Special Edition Using Java™ 2 Enterprise Edition

Two-Tiered Applications

Two-tiered designs usually come about because the data layer is complex. If you must perform queries or maintain relationships between data items, you certainly don't want to write that code yourself. Figure 1.3 shows the structure of a typical two-tiered application.

Figure 1.3. A two-tiered design usually puts the data layer into a separate component.

Although the complexity of the data drives an application from single-tiered to two-tiered design, the complexity of the business logic usually drives a two-tiered design into three tiers. If your application is light on business logic or if you are under extreme time pressure, ...