Question

Database Design

In the EER modeling process, what does inheritance mean? Give one specific example of it.

Answer 1

EER is a high-level data model that incorporates the extensions to the original ER model.
EER is a diagrammatic technique for displaying the following concepts. It includes the concept of specialization and generalization. It is used to represent a collection of objects that is union of objects of different of different entity types.

By inheritance in EER modelling means representing the relationships between different entities that are seperated to achieve specialization and generalization.

the entity which is commob to more then 1 entity can be seperated to form a common repationship with other repated entities.

e.g. an Employee can be Part_Time or Full_Time or a person can be Employee or a Customer . In ERR modeling the leading entities are called as Super Claass and all the related entities are called as Sub Class

Sub Class and Super Class

Sub class and Super class relationship express the concept of Inheritance. The relationship between sub class and super class is denoted with 'd' symbol.

Super class is an entity type that has a relationship with one or more subtypes.An entity cannot exist in database merely by being member of any super class.

Sub class is a group of entities with unique attributes.Sub class inherits properties and attributes from its super class.

The process of using inheritance is categorized as Specialization and Generalization

Specialization

Specialization is a process that defines a group of entities which is divided into sub groups based on their characteristic. It is a top down approach, in which one higher entity can be broken down into two or more lower level entity. It maximizes the difference between the members of an entity by identifying the unique characteristic or attributes of each member. It defines one or more sub class for the super class and also forms the superclass/subclass relationship.

Generalization

Generalization is the process of generalizing the entities which contain the properties of all the generalized entities.It is a bottom approach, in which two or more lower level entities combine to form a higher level entity.Generalization is the reverse process of Specialization and it minimizes the difference between the entities by identifying the common features.