Chap3-Entity Relationship (E-R) Modeling

Chap3-Entity Relationship (E-R) Modeling - Entity...

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Unformatted text preview: Entity Relationship (E-R) Modeling 2 Objectives How internal and external models serve the database design process? Relationships between entities are defined and refined, and how such relationships are incorporated into the database design process Effect of ERD components on database design and implementation 3 Interpret the modeling symbols for the four most popular E-R modeling tools 4 Basic Modeling Concepts Models Description or analogy used to visualize something that cannot be directly observed Websters Dictionary Data Model Relatively simple representation of complex real-world data structures 5 The Entity Relationship (E-R) Model Represents conceptual view Main Components Entities Corresponds to entire table, not row Represented by rectangle Attributes Relationships 6 Attributes Characteristics of entities Domain is set of possible values Primary keys underlined 7 Attributes (cont.) Simple Cannot be subdivided Age, marital status Composite Can be subdivided into additional attributes Address into street, city, zip Single-valued Can have only a single value Person has one social security number Multi-valued Can have many values Person may have several college degrees Derived Can be derived with algorithm Age can be derived from date of birth 8 Relationships Association between entities...
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Chap3-Entity Relationship (E-R) Modeling - Entity...

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