chapter5 - The Extended Entity Relationship Model Result of...

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Chapter 5 Advanced Data Modeling BUS 173 Winter 2011 Dr. Hamouda 2 The Extended Entity Relationship Model Result of adding more semantic constructs to original entity relationship (ER) model entity types arranged in a hierarchical structure to show similarity in attributes Examples: Group employees based on their salaries, rank,… Group university employees (faculty, staff, students) Group investments (bonds, stocks,…) Diagram using this model is called an Extended Entity Relationship Diagram (EERD) Example : Consider an airline company where employee information is maintained in an EMPLOYEE table Employees = accountants, fight attendants, pilots, mechanics,… The Extended Entity Relationship Model Attributes relevant to pilots only EMPLOYEE EMP_NUM EMP_LNAME EMP_FNAME EMP_INITIAL EMP_HIRE_DATE PILOT EMP_LICENSE EMP_RATINGS EMP_MED_TYPE 4 Entity Supertypes and Subtypes Entity supertype (parent entity) Generic entity type related to one or more entity subtypes Contains common characteristics Entity subtype (child entity) Contains unique characteristics of each entity subtype EMPLOYEE EMP_NUM EMP_LNAME EMP_FNAME EMP_INITIAL EMP_HIRE_DATE PILOT EMP_LICENSE EMP_RATINGS EMP_MED_TYPE 5 Specialization Hierarchy Entity supertypes and subtypes are organized in a specialization hierarchy which
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chapter5 - The Extended Entity Relationship Model Result of...

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