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Thursday, September 23, 2010

The characteristics of Ajax applications

Ajax development and Maintenance Challenges Ajax has certainly raised awareness of the high potential of web applications. At the mean time, Ajax has also brought the usage of JavaScript and DHTML to a much deeper and broader level in application development. There are significant benefits of Ajax, butthere are also significant challenges. The biggest challenge of using Ajax is its scripting-based approach. Ajax requires developers to write a lot of JavaScript code. JavaScript code is hard to develop, debug,test and maintain. Java Script/DHTML is not standardized and there are incompatibilities between different browsers, different browser versions, and different operating systems.There is a severe lack of tools for developing, debugging and testing Java Script/DHTMLcode. There is also a lack of a robust component marketplace. By its definition, ascripting language emphasizes “quick and dirty” at the cost of code maintainability. Incontrast, a realprogramming language like Java and C++ emphasizes formality and strictness. For example, unlike Java or C++, Java Script is not strongly typed.Programming errors can only be uncovered at runtime. Java Script object properties and methods can be easily (and arbitrarily) modified regardless of a predefined interface –none of which is allowed in Java or C++.Secondly, Ajax itself does not provide rich user interface or incremental update capability. Developer must code such functionality using JavaScript and DHTML. There are various JavaScript libraries available that alleviate this issue to some degree, but theystill require developers to write JavaScript and thus do not solve the fundamental challenge.Thirdly, Ajax development model tends to break the “markup + logic” design pattern.”Markup + logic” is a well established design pattern that separates user interface from application logic. User interfaces are described as markup documents and application logic are written separately in a procedure language to control the behavior. In order to create rich user interface, a lot of Ajax developers embed significant amount ofJavaScript inside their web pages. Mixing Java Script with presentation breaks the clear separation and makes application even more difficult to develop and maintain.In a typical application life cycle, the most expensive part is not the initial development but the ongoing maintenance. How to overcome the above challenges and thusenable “manageable and maintainable Ajax” should be a topic of high priority and importance for any significant Ajax development project. Ajax Application Architecture Given the challenges associated with Ajax, it is particularly important to architect an Ajax applicationproperly. Otherwise the result can be either lackluster performance or code maintenance nightmare, or even both. There are two items impact Ajax application architecture significantly: the choice of an Ajax engine and client-side application logic implementation. Ajax Engine From the point of view of software architecture, the significant difference between an Ajax application and a classic HTML web application is the introduction of a client-side engine. This engine, which runs inside the Web browser, acts as an intermediary between the application’s UI and the server. User activity leads to calls to the client-side engine instead of a page request to the server. Likewise, data transfer takes place between the server to the client-side engine, rather than directly to the Web browser.

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