How classes can be used to structure an application

• To simplify development and maintenance, many applications use a three-tiered architecture to separate the application's user interface, business rules, and database processing.
• Classes are used to implement the functions performed at each layer of the architecture.
• The classes in the presentation layer control the application's user interface.
• The classes in the database layer handle all of the application's data processing.
• The classes in the middle layer, which is sometimes called the business rules layer, act as an interface between the classes in the presentation and database layers. The objects created from these business classes are called business objects.