How class can be used to structure an application

The architecture of a three-tiered application

Description:

Many applications use a three-tiered architecture to separate the application's user interface, business rules, and database processing.
The classes in the presentation layer control the application's user interface. For example: main method, input/output, a GUI application.
The classes in datatabase layer handle all of the application's data processing.
The classes in the middle layer, sometimes calls the business rules layer, act as an interface between the classes in the presentation and database layers.