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UT Dallas CS 6360 - Ch08

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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 GeneralizationConstraints on Specialization and Generalization (cont’d.)Slide 15Specialization and Generalization Hierarchies and LatticesSlide 17Specialization and Generalization Hierarchies and Lattices (cont’d.)Utilizing Specialization and Generalization in Refining Conceptual SchemasModeling of UNION Types Using CategoriesA 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 27Example of Other NotationSlide 29Data Abstraction, Knowledge Representation, and Ontology ConceptsClassification and InstantiationClassification and Instantiation (cont’d.)IdentificationSlide 34Aggregation and AssociationSlide 36Slide 37Ontologies and the Semantic WebSummaryCopyright © 2011 Pearson Education, Inc. Publishing as Pearson Addison-WesleyChapter 8The Enhanced Entity-Relationship (EER) ModelCopyright © 2011 Ramez Elmasri and Shamkant NavatheChapter 8 OutlineSubclasses, Superclasses, and InheritanceSpecialization and GeneralizationConstraints and Characteristics of Specialization and Generalization HierarchiesModeling of UNION Types Using CategoriesA Sample UNIVERSITY EER Schema, Design Choices, and Formal DefinitionsCopyright © 2011 Ramez Elmasri and Shamkant NavatheThe 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 applicationsCopyright © 2011 Ramez Elmasri and Shamkant NavatheSubclasses, 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 inheritanceCopyright © 2011 Ramez Elmasri and Shamkant NavatheSubclasses, 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Subgroupings of entities that are meaningfulRepresented 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 subclassesSuperclass/subclassSupertype/subtypeClass/subclass relationshipType inheritanceSubclass entity inherits all attributes and relationships of superclassCopyright © 2011 Ramez Elmasri and Shamkant NavatheCopyright © 2011 Ramez Elmasri and Shamkant NavatheSpecialization 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 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 superclassSome relationship types may be participated in only by members of the subclassCopyright © 2011 Ramez Elmasri and Shamkant NavatheGeneralizationReverse process of abstractionGeneralize into a single superclass Original entity types are special subclassesGeneralization Process of defining a generalized entity type from the given entity typesCopyright © 2011 Ramez Elmasri and Shamkant NavatheConstraints and Characteristics of Specialization and Generalization HierarchiesConstraints that apply to a single specialization or a single generalizationDifferences between specialization/generalization lattices and hierarchiesCopyright © 2011 Ramez Elmasri and Shamkant NavatheConstraints on Specialization and GeneralizationMay be several or one subclassDetermine entity subtype:Predicate-defined (or condition-defined) subclassesAttribute-defined specializationUser-definedCopyright © 2011 Ramez Elmasri and Shamkant NavatheConstraints on Specialization and Generalization (cont’d.)Disjointness constraintSpecifies that the subclasses of the specialization must be disjointCompleteness (or totalness) constraintMay be total or partialDisjointness and completeness constraints are independentCopyright © 2011 Ramez Elmasri and Shamkant NavatheCopyright © 2011 Ramez Elmasri and Shamkant NavatheSpecialization and Generalization Hierarchiesand 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 relationshipCopyright © 2011 Ramez Elmasri and Shamkant NavatheCopyright © 2011 Ramez Elmasri and Shamkant NavatheSpecialization and Generalization Hierarchiesand 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 inheritanceCopyright © 2011 Ramez Elmasri and Shamkant NavatheUtilizing Specialization and Generalization in Refining Conceptual SchemasSpecialization processStart with entity type then define subclasses by successive specializationTop-down conceptual refinement processBottom-up conceptual synthesisInvolves generalization rather than specializationCopyright © 2011 Ramez Elmasri and Shamkant NavatheModeling of UNION Types Using CategoriesUnion type or a categoryRepresents a single superclass/subclass relationship with more than one superclassSubclass represents a collection of objects that is a


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UT Dallas CS 6360 - Ch08

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