Extended ER Model (OR EER model)

Why EER model?

Using the ER model for bigger data creates a lot of complexity while designing a database model, So in order to minimize the complexity, we have to enhanced entity-relationship model.

All the components of an ER diagram are included in an EER diagram, with the following additions that help us create and maintain detailed databases through high-level models and tools.

• Specialization
• Generalization
• Aggregation

The below diagram is a representation of an Enhanced Entity-relationship model. As you can see, the below EER model is expanded upon ER models.

---

Sub Class and Super Class

The link between subclasses and superclasses introduces the idea of inheritance. The 'd' symbol is used to indicate the relationship between subclasses and superclasses.

Super Class

A superclass is a type of entity that is connected to one or more subtypes. And, also note that a database entity cannot be created just by belonging to a superclass.

For example: The superclass of shapes includes subgroups like Triangle, Circles, and Squares.

Sub Class

A subclass is a collection of objects with special characteristics. The traits and properties of a subclass are inherited from its superclass.

For example: Triangles, Circles, and squares are the subclass of the Shape superclass.

---

Specialization

Specialization in the ER model is like categorizing entities based on common features.

• A "Supertype" groups entities with shared attributes and relationships, while "Subtypes" have their own unique attributes and relationships. It's a way to organize data efficiently. It is a Top-Down approach.

• We have is-a relationship between superclass and subclass.

Generalization

Generalization is like finding things that are alike and putting them into a big group to represent what they have in common. It helps make things simpler and organized. It is a Bottom-Up approach.

• We have is-a relationship between subclass and superclass.

Inheritance :- It is an important feature of generalization and specialization.

• Attribute inheritance: allows lower level entities to inherit the attributes of higher level entities and vice versa.

• in diagram: Car entity is an inheritance of Vehicle entity ,So Car can acquire attributes of Vehicle example:car can acquire Model attribute of Vehicle.

• Participation inheritance: In participation inheritance, relationships involving higher level entity set also inherited by lower level entity and vice versa.

• in diagram: Vehicle entity has an relationship with Cycle entity ,So Cycle entity can acquire attributes of lower level entities i.e Car and Bus since it is inheritance of Vehicle.

Aggregation

Aggregation is like stacking things on top of each other to create a structure. It is used to create a hierarchical structure in data modeling, showing how a higher-level entity is composed of lower-level entities.

• Abstraction is employed to view relationships from a more general perspective, focusing on a higher-level entity.