In object-oriented programming and database design, a class hierarchy refers to a structure that organizes classes in a tree-like hierarchical structure, where each class is a child of a parent class, and each parent class can have multiple child classes. The parent class in this hierarchy is referred to as a superclass or base class, and the child classes are referred to as subclasses or derived classes.
In database design, a class hierarchy can be represented in an ER diagram using the 'Generalization/Specialization' feature, also known as the 'Is-A' relationship. This feature allows the modeling of a superclass and its subclasses in a tree-like structure, where the superclass is at the top and the subclasses are at the bottom.
In an ER diagram, the superclass is represented as an entity set, and the subclasses are represented as subtypes of the superclass, which are connected to the superclass using a line with a triangle pointing to the superclass. The subtypes can have their attributes, as well as attributes inherited from the superclass.
For example, consider a scenario where we have a class hierarchy of vehicles, where the superclass is 'Vehicle,' and the subclasses are 'Car,' 'Truck,' and 'Motorcycle.' In an ER diagram, the superclass 'Vehicle' is represented as an entity set, and the subclasses 'Car,' 'Truck,' and 'Motorcycle' are represented as subtypes connected to the superclass using a line with a triangle pointing to the superclass. Each subtype can have its attributes, as well as attributes inherited from the superclass 'Vehicle,' such as 'make,' 'model,' 'year,' 'color,' and 'weight.'
In summary, the class hierarchy is a structure that organizes classes in a tree-like hierarchical structure, and it can be represented in an ER diagram using the 'Generalization/Specialization' feature, which allows the modeling of a superclass and its subclasses in a tree-like structure.
