Abstract on web Technologies



web Technologies 



Abstract:

Today’s rich Web applications use a mix of Java Script and asynchronous communication with the application server.This mechanism is also known as Ajax: Asynchronous JavaScript and XML. The intent of Ajax is to exchange small pieces of data between the browser and the application server, and in doing so, use partial page refresh instead of reloading the entire Web page.

AJAX (Asynchronous JavaScript and XML) is a powerful Web development model for browser-based Web applications. Technologies that form the AJAX model, such as XML, JavaScript, HTTP, and XHTML, are individually widely used and well known. However, AJAX combines these technologies to let Web pages retrieve small amounts of data from the server without having to reload the entire page. This capability makes Web pages more interactive and lets them behave like local applications.

Web 2.0 enabled by the Ajax architecture has given rise to a new level of user interactivity through web browsers. Many new and extremely popular Web applications have been introduced such as Google Maps, Google Docs, Flickr, and so on. Ajax Toolkits such as Dojo allow web developers to build Web 2.0 applications quickly and with little effort. Unfortunately, the accessibility support in most toolkits and Ajax applications overall is lacking. WAI-ARIA markup for live regions presents a solution to making these applications accessible. A popular application that uses Ajax technology is Google Maps. The goal of this project is to develop an extension of Google Maps which includes viewing 360-degree ground-based panorama images. The project includes development of a client-side Ajax engine and user interface in JavaScript, and development of a back-end java servlet that serves panorama data and images.

Ajax:

A
s the Internet has become more mature, rich applications featuring responsive user interfaces and interactive capabilities have become increasingly popular. The capabilities represent a way to make programs easier to use and more functional, thus enhancing the user experience.

 Developers have used a variety of applications from companies such as Macromedia, Microsoft, and Sun Microsystems to add these capabilities in the past, as discussed in the “Developing Large-Scale Rich Web Applications” sidebar. However, Web applications have generally exhibited problems such as slow performance and limited interactivity, particularly when compared to typical desktop applications,noted Nate Root,research director for Forrester Research, a market analysis firm.Now, developers are going back to the future by building Web applications using Ajax (Asynchronous JavaScript and XML) ,a set of technologies mostly developed in the 1990s. A key advantage of Ajax applications is that they look and act more like desktop applications, according to Root. Proponents argue that Ajax applications perform better than traditional Web programs. As an example, Ajax applications can add or retrieve new data for a page it is working with and the page will update immediately without reloading. For instance, when users hold down the left mouse button and slide the cursor over an image on the
Ajax-based Google Maps beta site http: // maps. google.com) to retrieve a part of the map not shown on the screen, the updates occur smoothly and the image appears to move and change immediately. With typical Web applications, users must spend time waiting for entire pages to reload, even for small changes.
           
 When companies began working with the technology several years ago, before the approach even had the name Ajax, they used it for smaller, less important applications.  However, as the component technologies have improved, Google and a number of other companies have started using Ajax for more important enterprise applications. In addition to its map site, Google has worked with Ajax to build applications such as Gmail and Google Groups, a community and discussion service, said Bret Taylor, Google Maps product manager. Flicker uses Ajax in some parts of its Web site, on which user’s post and share photographs. For example, Ajax enables the site to let users add and view photo annotations. Expedia has produced features such as pop-up calendars on its travel site via Ajax.

All major browsers now support the technology. Thus, Ajax could pose a threat to Microsoft, Macromedia, and Sun. However, while some companies may decide Ajax is particularly useful for certain kinds of applications, industry observers say it won’t be suitable for all types. And in some cases, companies may use Ajax to complement other Web-application approaches. Meanwhile, Ajax still faces several technical challenges, such as usage complexity and security.

WHAT AJAX IS:
Developers use Ajax technologies to build Web applications with improved performance and interactivity, as well as responsive user interfaces. The applications offer functionality generally available in desktop software but not on the Web, which was designed for communications simplicity, not to enable the development of programs with enhanced capabilities.

Component technologies:

Most of Ajax’s component Web technologies were developed and standardized during the past 10 years. These technologies have improved recently, making them more suitable for enterprise use.

Dynamic HTML:
Ajax applications take advantage of dynamic HTML, which consists of HTML, cascading style sheets, and JavaScript glued together with the document object model. The tech- nology describes HTML extensions that designers can use to develop dynamic Web pages that are more animated than those using previous HTML versions. For example, when a cursor passes over a DHTML page, a color might change or text might get bigger. Also, a user could drag and drop images to different places.



XML:
Ajax uses XML to encode data for transfer between a server and a browser or client application. The W3C started work on XML in 1996 to enable cross-platform data interope -rability over the Internet. The consortium approved the standard’s first version in 1998. XML is a markup metalanguage that can define a set of languages for use with structured data in online documents.Any organization can develop an XML-based language with its own set of markup tags.

Cascading stylesheets:
A W3C standard since 1996, CSS gives Web site developers and users more control over how browsers display pages. Developers use CSS to create stylesheets that define how different page elements, such as headers and links, appear. Multiple stylesheets can apply to the same Web page.

