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The Extended Entity Chapter 5 Relationship Model

1 Chapter 5 Objectives: to learn about the Extended Entity Relationship (E-ER) Model How Entity clusters are used to represent multiple entities and relationships The characteristics of good primary keys and how to select them using flexible solutions for special data modeling cases1CS275 Fall 2010 The Extended Entity Relationship Model Result of adding more semantic constructs to original Entity Relationship (ER) Model Diagram using this Model is called an EER diagram (EERD) Combines some of the Object-oriented concepts with Entity Relationship Fall 2010 Entity Supertypesand Subtypes Entity supertype Generic Entity type related to one or more Entity subtypes Contains common characteristics Entity subtype Contains unique characteristics of each Entity subtype Avoids unnecessary null attributes when not shared by all super Entity Fall 2010 Supertype/Subtype Relationship in an ERD Example of employee (Super type)

The Extended Entity Relationship Model • Result of adding more semantic constructs to original entity relationship (ER) model • Diagram using this model is called an EER diagram (EERD) • Combines some of the Object-oriented concepts with Entity Relationship concepts. 2 Entity Supertypesand Subtypes • Entity supertype –Generic entity ...

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