EER - Enhanced Entity Relation Model EER stands for...

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Enhanced Entity Relation Model b EER stands for Enhanced ER or Extended ER b EER Model Concepts b Includes all modeling concepts of basic ER b Additional concepts: b subclasses/superclasses b specialization/generalization b attribute and relationship inheritance b These are fundamental to conceptual modeling b The additional EER concepts are used to model applications more completely and more accurately b EER includes some object-oriented concepts, such inheritance
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Subclasses and Superclasses b An entity type may have additional meaningful subgroupings of its entities b Example: EMPLOYEE may be further grouped into: SECRETARY, ENGINEER, TECHNICIAN, … Based on the EMPLOYEE’s Job MANAGER EMPLOYEEs who are managers SALARIED_EMPLOYEE, HOURLY_EMPLOYEE Based on the EMPLOYEE’s method of pay b Each of these subgroupings is a subset of EMPLOYEE entities. b Each of these subgroupings is called a subclass of EMPLOYEE b EMPLOYEE is the superclass for each of these subclasses
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Subclasses and Superclasses b These are called superclass/subclass relationships: EMPLOYEE/SECRETARY EMPLOYEE/TECHNICIAN EMPLOYEE/MANAGER b EER diagrams extend ER diagrams to represent these additional subgroupings, called subclasses or subtypes b The subclass that define a specialization are attached by lines to the circle which is connected to the superclass.
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b These are also called IS-A relationships (PERSON IS-A EMPLOYEE, PERSON IS-A CUSTOMER,. ..) b Note: An entity that is member of a subclass represents the same real world entity as some member of the superclass s The Subclass member is the same entity in a distinct specific role s An entity cannot exist in the database merely by being a member of a subclass; it must also be a member of the superclass. s
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This note was uploaded on 04/01/2012 for the course CSE,IT 101 taught by Professor Mirunaalini during the Spring '12 term at Indian Institute of Technology, Chennai.

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EER - Enhanced Entity Relation Model EER stands for...

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