PowerPoint PresentationChapter 8 OutlineThe Enhanced Entity-Relationship (EER) ModelSubclasses, Superclasses, and InheritanceSubclasses, Superclasses, and Inheritance (cont’d.)Slide 6Slide 7Specialization and GeneralizationSlide 9Specialization and Generalization (cont’d.)GeneralizationConstraints and Characteristics of Specialization and Generalization HierarchiesConstraints on Specialization and Generalization (cont’d.)Slide 14Specialization and Generalization Hierarchies and LatticesSlide 16Specialization and Generalization Hierarchies and Lattices (cont’d.)Utilizing Specialization and Generalization in Refining Conceptual SchemasModeling of UNION Types Using CategoriesSlide 20A Sample UNIVERSITY EER Schema, Design Choices, and Formal DefinitionsSlide 22Design Choices for Specialization/GeneralizationDesign Choices for Specialization/Generalization (cont’d.)Formal Definitions for the EER Model ConceptsFormal Definitions for the EER Model Concepts (cont’d.)Slide 27SummaryCopyright © 2011 Pearson Education, Inc. Publishing as Pearson Addison-WesleyChapter 8The Enhanced Entity-Relationship (EER) ModelCopyright © 2011 Ramez Elmasri and Shamkant NavatheChapter 8 OutlineSubclasses, Superclasses, and InheritanceSpecialization and GeneralizationConstraints and Characteristics of Specialization and Generalization HierarchiesModeling of UNION Types Using CategoriesA Sample UNIVERSITY EER Schema, Design Choices, and Formal DefinitionsCopyright © 2011 Ramez Elmasri and Shamkant NavatheThe Enhanced Entity-Relationship (EER) ModelEnhanced ER (EER) modelCreated to design more accurate database schemas •Reflect the data properties and constraints more preciselyMore complex requirements than traditional applicationsCopyright © 2011 Ramez Elmasri and Shamkant NavatheSubclasses, Superclasses, and InheritanceEER model includes all modeling concepts of the ER modelIn addition, EER includes:Subclasses and superclassesSpecialization and generalizationCategory or union typeAttribute and relationship inheritanceCopyright © 2011 Ramez Elmasri and Shamkant NavatheSubclasses, Superclasses, and Inheritance (cont’d.)Enhanced ER or EER diagramsDiagrammatic technique for displaying these concepts in an EER schemaSubtype or subclass of an entity typeSubgroupings of entities that are meaningfulRepresented explicitly because of their significance to the database applicationCopyright © 2011 Ramez Elmasri and Shamkant NavatheSubclasses, Superclasses, and Inheritance (cont’d.)Terms for relationship between a superclass and any one of its subclassesSuperclass/subclassSupertype/subtypeClass/subclass relationshipType inheritanceSubclass entity inherits all attributes and relationships of superclassCopyright © 2011 Ramez Elmasri and Shamkant NavatheCopyright © 2011 Ramez Elmasri and Shamkant NavatheSpecialization and GeneralizationSpecialization Process of defining a set of subclasses of an entity typeDefined on the basis of some distinguishing characteristic of the entities in the superclassSubclass can define:Specific attributesSpecific relationship typesCopyright © 2011 Ramez Elmasri and Shamkant NavatheCopyright © 2011 Ramez Elmasri and Shamkant NavatheSpecialization and Generalization (cont’d.)Certain attributes may apply to some but not all entities of the superclassSome relationship types may be participated in only by members of the subclassCopyright © 2011 Ramez Elmasri and Shamkant NavatheGeneralizationReverse process of abstractionGeneralize into a single superclass Original entity types are special subclassesGeneralization Process of defining a generalized entity type from the given entity typesCopyright © 2011 Ramez Elmasri and Shamkant NavatheConstraints and Characteristics of Specialization and Generalization HierarchiesConstraints that apply to a single specialization or a single generalizationDifferences between specialization/generalization lattices and hierarchiesCopyright © 2011 Ramez Elmasri and Shamkant NavatheConstraints on Specialization and Generalization (cont’d.)Disjointness constraintSpecifies that the subclasses of the specialization must be disjointCompleteness (or totalness) constraintMay be total or partialDisjointness and completeness constraints are independentCopyright © 2011 Ramez Elmasri and Shamkant NavatheCopyright © 2011 Ramez Elmasri and Shamkant NavatheSpecialization and Generalization Hierarchiesand LatticesSpecialization hierarchy Every subclass participates as a subclass in only one class/subclass relationshipResults in a tree structure or strict hierarchySpecialization latticeSubclass can be a subclass in more than one class/subclass relationshipCopyright © 2011 Ramez Elmasri and Shamkant NavatheCopyright © 2011 Ramez Elmasri and Shamkant NavatheSpecialization and Generalization Hierarchiesand Lattices (cont’d.)Multiple inheritanceSubclass with more than one superclassIf attribute (or relationship) originating in the same superclass inherited more than once via different paths in lattice•Included only once in shared subclassSingle inheritanceSome models and languages limited to single inheritanceCopyright © 2011 Ramez Elmasri and Shamkant NavatheUtilizing Specialization and Generalization in Refining Conceptual SchemasSpecialization processStart with entity type then define subclasses by successive specializationTop-down conceptual refinement processBottom-up conceptual synthesisInvolves generalization rather than specializationCopyright © 2011 Ramez Elmasri and Shamkant NavatheModeling of UNION Types Using CategoriesUnion type or a categoryRepresents a single superclass/subclass relationship with more than one superclassSubclass represents a collection of objects that is a subset of the UNION of distinct entity typesCategory can be total or partialSome modeling methodologies do not have union typesCopyright © 2011 Ramez Elmasri and Shamkant NavatheCopyright © 2011 Ramez Elmasri and Shamkant NavatheA Sample UNIVERSITY EER Schema, Design Choices, and Formal DefinitionsThe UNIVERSITY Database ExampleUNIVERSITY database •Students and their majors•Transcripts, and registration •University’s course offeringsCopyright © 2011 Ramez Elmasri and Shamkant NavatheCopyright © 2011 Ramez Elmasri and Shamkant NavatheDesign Choices
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