The paper "Database Abstractions: Aggregation and Generalization" by John Miles Smith and Diane C.P. Smith from the University of Utah introduces two fundamental abstractions in database design: aggregation and generalization. Aggregation turns a relationship between objects into an aggregate object, while generalization turns a class of objects into a generic object. The authors propose a new data type called "generic" to facilitate the modeling of these abstractions. They develop a structured approach using aggregation hierarchies and generalization hierarchies, where abstract objects occur at their intersections. This structure provides benefits such as integrated and maintained views, stability under evolutionary changes, easier understanding of complex models, systematic database design, and more efficient implementation. The generic type is formalized by a set of invariant properties, and a mechanism is proposed to automatically maintain these invariants during update operations. The paper also discusses the representation of generalization abstractions in Codd's relational schema and provides a graphical notation for modeling real-world scenarios. The authors illustrate how to use aggregation and generalization to model various aspects of the real world, including employee types, trade unions, and project assignments. They also detail the maintenance of relational invariants during update operations to ensure the integrity of the database model.The paper "Database Abstractions: Aggregation and Generalization" by John Miles Smith and Diane C.P. Smith from the University of Utah introduces two fundamental abstractions in database design: aggregation and generalization. Aggregation turns a relationship between objects into an aggregate object, while generalization turns a class of objects into a generic object. The authors propose a new data type called "generic" to facilitate the modeling of these abstractions. They develop a structured approach using aggregation hierarchies and generalization hierarchies, where abstract objects occur at their intersections. This structure provides benefits such as integrated and maintained views, stability under evolutionary changes, easier understanding of complex models, systematic database design, and more efficient implementation. The generic type is formalized by a set of invariant properties, and a mechanism is proposed to automatically maintain these invariants during update operations. The paper also discusses the representation of generalization abstractions in Codd's relational schema and provides a graphical notation for modeling real-world scenarios. The authors illustrate how to use aggregation and generalization to model various aspects of the real world, including employee types, trade unions, and project assignments. They also detail the maintenance of relational invariants during update operations to ensure the integrity of the database model.