The web architecture is another step in evolution that appears to be only slightly different from the distributed application architecture. It makes a true ultra-thin client possible by providing only display information in the form of HTML to a client. All controller logic occurs in a new component, the web server. Figure 8-4 illustrates the web architecture.

Figure 8-4. The web application architecture

The controller comes in many different forms, depending on the technologies you are using. PHP, CGI, JSP, ASP, ColdFusion, and WebObjects are all examples of technologies for processing user events. Some of these technologies even divide things further into content creation and controller logic. If you use a content management system such as OpenMarket, for example, your JSP is nothing more than a tool for dynamically building your HTML. The actual controller logic is passed off to a servlet action handler that performs any application server interaction.

The focus of this book will be the web architecture since it is the most common architecture in which MySQL is used. We will use both the vision of the web architecture shown in Figure 8-4 and a simpler one in which the application logic is embedded with controller logic in the web server. The simpler architecture is mostly relevant to MySQL applications since MySQL performs best for heavy read applications—applications without complex application logic.