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