In this chapter, we looked at multi-tier development as a way to develop web sites and applications. The whole idea around multi-tier development is to abstract the data (content), logic, and presentation layers to minimize the interaction between layers. When developing multi-tier applications, the focus should be on design and not on coding. Scalability and performance are fundamentally tied to the way you design and architect your application. The use of OOP and abstraction classes is the key to a successful multi-tiered architecture.
We explored several alternatives for the data layer – plain files, relational database, XML, and hybrid models. It is important to make sure that the data layer is isolated from the other layers using abstraction classes and APIs, so that it is possible to change the entire data layer without changing the programs using it. We explored the logic layer and the presentation layer, and we also looked into a common HTML based multi-tiered architecture, and a brand new approach using XML.