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Entity-Relationship (E-R) Model

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Title: Chapter 5 Entity-Relationship (E-R) Model Last modified by: Nancy Tsai Created Date: 2/14/1997 5:17:40 PM Document presentation format: On-screen Show – PowerPoint PPT presentation

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Title: Entity-Relationship (E-R) Model


1
Chapter 11 12
  • Entity-Relationship (E-R) Model

2
Agenda
  • Characteristics of E-R Model
  • Components of E-R Model
  • Example of E-R Model
  • Enhanced E-R Model

3
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
  • Unified Modeling Language (UML)

4
Components of E-R Model
  • Entity
  • Attribute
  • Key
  • Relationship
  • Structural constraints on relationship

5
Entity
  • Definition
  • An object or concept
  • Types
  • Strong entity (parent, owner, dominant)
  • Weak entity (child, dependent, or subordinate)
  • Diagram Notation
  • Rectangular

6
Attribute
  • Domain
  • Types
  • Single
  • Composite
  • Single-valued
  • Multi-valued
  • Derived

7
Key
  • Candidate key
  • Primary key
  • Composite key

8
Relationship
  • Definition
  • Association among entities
  • Diagram Notation
  • Line (relation or role name)
  • Degree of a relationship
  • Number of participating entities
  • Types
  • Unary (recursive relationship)
  • Binary
  • Ternary
  • Quaternary

9
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 (ambiguous pathway)
  • Chasm trap (missing pathway)

10
Enhanced Entity-Relationship Model
  • Additional entity types
  • Superclass including one or more distinct
    subgroups in the data model
  • Subclass a distinct subgroup of an entity type
    in the data model
  • Attribute Inheritance
  • Specialization hierarchy (specialization
    maximizing the differences between members of an
    entity by identifying their distinguishing
    characteristics)
  • Generalization hierarchy (generalization
    minimizing the differences between entities by
    identifying their common characteristics)
  • Is-A hierarchy
  • Constraints on specialization/generalization
  • Participation (mandatory, optional)
  • Disjoint disjoint (or), non-disjoint (and)
  • Other
  • Aggregation (has a or is part of)
  • Composition (strong ownership of aggregation)

11
Design Steps
  • Identify
  • Entity types, relationship types
  • Cardinality and participation constraints
  • Attributes
  • Keys
  • Specialize/generalize
  • EER diagram
  • EER model example

12
  • Create an enhanced ER diagram for a rental
    management using following entities
  • Rental agency
  • Staff
  • Part time
  • Full time
  • Owner
  • Renter
  • Property
  • Business
  • Home

13
Points To Remember
  • Characteristics of E-R Model
  • Components of E-R Model
  • Example of E-R Model
  • Enhanced E-R Model

14
Assignment
  • Review chapters 5, 6, 9, 10, 11, and 12
  • Read chapter 13
  • Homework assignment
  • 11.11 (enhanced e-r diagram)
  • Due date
  • Exam 2 date
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