Chapter 9 -- Active Server Pages

Chapter 9

More than anything else, the advent of the Internet and intranets has fed the need for server-based applications. The primary motivation for the move to server-based applications is the limited bandwidth available between some of today's clients and servers, especially Internet clients and the servers that feed them. Traditional client/server systems have relied on relatively fat clients, as well as the relatively speedy access to the servers containing the data. When the fat clients could do much of the work of manipulating the data, there was less incentive to create truly scalable server-based applications. The Internet changes all of this.

The earliest Web pages made only modest use of the servers they ran on, merely serving up Hypertext Markup Language (HTML) pages to relatively primitive Web browsers. For a long time, this was enough. Even today, many Web sites simply provide static documents and perhaps a modest search capabilityfor example, sites that allow searches of archives of medical and scientific information.

As time progressed, however, Web sites began to transform into Web applications. A Web application is distinguished by the fact that the content provided is not simply a set of static Web pages, though there might be some static content included. A Web application presents dynamic content to the user and, more often than not, allows the user to interact with the database behind the dynamic content. This moves the Web application beyond animated icons and musical pages.

There are several alternatives to consider for creating Web applications. The first method, used primarily on UNIX Web servers, is Common Gateway Interface (CGI). I discussed CGI briefly in Chapter 3, so I won't dwell on it here, but in general, CGI provides a way to use existing programming tools to create applications that use the standard input of a program to get information from the user of the browser and send information back to the browser using standard output. CGI programs can therefore be written in languages that UNIX users are comfortable with, including C and scripted languages like Perl.

CGI has a dark side, however. Each time it is called, a CGI program creates a new process for each user. Process creation is a relatively expensive operation, and thus limits the scalability of these Web applications. In the Microsoft Windows NT world, these CGI applications never really caught on, primarily because of the inclusion of Microsoft Internet Information Server (IIS) with Windows NT and, later, Windows 2000. IIS offers several alternatives to CGI applications. Some of these optionswhich I'll discuss in later chaptersmake use of the Internet Server API (ISAPI). One of the most popular alternatives offered by IIS is Active Server Pages (ASP).