Web Application Development: How a Web Application Works

A web application is a collection of regular and dynamic web pages. A regular web page is one that does not change when a user requests it: the web server sends the page to the requesting web browser without modifying it. In contrast, a dynamic web page is modified by the server before it is sent to the requesting browser. The changing nature of the page is why it’s called dynamic.



For example, you could design a page to display fitness results and leave certain information (such as employee name and results) to be determined when the page is requested by an employee.

To build web applications you need the following:

An application server that runs on your web server, or a web server that doubles as an application server, such as Microsoft PWS or IIS
Note: In the context of web applications, the terms “web server” and “application server” refer to software, not hardware.

If you want to use a database with your application, you need the following additional software:

A database or database system
A database driver that supports your database

Web Servers
A web server is software that serves files in response to requests from web browsers. A web server is sometimes called an HTTP server. Common web servers include IIS, Netscape Enterprise Server, iPlanet Web Server, and Apache HTTP Server.

Several web hosting companies offer plans that let you use their software to test and deploy web applications. If you’re a Windows user, you can install the required software on the same computer as you use for development purposes. You can also install the software on a network computer (typically a Windows NT or Windows 2000 computer) so that other developers on your team can work on a project.

If you’re a Macintosh user, you can use a web hosting service or install the required software on a remote computer. If you’re a Mac OS 10.1 user, you can develop PHP sites locally using the Apache web server and PHP application server installed with your operating system.

If you’re not using a web hosting service, choose a web server and install it on your local computer or on a remote computer. For more information, see the server vendor’s documentation or your system administrator.

Windows users can get a web server up and running quickly on their local computer by installing either PWS or IIS. The web server may already be installed. Check your folder structure to see if it contains a C:\Inetpub or D:\Inetpub folder. PWS and IIS create this folder during installation. If you want to install PWS or IIS, see Installing a Web Server in Windows.

ASP.NET pages only work with one web server: Microsoft IIS 5 or higher. PWS is not supported. Also, because IIS 5 is a service of the Windows 2000 and Windows XP Professional operating systems, you can only use these two versions of Windows to run ASP.NET applications. Windows 98, ME, or NT are not supported.

Application Servers
An application server is software that helps a web server process web pages containing server-side scripts or tags. For example, if you have the ColdFusion MX, you can choose ColdFusion as your server technology. If you have access to a server running Microsoft Internet Information Server 5 (IIS) with the .NET Framework, you can choose ASP.NET. PHP is an option if you have access to a web server with a PHP application server; JSP is an option if you have access to a web server with a JSP application server (such as Macromedia JRun).

Your choice of application server depends on several factors, including your budget, the server technology you want to use (ColdFusion, ASP.NET, ASP, JSP, or PHP), and your choice of web server.

Budget: Some vendors sell high-end application servers that are expensive to buy and administer. Others vendors provide easier, more cost-effective solutions (examples include Macromedia ColdFusion and JRun servers). Some application servers are built into web servers (such as Microsoft IIS and PWS) and others can be downloaded for free from the Internet (such as Jakarta Tomcat and PHP).

Server technology: Application servers use different technologies, such as ColdFusion, ASP.NET, ASP, JSP, and PHP. The following table shows common application servers available for the five server technologies listed.