Shamkant B Navathe Extended EntityRelationship EER Model l
© Shamkant B. Navathe
Extended Entity-Relationship (EER) Model l Subclasses, Superclasses, Inheritance l Specialization and generalization l Constraints and characteristics of specialization and generalization l Hierarchies and lattices Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Elmasri and Navathe. 2
Specialization l Specialization: – The process of defining a set of subclasses of an entity type – The entity type is the superclass of the specialization – The set of subclasses form a specialization. – Subclasses have their own specific attributes and relationships, and inherit all the attributes and relationships from the superclass. Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Elmasri and Navathe. 3
Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Elmasri and Navathe. 4
Generalization l Generalization – The process of generalizing several entity types by grouping them based on their common features – The inverse of the specialization process Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Elmasri and Navathe. 5
Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Elmasri and Navathe. 6
Refining Conceptual Schema l Successive specialization – Top-down conceptual refinement process l Successive generalization – Bottom-up conceptual synthesis Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Elmasri and Navathe. 7
Constraints, Characteristics l Defining attributes and defining predicates l Constraints – Disjointness: overlapping (o) and disjoint (d) – Completeness: total and partial specialization Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Elmasri and Navathe. 8
Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Elmasri and Navathe. 9
Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Elmasri and Navathe. 10
Lattices l Specialization lattices – A subclass can be in more than one class/subclass relationships. – A subclass with more than one superclasses is called a shared subclass. – Multiple inheritance: shared subclass inherits attributes and relationships from its superclasses. Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Elmasri and Navathe. 11
Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Elmasri and Navathe. 12
Figure 4. 7 A specialization lattice (with multiple inheritance) for a UNIVERSITY database. Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition Copyright © 2004 Elmasri and Navathe. 13
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