Document object model:
          The DOM, a W3C standard since 1998, is a programming interface that lets developers create and modify HTML and XML documents as sets of program objects, which makes it easier to design Web pages that users can manipulate. The DOM defines the attributes associated with each object, as well as the ways in which users can interact with objects. DHTML works with the DOM to dynamically change the appearance of Web pages. Working with the DOM makes Ajax applications particularly responsive for users.

JavaScript:
Released in 1995 by Netscape and Sun, JavaScript interacts with HTML code and makes Web pages and Ajax applications more active. For example, the technology can cause a linked page to appear automatically in a popup window or let a mouse rollover change text or images. Developers can embed JavaScript, which is openly and freely available, in HTML pages. Ajax uses asynchronous JavaScript, which an HTML page can use to make calls asynchronously to the server from which it was loaded to fetch XML documents. This capability lets an application make a server call, retrieve new data, and simultaneously update the Web page without having to reload all the contents, all while the user continues interacting with the program. Enterprise application developers have become more interested in working with JavaScript because users have removed some of the technology’s bugs and developed workarounds for various problems.
Because JavaScript is a cross platform scripting language; Ajax applications require no plug-ins, unlike Macromedia Flash and other proprietary Web application technologies.

XMLHttp-Request:
Systems can use JavaScript-based XMLHttp Request objects to make HTTP requests and receive responses quickly and in the background, without the user experiencing any visual interruptions. Thus, Web pages can get new information from servers instantly without having to completely reload. For example, users of an application with XMLHttp Request objects could type in a centigrade amount in one box of a temperature-conversion application and have the Fahrenheit amount appear instantly in another box. Various browsers—including recent versions of Internet Explorer, Mozilla’s Firefox, Netscape, and Apple Computer’s Safari—work with XMLHttp- Request.  
         
Fig 1Figure1. In (a) a traditional Web application, user actions trigger an HTTP request to a Web server, which processes the request and returns an HTML page to the client. Additional requests lock up the application until the system updates the page. (b) Ajax applications create a JavaScript-based engine that runs on the browser.
 The engine intercepts user inputs, displays requested material, and handles many interactions on the client side. If the engine needs more data, it requests material from the server in the background, while the user continue to interact with the application


How does AJAX works?
A traditional Web application submits the HTTP request to the Web or the application server from the browser. An action, such as a mouse click on a hyperlink or a form submits, initiates the request. The server generates the HTTP response, and returns the requested page. Ajax Web applications add a bit of seasoning to this flow. Similar to a classic Web application, the application submits a request as a result of a user interaction. Instead of refreshing the entire page, Ajax refreshes only part of the page.

An Ajax-driven application submits the HTTP request asynchronously. So, instead of waiting for the entire page to load, the end user can continue interacting with the page. The Ajax engine is the key player in the Ajax model. The Ajax engine is a piece of code that is typically implemented in JavaScript, is downloaded along with the HTML page, and runs in the browser. The Ajax engine has multiple responsibilities (Figure 2):

  Fig 2.
1. Detecting user interactions. The engine detects and reacts to user interactions as they take place. For example, if the user hovers the mouse over a specific area, the Ajax engine recognizes the action and triggers an HTTP request.

2. Submitting HTTP request to the server. When the pre-defined user interaction takes place, the Ajax engine submits a request to the Web server asynchronously.

3. Handling HTTP response returned by the server. The engine handles markup returned by the Web or application server. For example, if the response is XML, the Ajax engine applies the XSL style sheet to it.
4. performing partial page refresh. The engine makes the necessary changes to the Document Object Model (DOM), which is the internal representation of the HTML docu- ment, thus updating the rendered page. For example, the engine can display a new layer of HTML containing the data returned from the server.



APPLICATIONS:
          BROWSERS THAT SUPPORT AJAX:
          Apple Safari 1.2 and above
         Konqueror
         Microsoft Internet Explorer (and derived browsers) 5.0 and above (Mac OS 9 or X version not supported)
         Mozilla/Mozilla Firefox (and derived browsers) 1.0 and above
         Netscape 7.1 and above
         Opera 7.6 and above
         Opera Mobile Browser 8.0 and above.
         Web Renderer (Java browser component)

WHO IS USING?

         Google Maps
         Google Suggest
         Gmail
         Flickr (Yahoo company)
         Amazon’s A9.com (search engine)
         Netvibes     Etc…,

THE UPSIDE:
Proponents say that Ajax applications perform better than today’s Web applications. Generally this is true because Ajax applications are more responsive to user actions and the programs don’t experience page-reloading-related interruptions, explained Jesse James Garrett, cofounder and director of user experience strategy for the Adaptive Path consultancy. Garrett coined the term Ajax earlier this year. Also, Garrett said, Ajax applications are usually fast because the approach minimizes traffic to the server by sending and requesting just the minimum amount of data needed. Proponents say another benefit of working with Ajax is that more developers have experience with its component technologies than with other Web-application- development approaches. In addition, said HÃ¥kon Wium Lie, chief technology officer for browser maker Opera Software, because Ajax works across platforms, developers generally can write applications once to run via the Web on many users’ systems, regardless of platform.

