tailieunhanh - Database Systems: Lecture 3 - Nguyen Thanh Tung
Database Systems: Lecture 3 - EER Model presents about Limitations of Basic Concepts of the ER Model, Enhanced-ER (EER) Model Concepts, Subclasses and Superclasses, Specialization and Generalization, Specialization / Generalization Hierarchies, Lattices and Shared Subclasses. | EER Model Outline Limitations of Basic Concepts of the ER Model Enhanced-ER (EER) Model Concepts Subclasses and Superclasses Specialization and Generalization Specialization / Generalization Hierarchies, Lattices and Shared Subclasses Categories Formal Definitions of EER Model Database Design Modeling Tools Reading: [1]: Chapter 4, [2]: Chapter 12 Limitations of Basic Concepts of the ER model Since the 1980s there has been an increase in emergence of new database applications with more demanding requirements Basic concepts of ER modeling are not sufficient to represent requirements of newer, more complex applications Response is development of additional ‘semantic’ modeling concepts Enhanced-ER Model Concepts Includes all modeling concepts of basic ER Additional concepts: subclasses/superclasses, specialization/generalization, categories, attribute inheritance The resulting model is called the Enhanced-ER or Extended ER (E2R or EER) model It is used to model applications . | EER Model Outline Limitations of Basic Concepts of the ER Model Enhanced-ER (EER) Model Concepts Subclasses and Superclasses Specialization and Generalization Specialization / Generalization Hierarchies, Lattices and Shared Subclasses Categories Formal Definitions of EER Model Database Design Modeling Tools Reading: [1]: Chapter 4, [2]: Chapter 12 Limitations of Basic Concepts of the ER model Since the 1980s there has been an increase in emergence of new database applications with more demanding requirements Basic concepts of ER modeling are not sufficient to represent requirements of newer, more complex applications Response is development of additional ‘semantic’ modeling concepts Enhanced-ER Model Concepts Includes all modeling concepts of basic ER Additional concepts: subclasses/superclasses, specialization/generalization, categories, attribute inheritance The resulting model is called the Enhanced-ER or Extended ER (E2R or EER) model It is used to model applications more completely and accurately if needed It includes some object-oriented concepts, such as inheritance Subclasses and Superclasses An entity type may have additional meaningful subgroups of its entities Example: EMPLOYEE may be further grouped into SECRETARY, ENGINEER, MANAGER, TECHNICIAN, SALARIED_EMPLOYEE, HOURLY_EMPLOYEE, Each of these groups is a subset of EMPLOYEE entities Each is called a subclass of EMPLOYEE EMPLOYEE is the superclass for each of these subclasses These are called superclass/subclass relationships Example: EMPLOYEE/SECRETARY, EMPLOYEE/TECHNICIAN EER diagram notation to represent subclasses & specialization Subclasses and Superclasses These are also called IS-A (IS-AN) relationships (SECRETARY IS-A EMPLOYEE, TECHNICIAN IS-A EMPLOYEE, ). Note: An entity that is a member of a subclass represents the same real-world entity as some member of the superclass The Subclass member is the same entity in a distinct specific role An entity cannot exist in the .
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