Chapter 12Chapter 12 - ObjectivesSlide 3Enhanced Entity-Relationship ModelThe Enhanced Entity-Relationship ModelSpecialization / GeneralizationSlide 7Slide 8Slide 9AllStaff Relation Holding Details of all StaffSpecialization/Generalization of Staff Entity into Subclasses Representing Job RolesSpecialization/Generalization of Staff Entity into Job Roles and Contracts of EmploymentEER Diagram with Shared Subclass and Subclass with its own SubclassConstraints on Specialization / GeneralizationConstraints on Specialization / GeneralizationSlide 16DreamHome Worked Example - Staff Superclass with Supervisor and Manager SubclassesDreamHome Worked Example - Owner Superclass with PrivateOwner and BusinessOwner SubclassesDreamHome Worked Example - Person Superclass with Staff, PrivateOwner, and Client SubclassesEER Diagram of Branch View of DreamHome with Specialization/GeneralizationAggregationExamples of AggregationCompositionExample of CompositionChapter 12Enhanced Entity-Relationship ModellingTransparencies2Chapter 12 - ObjectivesLimitations of basic concepts of the ER model and requirements to represent more complex applications using additional data modelling concepts. Most useful additional data modelling concepts of Enhanced ER (EER) model called:–specialization/generalization; –aggregation;–composition.3Chapter 12 - ObjectivesA diagrammatic technique for displaying specialization/generalization, aggregation, and composition in an EER diagram using UML.4Enhanced Entity-Relationship ModelSince 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.5The Enhanced Entity-Relationship ModelSemantic concepts are incorporated into the original ER model and called the Enhanced Entity-Relationship (EER) model.Examples of additional concepts of EER model are:–specialization / generalization;–aggregation;–composition.6Specialization / GeneralizationSuperclass–An entity type that includes one or more distinct subgroupings of its occurrences. Subclass–A distinct subgrouping of occurrences of an entity type.7Specialization / GeneralizationSuperclass/subclass relationship is one-to-one (1:1). Superclass may contain overlapping or distinct subclasses. Not all members of a superclass need be a member of a subclass.8Specialization / GeneralizationAttribute Inheritance–An entity in a subclass represents same ‘real world’ object as in superclass, and may possess subclass-specific attributes, as well as those associated with the superclass.9Specialization / GeneralizationSpecialization –Process of maximizing differences between members of an entity by identifying their distinguishing characteristics. Generalization–Process of minimizing differences between entities by identifying their common characteristics.10AllStaff Relation Holding Details of all Staff11Specialization/Generalization of Staff Entity into Subclasses Representing Job Roles12Specialization/Generalization of Staff Entity into Job Roles and Contracts of Employment13EER Diagram with Shared Subclass and Subclass with its own Subclass14Constraints on Specialization / Generalization Two constraints that may apply to a specialization/generalization: –participation constraints, –disjoint constraints. Participation constraint–Determines whether every member in superclass must participate as a member of a subclass. –May be mandatory or optional.15Constraints on Specialization / GeneralizationDisjoint constraint –Describes relationship between members of the subclasses and indicates whether member of a superclass can be a member of one, or more than one, subclass. –May be disjoint or nondisjoint.16Constraints on Specialization / GeneralizationThere are four categories of constraints of specialization and generalization:–mandatory and disjoint;–optional and disjoint;–mandatory and nondisjoint;–optional and nondisjoint.17DreamHome Worked Example - Staff Superclass with Supervisor and Manager Subclasses18DreamHome Worked Example - Owner Superclass with PrivateOwner and BusinessOwner Subclasses19DreamHome Worked Example - Person Superclass with Staff, PrivateOwner, and Client Subclasses20EER Diagram of Branch View of DreamHome with Specialization/Generalization21Aggregation Represents a ‘has-a’ or ‘is-part-of’ relationship between entity types, where one represents the ‘whole’ and the other ‘the part’.22Examples of Aggregation23CompositionSpecific form of aggregation that represents an association between entities, where there is a strong ownership and coincidental lifetime between the ‘whole’ and the ‘part’.24Example of