Chapter 11

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Chapter 11 12Entity-Relationship (E-R) Model

• Characteristics of E-R Model
• Components of E-R Model
• Example of E-R Model
• Enhanced E-R Model

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Characteristics of E-R Model

• Semantic data model
• Express the logical properties of an enterprise
  database
• Design tools and documentation for data base
  structure
• No physical DBMS
• Proposed by Dr. Peter Chen

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Components of E-R Model

• Entity
• Attribute
• Key
• Relationship
• Structural constraints on relationship

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Entity

• Definition
• An object or concept
• Types
• Strong entity (parent, owner, dominant)
• Weak entity (child, dependent, or subordinate)
• Diagram Notation
• Rectangular

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Attribute

• Domain
• Types
• Single
• Composite
• Single-valued
• Multi-valued
• Derived

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Key

• Candidate key
• Primary key
• Composite key
• Alternative key

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Relationship

• Definition
• Association among entities
• Diagram Notation
• Line (role name)
• Degree of a relationship
• number of participating entities
• types
• Unary (recursive relationship)
• Binary
• Ternary
• Quaternary

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Structural Constraints on Relationship

• Cardinality constraints
• Zero-to-one 0..1
• Zero-to-many 0..
• One-to-many 1..
• Many-to-many ..
• Participation constraints
• Total (mandatory, every one involved)
• Partial (optional, only some involved)
• Improper relationship
• Fan trap
• Chasm trap

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Enhanced Entity-Relationship Model

• Additional entity types
• Superclass (generalization)
• Subclass (specialization)
• Constraints
• Participation (mandatory, optional)
• Disjoint disjoint (or), non-disjoint (and)
• Attribute Inheritance
• Specialization hierarchy
• Generalization hierarchy
• Other
• Aggregation (has a or is part of)
• Composition (strong ownership of aggregation)

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Design Steps

• Identify
• Entity types, relationship types
• Cardinality and participation constraints
• Attributes
• Keys
• Specialize/generalize
• EER diagram
• EER model example

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Assignment

• Review chapters 9-12
• Read chapter 13
• Homework assignment
• 11.11 (enhanced e-r diagram)
• Due date