26.1. System Architecture

Most distributed architectures discuss three tiers in the development of Web-based applications, but the Web Server tier should really be thought of as a separate layer. In fact, as we move closer and closer to Web services this layer might be replaced altogether. Therefore, the layers modeled for the CRSS are:

  • Client tier

  • Web Server tier

  • Application tier

  • Database tier

Let’s look at each tier and the technologies used today. The Client tier typically consists of HTML and JavaScript for computers and Wireless Markup Language (WML) for PDAs. It is possible to embed many other controls (Shockwave, applets, ActiveX), but we will exclude these plug-in technologies from our application.

The simplest way to model the application ...

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