Chapter 8 The Enhanced Entity Relationship EER Model CS 6360 Database Design Chris Irwin Davis Ph D Email cid021000 utdallas edu Phone 972 883 3574 O ce ECSS 4 705 Chapter 8 Outline 8 1 Subclasses Superclasses and Inheritance 8 2 Specialization and Generalization 8 3 Constraints and Characteristics of Specialization and Generalization Hierarchies 8 4 Modeling of UNION Types Using Categories 2 The Enhanced Entity Relationship EER Model Enhanced ER EER model Created to design more accurate database schemas Reflect the data properties and constraints more precisely More complex requirements than traditional applications 3 Subclasses Superclasses and Inheritance EER model includes all modeling concepts of the ER model In addition EER includes Subclasses and superclasses Specialization and generalization Category or union type Attribute and relationship inheritance 4 8 1 Subclasses Superclasses and Inheritance Subclasses Superclasses and Inheritance cont d Enhanced ER or EER diagrams Diagrammatic technique for displaying these concepts in an EER schema Subtype or subclass of an entity type Sub groupings of entities that are meaningful Represented explicitly because of their significance to the database application 6 Subclasses Superclasses and Inheritance cont d Terms for relationship between a superclass and any one of its subclasses Superclass subclass Supertype subtype Class subclass relationship Type inheritance Subclass entity inherits all attributes and relationships of superclass 7 Subclass and Specialization 8 8 2 Specialization and Generalization Specialization and Generalization Specialization Process of defining a set of subclasses of an entity type Defined on the basis of some distinguishing characteristic of the entities in the superclass Subclass can define Specific attributes Specific relationship types 10 11 Specialization and Generalization cont d Two main reasons for including class subclass relationships and specializations in a data model Certain attributes may apply to some but not all entities of the superclass Some relationship types may be participated in only by members of the subclass 12 Generalization Reverse process of specialization which is abstraction Generalize into a single superclass Original entity types are special subclasses Generalization Process of defining a generalized entity type from the given entity types 13 Generalization Example 14 Generalization Example 15 8 3 Constraints and Characteristics of Specialization and Generalization Hierarchies Constraints and Characteristics of Specialization and Generalization Hierarchies Constraints that apply to a single specialization or a single generalization How to deal with Differences between specialization generalization lattices and hierarchies Continued 17 Constraints on Specialization and Generalization May be several or one subclass How to determine entity subtype Predicate defined or condition defined subclasses 18 Constraints on Specialization and Generalization May be several or one subclass Determine entity subtype Predicate defined or condition defined subclasses Predicate defined subclass are displayed by writing the predicate condition next to the line that connects the subclass to the specialization circle 19 Constraints on Specialization and Generalization May be several or one subclass Determine entity subtype Predicate defined or condition defined subclasses Attribute defined specialization 20 Constraints on Specialization and Generalization May be several or one subclass Determine entity subtype Predicate defined or condition defined subclasses Attribute defined specialization 21 Constraints on Specialization and Generalization May be several or one subclass Determine entity subtype Predicate defined or condition defined subclasses Attribute defined specialization User defined 22 Constraints on Specialization and Generalization cont d Disjointness constraint Specifies that the subclasses of the specialization must be disjoint 23 Constraints on Specialization and Generalization cont d Disjointness constraint Specifies that the subclasses of the specialization must be disjoint 24 Constraints on Specialization and Generalization cont d Disjointness constraint Specifies that the subclasses of the specialization must be disjoint disjoint overlap 25 Constraints on Specialization and Generalization cont d Completeness or totalness constraint for subtype May be total or partial Disjointness and completeness constraints are independent 26 Constraints on Specialization and Generalization cont d Completeness or totalness constraint May be total or partial Disjointness and completeness constraints are independent total participation 27 Specialization and Generalization Hierarchies and Lattices Specialization hierarchy Every subclass participates as a subclass in only one class subclass relationship Results in a tree structure or strict hierarchy Specialization lattice Subclass can be a subclass in more than one class subclass relationship i e multiple inheritance 28 Specialization and Generalization Hierarchies and Lattices partial total 29 Specialization Lattice w Multiple Inheritance 30 Specialization and Generalization Hierarchies and Lattices cont d Multiple inheritance Subclass with more than one superclass If attribute or relationship originating in the same superclass inherited more than once via different paths in lattice Included only once in shared subclass Single inheritance Some models and languages limited to single inheritance 31 Specialization Lattice w Multiple Inheritance 32 Utilizing Specialization and Generalization in Refining Conceptual Schemas Specialization process Top down conceptual refinement process Start with entity type then define subclasses by successive specialization Generalization process Bottom up conceptual synthesis Involves generalization rather than specialization 33 Modeling of UNION Types Using Categories Union type or a category Represents a single superclass subclass relationship with more than one superclass disjoint not overlap Subclass represents a collection of objects that is a subset of the UNION of distinct entity types Attribute inheritance works more selectively Category can be total or partial Some modeling methodologies do not have union types 34 Modeling of UNION Types Using Categories 35 A Sample UNIVERSITY EER Schema Design Choices and Formal Definitions The UNIVERSITY Database Example Students and their majors Transcripts and
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