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AJAX – The Most Promising Web Development with Web 2.0
AJAX is the acronym coined from asynchronous JavaScript and XML. This expression represents one of the most important current devolopments of the World Wide Web and accordingly what circulates in the media as Web 2.0.
AJAX – a Short Introduction
Looking back on the history of the Internet, the introduction of the World Wide Web in 1990 marks one of the most important milestones. With the introduction of the World Wide Web it became possible to attractively display content and, above all, to connect information. In order that, also technically unexperienced users could access the worldwide information network. However, the World Wide Web used to be exclusively static. Because of several constraints with static sites, a programming environment on the client's side quickly evolved. JavaScript, VBScript, Java Applets, ActiveX Control and several other technologies have been developed since arround 1995.
All these technologies were aiming at transfering activity from the server to the client. Since the year 2000, however, several problems with the client's technology have resulted in transferring more activity back to the server again. Proprietary standards as well as the market policy and last but not least security problems with the client have reduced the acceptance of client technology. In the last years, however, the hysteria around client-sided technology has died away and modern Web applications use client-sided (today almost exclusively JavaScript) as well as server-sided technology. The corresponding tasks are reasonably shared.
If you want to develop a modern Web application today, you will (fortunately) find a relatively homogeneous environment. Only a short time ago, this was definitely not the case.
What Is AJAX?
Concerning the transfer, the Internet is now based on TCP/IP. These abbreviations stand for Transmission Control Protocol / Internet Protocol. This protocol describes a package-oriented data transfer. The data are devided into smaller units and independently from one another sent to the corresponding recipient. Only with the recipient are the data reassembled. The main problem with this kind of communication is that there is no permanent connection. Indeed, it is possible to establish a virtual connection between sender and recipient on the basis of application logs (e.g. with Internet telephony or remote control mechanisms like Telnet and SHH) but only on the basis of transport protocols such a connection does not exist.
However, the protocol of the World Wide Web – HTTP – is a connectionless protocol. With other words: with this protocoll no virtual connection between the server and the client is established.
With this kind of stateless communication a server basically cannot identify whether a browser has already requested a Web site prior to the actual request. From your experience with the WWW you, of course, know that also with Web sites it is possible to find out whether a client has already requested sites from a server beforehand. This is essential with sites where only legitimate users have access to restricted contents. The legitimation procedure, however, is not realised by TCP/IP and accordingly HTTP but by techniques based on these protocols - like Cookies for instance. Moreover, stateless communication also means the complete transfer of an entire Web page as soon as information are exchanged between server and client.
How Does AJAX Come into Play?
AJAX is an approach in order to solve this problem. Concerning the classical cycle of data communication between server and client, it is always necessary to transfer an entire Web page as an answer if an information is requested from the Internet. With AJAX, however, it is possible to only send the very part of a Web page which has to be exchanged. The other parts of the page which do not have to be refreshed remain unchanged. Thus, it is obvious that the volume of data to be sent and, above all, the reaction time of Web application can be significantly reduced.
Imagine a Web form, for example, where the user has to fill in a licence plate number and in response the corresponding district should be displayed. With conventional Web applications it is necessary to request an entire new Web page from the server and display it to the client. Therewith, older information must be preserved (e.g. entries in other form fields the client has already made). This means, data are unnecessarily transfered to the server and returned unchanged. With AJAX exclusively the new information is requested from the server and, consequently, integrated into the existing Web page.
Indeed, this has already been possible in case only few data have to be kept available in order to be sent to the client and to integrate them into the Web page with Javascript and accordingly DHTML. However, this approach is not practical with larger volumes of data.
With AJAX data are only requested unless they are are required. Using DHTML effects, these data are consequently integrated into the designated areas of the Web site. With AJAX not only the Web browser and the Web server interact with one another but also Web site objects can communicate with the server independendly from this interaction. These objects are accessed (XMLHttpRequest) with JavaScript, for instance, if a specific function/service in the Web site is requested. This XMLHttpRequest object is the crux of the whole AJAX technology. Additionally, next to AJAX XHTML and accordingly HTML, XML, JavaScript and Style Sheets are considered further core technologies. In the context of AJAX, the technology used with the server is not explicitly specified. It is irrelevant whether PHP, ASP.NET, Java-Servlets or JSP is used. The choice is yours.
New from Old?
Considering the core technologies of AJAX you will notice that AJAX presents only few new approaches. Therefore, critics refer to AJAX as a marketing gimmick for existing technologies. However, supporters argue that because new technologies are not necessary AJAX is easy to implement into an existing environment. Concerning the success of AJAX the supporters might be right.
What Problems Are to Face with AJAX?
Beyond doubt, AJAX is the revolution of the World Wide Web. With AJAX Web applications that intensively interact with the user are accelerated to a degree almost comparable to desktop applications. This is going to change the way people use the World Wide Web. In the future, users will become spoiled because of AJAX applications. This means AJAX applications will set the point of reference for the user performance and users will expect this Web performance with all Internet applications. However, a constantly fast and problem-free transmission of data with a network like the Internet can self-evidently not be implied.
Application developers will have to find new ways for the interaction with the user as well as the user guidance. However, AJAX brings up further problems. The key word is Web accessibility. Page readers do possibly not work with dynamically generated content. Furthermore, search engines will also face problems with dynamic content and last but not least browser bookmarks will not work with AJAX applications. Likewise, the function of the back button is not functional with AJAX applications.
Concerning these problems AJAX developments (especially AJAX frameworks) will bit by bit provide or already have provided solutions. However, the use of AJAX will still bring up a row of problems to face. The main problem is that AJAX will only work if the necessary technical preconditions are ensured on the client's side: If Javascript is activated, a modern browser is in use supporting the XMLHttpRequest object, DHML effects are correctly supported and the user has not deactivated these functions. Particularly with companies where the internal firewall does not allow the use of Javascript AJAX application will still face problems.
Conclusion
Problems are there in order to be solved. All in all, AJAX is one of the most promising Web developments of the past years. Now, it is possible to finally counter the slow performance of Web application during the interaction with the user.
02/2007, Ralph Steyer
| | Ralph Steyer is free-lancing as a software engineer and consultant.
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