Chapter 3 The Entity-Relationship Model David M. Kroenke Database Processing © 2000 Prentice Hall.

Chapter 3The Entity-Relationship Model

David M. Kroenke

Database Processing

© 2000 Prentice Hall

Chapter 3

© 2000 Prentice Hall

Data Modeling

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• Process of creating a logical representation of the structure of the database

• The most important task in database development

Chapter 3

© 2000 Prentice Hall

Entity-Relationship Model

• E-R Model• Peter Chen, 1976

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Entities“something that users track”

Page 49Figure 3-1 © 2000 Prentice Hall

Chapter 3

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Attributes (properties)

“describe the entity’s characteristics”

Entity: EmployeeAttributes:EmployeeName, Extension,

DateOfHire, JobSkillCode

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Chapter 3

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Identifier

“attributes that name entity instances”

Entity: EmployeeIdentifier:SocialSecurityNumber

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Relationships“associations between entities”

Page 51Figure 3-3 © 2000 Prentice Hall

Cardinality

“maximum or minimum number of entities that can occur on one side of a relationship”

Page 52Figure 3-4 © 2000 Prentice Hall

Recursive relationships

“relationships among entities of a single class”

Page 53Figure 3-5 © 2000 Prentice Hall

E-R Diagram

Page 54Figure 3-6a © 2000 Prentice Hall

E-R Diagram

Page 54Figure 3-6b © 2000 Prentice Hall

Chapter 3

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Weak Entities

“an entity whose presence in the database depends (logically) on another entity”

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Subtype Entities“an entity that contains option sets

of attributes”

Page 56Figure 3-10b © 2000 Prentice Hall

E-R Diagram with all elements

Page 59Figure 3-11 © 2000 Prentice Hall

Chapter 3

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Drawing E-R diagrams

• IEW• IEF• DEFT• ER-WIN• Visio

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Jefferson Dance Club

Page 62Figure 3-14 © 2000 Prentice Hall

San Juan Charters

Page 66Figure 3-16 © 2000 Prentice Hall