Extended Entity-Relationship (EE-R) Model

The Extended Entity-Relationship (EE-R) Model is a high-level data model that incorporates extensions to the original ER model to represent complex database requirements. In addition to basic ER concepts, EE-R includes −

• Subclasses and Super classes
• Specialization and Generalization
• Category or Union type
• Aggregation

Subclasses and Super Class

A super class contains common attributes shared by all its subtypes. Sub classes are groups of entities with unique attributes that inherit properties from the super class ?

Specialization and Generalization

Generalization is a bottom-up process of combining sub-entities into a generalized super class. Specialization is a top-down process of dividing a super class into specialized sub-entities ?

Car, Truck, and Motorcycle can be generalized into Vehicle (bottom-up). Conversely, Vehicle can be specialized into Car, Truck, or Motorcycle (top-down).

Category or Union

A category represents a subclass related to more than one super class, modeling union types ?

Owner can inherit from either Vehicle or House, representing that an owner can own vehicles, houses, or both.

Aggregation

Aggregation treats a relationship set as a higher-level entity for participating in another relationship ?

The Works_On relationship between Employee and Project is treated as a higher-level entity, allowing Manager to have a "Manages" relationship with the aggregated Works_On set.

Conclusion

The EE-R model extends basic ER with subclass/superclass hierarchies, specialization/generalization, union types, and aggregation. These constructs enable modeling of complex real-world scenarios like inheritance, multiple super classes, and relationships between relationships that basic ER cannot adequately represent.