Client/Server Unchained: Finally, Hardware Independence: Page 2

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Federated's Five Layers Make Client/Server Work

When you start trying to develop complex C/S apps, you first have to develop a series of tactics to keep it all under control. David Guzman, information systems manager at the Federated Systems Group, a wholly owned subsidiary of Federated Department Stores in Atlanta, developed the following five layering standards for developers to follow as part of the multitier development process.

Says Guzman, "It's really important that the application itself is designed from the start to take advantage of the multitier architecture. To do that, you've got to develop a set of application-layering standards. In our case, we have five layers in our application architecture."

First, Federated separates out the application presentation layer--where they develop components such as smooth-scrolling logic and data-formatting logic.

Second is the event coordination layer-where they put the basic "if then, else" conditional logic and case state logic--the event-driven logic that checks which buttons on the GUI a user selects and then decides what actions to take as the result of that selection.

Third is the application process layer. That's where all the hard-core business logic takes place. When a certain event or case takes place in the event coordination layer, the process layer decides exactly what code to call from a business perspective.

Fourth comes the data abstraction layer. This is the logical view that the process logic gets of the data attached to the application.

And fifth is the physical data access layer--where the whole application is tied to a particular DBMS.

"During this whole process," says Guzman, "you can't concern yourself with the physical partitioning of the application or with its location, network-operating system, or even its overall application environment. You've just got to focus on the application logic itself."



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