The layered architecture style, also known as n-tiered, is one of the most common architecture styles. It’s the de facto standard for many legacy applications because of its simplicity, familiarity, and low cost.
The layered architecture style can fall into several architectural antipatterns, including the Architecture by Implication and the Accidental Architecture antipatterns. When developers or architects “just start coding,” unsure which architecture style they are using, chances are good that they’re implementing the layered architecture style.
Topology
Components within the layered architecture style are organized into logical horizontal layers, as shown in Figure 10-1, with each layer performing a specific role within the application (such as presentation logic or business logic). Although there are no specific restrictions in terms of the number and types of layers that must exist, most layered architectures consist of four standard layers: Presentation, Business, Persistence, and Database. Some architectures combine the Business and Persistence layers, particularly when the persistence logic (such as SQL or HSQL) is embedded within the Business layer components. Smaller applications may have only three layers, whereas larger and more complex business applications may contain five or more.
Figure 10-1. Standard logical layers within ...
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