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Explain Specialization and Generalization in E-R diagram with example.
- Explain Specialization and Generalization in E-R diagram with example.
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For all practical purposes generalization and specialization is inversion of each other Specialization A top down design process that creates subclasses based on some different characteristics of the entities in the superclass An entity set may include sub groupings of entities that are distinct in some way from other entities in the set For example a subset of entities within an entity set may have attributes that are not shared by all the entities in the entity set Consider an entity set person with attributes name street and city A person may be further classified as one of the following customer Employee For example customer entities may be described further by the attribute customerid creditrating and employee entities may be described further by the attributes employeeid and salary The process of designating sub groupings within an entity set is called specialization The specialization of person allows us to distinguish among persons according to whether they are employees or customers Now again employees may be further classified as one of the following officer teller secretary Each of these employee types is described by a set of attributes that includes all the attributes of entity set employee plus additional attributes For example officer entities may be described further by the attribute officenumber teller entities by the attributes stationnumber and hoursperweek and secretary entities by the attribute hoursperweek In terms of an ER diagram specialization is depicted by a triangle component labeled ISA The label ISA stands for is a and represents for example that a customer is aperson The ISA relationship may also be referred to as a superclass subclass ...
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Data Modeling and Database Design
Authors: Narayan S. Umanath, Richard W. Scammel
2nd edition
1285085256, 978-1285085258
