Information AboutWeb Application |
| CATEGORIES ABOUT WEB APPLICATION | |
| world wide web | |
| software architecture | |
| web applications | |
| web development | |
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HISTORY In earlier types of Client-server computing, each application had its own client program which served as its User Interface and had to be separately installed on each user's Personal Computer . An upgrade to the server part of the application would typically require an upgrade to the clients installed on each user workstation, adding to the support cost and decreasing productivity. In Contrast , web applications dynamically generate a series of Web Page s in a standard format supported by common browsers such as HTML / XHTML . Client-side Scripting in a standard language such as JavaScript is commonly included to add dynamic elements to the user interface. Generally, each individual web page is delivered to the client as a static document, but the sequence of pages can provide an interactive experience, as user input is returned through web Form elements embedded in the page markup. During the session, the web browser interprets and displays the pages, and acts as the ''universal'' client for any web application. INTERFACE The web interface places very few limits on client functionality. Through Java, application-specific methods such as drawing on the screen, playing audio access to the keyboard and mouse are all possible. General purpose techniques such as . Ajax , a web development technique using a combination of technologies, is one example. TECHNICAL CONSIDERATIONS A significant advantage of building web applications to support standard browser features is that they should perform as specified regardless of the operating system or OS version installed on a given client. Rather than creating clients for Windows, Mac OS X, GNU/Linux, and other operating systems, the application can be written once and deployed almost anywhere. However, inconsistent implementations of the HTML, CSS , DOM and other browser specifications can cause problems in web application development and support. Additionally, the ability of users to customize many of the display settings of their browser (such as selecting different font sizes, colors, and typefaces, or disabling scripting support) can interfere with consistent implementation of a web application. Another (less common) approach is to use Macromedia Flash or Java Applet s to provide some or all of the user interface. Since most web browsers include support for these technologies (usually through plug-ins), Flash- or Java-based applications can be implemented with much of the same ease of deployment. Because they allow the programmer greater control over the interface, they bypass many browser-configuration issues, although incompabilities between Java or Flash implementations on the client can introduce different complications. Because of their architectural similarities to traditional client-server applications, with a somewhat "thick" client, there is some dispute over whether to call systems of this sort "web applications"; an alternative term is " Rich Internet Application ". STRUCTURE Though many variations are possible, a web application is commonly structured as a Three-tiered application. In its most common form, a web browser is the first tier, an engine using some dynamic web content technology (e.g., CGI , PHP , Java Servlet s or Active Server Pages ) is the middle tier, and a database is the third tier. The web browser sends requests to the middle tier, which services them by making queries and updates against the database and generating a user interface. APPLICATION Web interfaces have increasingly been used for applications that have previously been thought of as traditional, single-user applications. For example, Microsoft HTML Help replaced Windows Help as the primary help system in Microsoft Windows . Like their networked brethren, such applications generate web pages as their user interface and send them (sometimes via an Embedded HTTP Server ) to a local web browser component, which then renders the pages for the user and returns user input to the application. Web applications powered by embedded web servers have also become commonplace as the user interfaces for configuring network components such as servers, switches, routers, and gateways. BUSINESS USE An emerging strategy for application software companies is to provide web access to software previously distributed as local applications. Depending on the type of application, it may require the development of an entirely different browser-based interface, or merely adapting an existing application to use different presentation technology. These programs allow the user to pay a monthly or yearly fee for use of a software application without having to install it on a local hard drive. A company which follows this strategy is known as an Application Service Provider (ASP), and ASPs are currently receiving much attention in the software industry. WRITING WEB APPLICATIONS While many web applications are written directly in PHP or Mod_perl , there are many Web Application Framework s which automate the process, by allowing the programmer to define a higher-level description of the program. The use of web application frameworks can often reduce the number of errors in a program, both by making the code more simple, and by allowing one team to concentrate just on the framework. In applications which are exposed to constant attempts on the Internet, security-related problems caused by errors in the program are a big issue. The OWASP project was developed with the intention of documenting how to avoid security problems in web applications. SEE ALSO
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