The domain model is a more object-oriented way of indicating the relationships between different objects in the context of the business logic of the application. It is similar to the ER diagram. But instead of merely showing the relationships between the entities involved, it graphically reflects how these entities relate to each other in an object-oriented fashion. On the other hand, an ER diagram is only focused from a relational perspective.

Unified Modeling Language, or UML in short, is a graphical language used to describe object-oriented designs for software systems. UML is quite a vast language, but we will focus more on class diagrams and UML relationships to represent our domain model. Class diagrams are widely used in every object-oriented system to describe the different types of internal relationships between the different business entities.

Before going for a 3-layer object-oriented system, we need to create a domain model of the system. So we need to put...