial screen refresh and asynchronous background network communication. In this approach, the UI is typically defined by using DHTML and client-side application logic is programmed using JavaScript.

Some examples include Google Map (http://map.google.com) and Google Suggest (http://www.google.com/webhp?complete=1&hl=en).

The Flash approach ("Asynchrounous ActionScript + SWF")
The Flash approach typically uses a browser-based Flash engine with an ActionScript library for client side processing. In this approach, the UI is typically defined using SWF (a Macromedia proprietary binary format for defining Flash based movies) on the client side, and the client-side application logic is programmed using ActionScript.

Some examples include BroadMoor Hotel (http://www.broadmoor.com/), a Flash-based interactive hotel reservation system.

Strength and Weakness of Different Options
Each of the three AJAX options has its own strengths and weaknesses, making each one suitable for different applications. The following table summarizes their strengthes and weaknesses:

Option	Strength	Weakness
Java	Robust performance and reliability Ease of maintenance due to object-oriented programming Good for Java developers	Requires Java programming skills
DHTML/JavaScript	Fits well with existing HTML Web sites/Web applications Good for DHTML Web developers	JavaScript/DHTML code is hard to maintain and not designed for team development Performance and functionality limitations
Flash	"Sexy" animations Good for graphics designers	ActionScript code is hard to maintain and not designed for team development Performance and functionality limitations

The Java approach is capable of delivering good performance and functionality due to binary execution, multi-threaded computing, and the industrial strength of Java Virtual Machine. Applications written in Java are easy to develop and maintain because of the object-oriented programming nature of Java. It is good for enterprise Java developers who have Java programming skills. On the other hand, the Java programming skills requirement is also its weakness, because developer skill set requirements are higher than scripting. Historically, JVM compatibility in various browsers has been a significant issue for this approach. However, there are solutions available for these problems. One solution is to utilize a lightweight, JDK 1.1-compatible Java engine that is guaranteed to run inside all browser-based JVMs. This Java engine would abstract developers away from the traditional problems, enabling the development and universal deployment of Web applications by leveraging the strength of Java.

The DHTML/JavaScript approach fits well with existing HTML Web applications. It is natural for an existing HTML developer to write JavaScript, and the least expensive way of adding interactivity to an existing HTML application. In general, this approach requires the download of (potentially large) JavaScript libraries to compensate for the differing capabilities of the client browsers. The resulting applications are as rich as the underlying browser will allow. This approach can be problematic in large scale business applications due to difficulties developing and maintaining JavaScript, as well as performance/functionality limitations of DHTML.

The Flash-based approach is good for applications that require a "sexy" look and feel. It is a natural option for graphics designers. Flash enables developers to create very rich user interfaces, given Flash's heritage as a "movie engine." To date, Macromedia has targeted Flash for three use cases in the context of applications: guided selling, guided forms, and dashboards—primarily consumer facing or data visualization applications. Flash applications can access Java and .NET objects running on the server asynchronously. The major limitations of this approach are ActionScript and the limited capability of the Flash engine. ActionScript is a proprietary scripting language developed by Macromedia. It is easier to do scripting than programming for simple tasks, but developing and maintaining many scripts is difficult and expensive for more complex applications. Flash is not an industrial-strength virtual machine like JVM or .NET CLR; as a result, there are functionality and performance limitations for Flash-based applications.

There is no doubt that all three approaches are viable and each has success stories to prove it. However, choosing the wrong approach for the job also can be devastating.

Taking AJAX a Step Further

AJAX addresses some of the problems of the Web today, but there are still significant problems that AJAX does not address. For example, how do you make Web applications offline available? How do you enable server-initiated communications? How do you guarantee consistent performance, as well as reliability for Web applications, given that HTTP is not reliable and Internet performance is inherently limited by network conditions?

AJAX itself is not the destiny, but rather a leading indicator of how the Web application model is evolving. All of the above problems must be addressed for the Web to become a truly available, reliable, and performance infrastructure for software applications.

Conclusion

AJAX represents a generic application model that would enable more interactive, more responsive, and smarter Web applications. AJAX is not tied to a particular programming language, data format, or network object and is defined by two core attributes: partial screen update and asynchronous communication. There are three approaches to build and deploy AJAX applications: DHTML/JavaScript (Asynchronous JavaScript + XML), Java (Asynchronous Java + XML), and Flash (Asynchronous ActionScript + SWF). Each approach has its strengthes and weaknesses; as such, customers should evaluate and choose carefully.

This article originally appeared on EarthWeb's Developer.com.