Structure of Web Applications

Though there are as many variations as possible, a Web application is commonly structured as a three-tiered application. The Web browser, in its most common form, is the first tier. The second tier or the middle tier is an engine using some dynamic Web content technology. Some of these are ASP, ASP.NET, CGI, ColdFusion, JSP/Java, PHP,embPerl, Python, or Ruby on Rails. The third tier is a database. The Web browser, which is the first tier, sends requests to the middle tier, which then services them by making queries and updating against the database then generating a user interface.