Entity Relationship Modeling

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CHAPTER

three

Entity-Relationship
Modeling
chapterE W
OVERVI

3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
3.10
3.11
3.12
3.13
3.14
3.15
3.16
3.17
3.18
3.19
3.20
3.21
3.22

Introduction
The Entity-Relationship Model
Entity
Attributes
Relationships
Degree of a Relationship
Cardinality of a Relationship
Unary Relationship
Binary Relationship
Ternary Relationships
Attributes of Relationships
Associative Entities
Weak Entity Types
Enhanced Entity-Relationship Modeling
Superclass, Subclass, and Relationships
Generalization and Specialization Process
Participation and Disjoint Constraints
Superclass/Subclass Hierarchy
Case Study: Conceptual Design for University Database
In-Class Assignment
Summary
Exercises

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CHAPTER 3

3.1

■

Entity-Relationship Modeling

Introduction
In Chapter 2, we introduced data models. A data model is an integrated collection of concepts that represents real world objects, events, and their relationships. We also briefly discussed two types of data models: object-based data models and relation-based data models. It is a common practice in database design to develop an object-based model first and then to systematically convert the model into a relation-based model, which is more suitable for database implementation. In this chapter, we will focus on conceptual database design using object-based models.
In Chapter 4, we will discuss the relational data models.
The three most popular object-based models discussed in database literature are the entityrelationship model, the functional model, and the object-oriented model. The entity-relationship model has emerged as one of the most popular techniques in the design of databases due to its inherent advantages. The entity-relationship