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Chapter 3 Data Modeling. Fundamentals of Database Management Systems by Mark L. Gillenson, Ph.D. University of Memphis Presentation by: Amita Goyal Chin, Ph.D. Virginia Commonwealth University John Wiley & Sons, Inc. Chapter Objectives.

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chapter 3 data modeling

Chapter 3Data Modeling

Fundamentals of Database Management Systems


Mark L. Gillenson, Ph.D.

University of Memphis

Presentation by: Amita Goyal Chin, Ph.D.

Virginia Commonwealth University

John Wiley & Sons, Inc.

chapter objectives
Chapter Objectives
  • Explain the concept and practical use of data modeling.
  • Recognize which relationships in the business environment are unary, binary, and ternary relationships.
  • Describe one-to-one, one-to-many, and many-to-many unary, binary, and ternary relationships.
chapter objectives3
Chapter Objectives
  • Recognize and describe intersection data.
  • Model data in business environments by drawing entity-relationship diagrams that involve unary, binary, and ternary relationships.
essence of data modeling
Essence of Data Modeling
  • Exploring the different ways that entities can relate to each other as they always do in the real world
  • Devising a way of recording, of diagramming, the entities and the ways in which they interrelate in the business environment
entity relationship e r model
Entity-Relationship (E-R) Model
  • A diagramming technique
  • Diagrams entities (with attributes) and the relationship between the entities.
  • There are many variations of E-R diagrams in use.
e r model entity and its attributes
E-R Model Entity (and its attributes)
  • Rectangular shape
  • Salesperson = a type of entity
  • Name of entity is in caps above the separator line.
e r model entity and its attributes7
E-R Model Entity (and its attributes)
  • Entity type’s attributes are shown below the separator line.
  • An asterisk denotes attribute(s) that constitute the entity type’s unique identifier.
  • Associations between entities
  • Different kinds:
    • Binary relationships
    • Unary relationships
    • Ternary relationships
binary relationships
Binary Relationships
  • Simplest kind of relationship
  • Relationship between two entity types
  • Diamond-shaped box represents relationship
  • A salesperson “sells” products or products are sold by salespersons
  • Represents the maximum number of entities that can be involved in a particular relationship.
    • One-to-One Binary Relationship
    • One-to-Many Binary Relationship
    • Many-to-Many Binary Relationship
one to one binary relationship
One-to-One Binary Relationship
  • 1-1
  • A single occurrence of one entity type can be associated with a single occurrence of the other entity type and vice versa.
one to many binary relationship
One-to-Many Binary Relationship
  • 1-M
  • Use “crow’s foot” to represent the multiple association.
  • “many” = the maximum number of occurrences that can be involved, means a number that can be 1, 2, 3, ... n.
many to many binary relationship
Many-to-Many Binary Relationship
  • M-M
  • “many” can be either an exact number or have a known maximum.
  • The minimum number of entity occurrences that can be involved in a relationship.
  • “inner” symbol on E-R diagram (“outer” symbol is cardinality)
intersection data
Intersection Data
  • Describes the relationship between two entities.
  • Used with many-to-many relationships.
  • Represented on E-R diagram in a special five-sided intersection data box, which is attached to the relationship diamond between the two entity boxes.
many to many binary relationship with intersection data
Many-to-Many Binary Relationship with Intersection Data
  • For example, we know not only that salesperson 137 sold some of product 24013 but also how many units of that product that salesperson sold.
associative entity
Associative Entity
  • Entities can have attributes; many-to-many relationships can have attributes.
  • Many-to-many relationship may be treated similarly to entities in an E-R diagram.
associative entity20
Associative Entity
  • Should you diagram as associative entity or many-to-many relationship?
    • personal taste
    • follow company standards
  • The unique identifier of the associative entity is usually the combination of the unique identifiers of the two entities in the many-to-many relationship.
unary relationships
Unary Relationships
  • Associate occurrences of an entity type with other occurrences of the same entity type.
  • Cardinality:
    • One-to-One Unary Relationship
    • One-to-Many Unary Relationship
    • Many-to-Many Unary Relationship
ternary relationship
Ternary Relationship
  • Involves three different entity types.
Ternary Relationship: The General Hardware Company E-R Diagram
  • Customer Employee, a dependent entity, is distinguished by a diagonal hash mark in each corner of its attribute area.

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