Layered architecture is one of the most common architectural patterns. It organizes the codebase into horizontal layers, with each layer addressing one of the following technical concerns: interaction with the consumers, implementing business logic, and persisting the data. You can see this represented in Figure 8-1.

Figure 8-1. Layered architecture

In its classic form, the layered architecture consists of three layers: the presentation layer (PL), the business logic layer (BLL), and the data access layer (DAL).