Developing Web Applications

The Middle Tier

This section discusses what is perhaps the most important layer of Web programming, the middle tier. It is here that user input is combined with business logic to perform the work of your site.

The middle tier is not always just a single layer of logic. It can consist of many interrelated technologies, seamlessly combined to create the illusion of a single multipurpose layer. For example, the client’s request could be preprocessed by an Internet Server Application Programming Interface (ISAPI) filter, then execute a script to run a custom-built component that manipulates a database with ADO. Technology integrates with technology, layer upon layer: a demonstration of true n-tier architecture.

Middle-tier technologies discussed in this section include CGI (Common Gateway Interface) applications, ISAPI extensions and filters, ASP, process isolation and crash recovery, and others.

See the following:

• CGI Applications
• ISAPI Extensions and Filters
• Active Server Pages
• ASP Applications
• Process Isolation and Crash Recovery
• A Note About Application Testing

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