Chapter 2 Data Modeling Fundamentals of Database Management
Chapter 2 Data Modeling Fundamentals of Database Management Systems, 2 nd ed by Mark L. Gillenson, Ph. D. University of Memphis John Wiley & Sons, Inc.
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-tomany unary, binary, and ternary relationships. 2 -2
Chapter Objectives ¨ Recognize and describe intersection data. ¨ Model data in business environments by drawing entity-relationship diagrams that involve unary, binary, and ternary relationships. 2 -3
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 2 -4
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. 2 -5
E-R Model Entity (and its attributes) ¨ Rectangular shape ¨ Salesperson = a type of entity ¨ Name of entity is in caps above the separator line. 2 -6
E-R Model Entity (and its attributes) ¨ Entity type’s attributes are shown below the separator line. ¨ PK and boldface denote the attribute(s) that constitute the entity type’s unique identifier. 2 -7
Relationships ¨ Associations between entities ¨ Different kinds: ª Binary relationships ª Unary relationships ª Ternary relationships 2 -8
Binary Relationships Simplest kind of relationship ¨ Relationship between two entity types ¨ A salesperson “sells” products or products are “sold” by salespersons ¨ 2 -9
Cardinality ¨ Represents the maximum number of entities that can be involved in a particular relationship. ª One-to-One Binary Relationship ª One-to-Many Binary Relationship ª Many-to-Many Binary Relationship 2 -10
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. 2 -11
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. 2 -12
Many-to-Many Binary Relationship ¨ M-M ¨ “many” can be either an exact number or have a known maximum. 2 -13
Cardinality 2 -14
Modality ¨ The minimum number of entity occurrences that can be involved in a relationship. ¨ “inner” symbol on E-R diagram (“outer” symbol is cardinality) 2 -15
Cardinality & Modality 2 -16
Intersection Data ¨ Describes the relationship between two entities. ¨ Used with many-to-many relationships. ¨ Represented on E-R diagram as an “associative entity” 2 -17
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. 2 -18
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. 2 -19
Associative Entity ¨ 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. 2 -20
Unary Relationships ¨ Associate occurrences of an entity type with other occurrences of the same entity type. ¨ Cardinality: ª One-to-One Unary Relationship ª One-to-Many Unary Relationship ª Many-to-Many Unary Relationship 2 -21
¨ Unary Relationships 2 -22
Ternary Relationship ¨ Involves three different entity types. 2 -23
¨ The General Hardware Company E-R Diagram ¨ Customer Employee is a dependent entity. 2 -24
Good Reading Bookstores 2 -25
World Music Association 2 -26
Lucky Rent-A-Car 2 -27
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