In software engineering, a web application is an application delivered to users from a web server over a network such as the World Wide Web or an intranet. Web applications are popular due to the ubiquity of the web browser as a client, sometimes called a thin client. The ability to update and maintain web applications without distributing and installing software on potentially thousands of clients is another reason they are popular. Applications like webmail, Amazon.com and eBay are well known examples of web applications but they have uses in many other areas of business and science.

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 created using some dynamic web content technology (e.g., CGI, PHP, Java Servlets 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.

In recent times, there has been an increased tendency to include web interfaces for applications that usually have been thought of as traditional, single user applications. With the expansion of home networks, more applications realize there is an increased utility for thin-client interfaces and even replace traditional GUIs where possible, using an embedded HTTP server.

An emerging strategy for application software companies is to provide web access to software that has heretofore been distributed as local applications. 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.

See also

• AJAX
• Cascading Style Sheets
• HTML and XHTML
• LAMP: Linux, Apache, MySQL and Perl/Python/PHP
• Microsoft .NET
• REST
• Rich Internet Application
• Web service
• Website
• World Wide Web Consortium (web standards)
• XML

External links

• How Microsoft lost the API war — A discussion on how web applications are replacing windows applications
• The Other Road Ahead — An article arguing that the future lies on the server, not rich interfaces on the client