Transcript Chapter 3: The Entity

Database Processing
Chapter 3
The Entity-Relationship Model
David M. Kroenke
© 2000 Prentice Hall
Chapter 3
Data Modeling
• Process of creating a logical
representation of the structure of
the database
• The most important task in database
development
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Chapter 3
Entity-Relationship Model
• E-R Model
• Peter Chen, 1976
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Entities
“something that users track”
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Figure 3-1
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Chapter 3
Attributes (properties)
“describe the entity’s characteristics”
Entity: Employee
Attributes: EmployeeName, Extension,
DateOfHire, JobSkillCode
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Chapter 3
Identifier
“attributes that name entity instances”
Entity: Employee
Identifier: SocialSecurityNumber
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Relationships
“associations between entities”
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Figure 3-3
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Cardinality
“maximum or minimum number of
entities that can occur on one side of
a relationship”
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Figure 3-4
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Recursive relationships
“relationships among entities of a single
class”
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Figure 3-5
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E-R Diagram
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Figure 3-6a
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E-R Diagram
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Figure 3-6b
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Chapter 3
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”
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Figure 3-10b
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E-R Diagram with all elements
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Figure 3-11
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Chapter 3
Drawing E-R diagrams
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IEW
IEF
DEFT
ER-WIN
Visio
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Jefferson Dance Club
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Figure 3-14
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San Juan Charters
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Figure 3-16
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