THE DOWNSIDE:
According to analyst Ray Valdes with market research firm Gartner Inc., developers can add Ajax techniques piecemeal to an existing system, one code snippet at a time. However, he added, trying to implement all the techniques at once in a complex project “approaches the rocket-science level of difficulty.” “Your average developer is not going to be able to figure it out,” Valdes said. “Only a small, elite group has the smarts to do it in a comprehensive, complete way.” In general, though, Garrett said, Ajax’s learning curve for professional designers is not steep. However, he noted, the technology is immature and still needs toolkits and frameworks. In addition, he said, “Because there are so few prebuilt Ajax interface components, developers will have to custom build most interfaces for each application. Some will be successful, some won’t.” Ajax also has raised some security concerns. For example, Forrester’s Root said, its component technologies have been around for years, but they are now being used in unproven ways that might make them more vulnerable to security breaches. “The two major compatibility issues with Ajax,” said Garrett, “are differences in JavaScript implementations across browsers and
providing alternate means of accessing the applications with older browsers that don’t fully support modern Ajax features. In both cases, additional development effort is required.” Another challenge, noted Sandy Leung, Yahoo’s product mana- ger for next-generation interfaces, is that users must get accustomed to Ajax applications that don’t perform like traditional Web applications. And because Ajax doesn’t reload entire pages to add new material, he said, search engines might not index some important information. Moreover, Ajax isn’t useful for some applications. For example, it can’t be used for audio and video streaming, as neither HTML nor JavaScript have an audio or video API, explained Sun senior staff engineer Tor Norbye.
WHAT’S NEXT?

Some sources say the recent attention to Ajax has also brought attention to rich Web applications, which will help vendors using other development approaches, Garrett said. According to Norbye, better browsers, tools, and network performance will improve Ajax’s capabilities in the future. Ajax could find various uses. For example, vendors could use it to build Web based versions of desktop applications. This way, companies could make software widely available to employees via a network and thus avoid spending the time and money required to install applications on every computer. Ajax also could be useful for the growing number of Web applications for mobile devices. However, predicted Root, while Ajax may prove interesting to developers now, they may turn to versions of Flash and other technologies in the future because, for example, Flash supports audio, video, advanced vector graphics, and other capabilities that Ajax can’t offer. Because they find it useful, companies will create more Ajax-based applications in the near future, predicted Kevin Lynch, Macromedia’s chief software architect.“We’re now entering a period of experimentation,” said Adaptive Path’s Garrett. “A lot of people in the past six months became aware of the possibilities that Ajax opens up for them. Developers are pushing at the boundaries of what they can do with it.” Ajax will do well as long as it is competitive with other approaches. For example, Google’s Taylor said, his company will use Ajax as long as it likes what the technology offers. He explained, “We will use whatever technology platform provides the richest user experience possible.”




CONCLUSION:

AJAX is most viable RIA technology so far. It’s getting tremendous industry momentum and several toolkit and frameworks are emerging. But same time AJAX has browser incompatibility and it is supported by Java Script which is hard to maintain and debug. It is a powerful technology for making dynamic web applications. AJAX applications can present Accessibility barriers. Simple changes to application design can make AJAX usable for all.DHTML Accessibility Techniques fit well with AJAX.

REFERENCES:

  • Jesse James Garrett, Ajax: A New Approach to Web Applications, Adaptive Path, Feb 2005,
http://www.adaptivepath.com
/publications/essays/archives
/000385.php.
  • Ajax, Wikipedia definition,
http://en.wikipedia.org/wiki
/Ajax_%28programming%29.
  • Stamey, J. and Richardson, T. 2006. Middleware development with AJAX. J. Comput. Small Coll. 22, 2 (Dec. 2006), 281287.
  • Doernhoefer, M. 2006. JavaScript. SIGSOFT Softw. Eng. Notes 31, 4 (Jul. 2006), 1624.
  • Adler, S. 2005. WebOS: say goodbye to desktop applications. Networker 9, 4 (Dec. 2005), 1826.
  • Yu, J., Benatallah, B., Casati, F., and SaintPaul, R. 2006. Open UP: an alternative approach to developing highly interactive web applications. In Proceedings of the 6th international Conference on Web Engineering (Palo Alto, California, USA, July 11 14, 2006). ICWE '06. ACM Press, New York, NY, 289296.
  • Google. “Google Maps”. 10 October 2006.
  • World Wide Web Consortium (W3C). Roadmap for accessible Rich Internet Applications (WAI-ARIA Roadmap) 20 December 2006. 17 January 2007
  • World Wide Web Consortium (W3C). 
  • Roles for Accessible Rich Internet Applications (WAI-ARIA Roles) 26 December 2006. 17 January 2007.
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