Fundamentals of Database Management Systems, Second Edition

CHAPTER 6

THE RELATIONAL DATABASE MODEL: ADDITIONAL CONCEPTS

Chapter 5 defined the basic terminology of relational database and then demonstrated some fundamental ideas about constructing relations in relational databases and manipulating data in them. The discussion focused on relationships between two different entity types, i.e. binary relationships. This chapter will go beyond binary relationships into unary and ternary relationships. It will then address the important issue of referential integrity.

OBJECTIVES

• Describe how unary and ternary relationships are implemented in a relational database.
• Explain the concept of referential integrity.
• Describe how the referential integrity restrict, cascade, and set-to-null delete rules operate in a relational database.

CHAPTER OUTLINE

• Introduction
• Relational Structures for Unary and Ternary Relationships
  • Unary One-to-Many Relationships
  • Unary Many-to-Many Relationships
  • Ternary Relationships
• Referential Integrity
  • The Referential Integrity Concept
  • Three Delete Rules
• Summary

INTRODUCTION

The previous chapter talked about how binary relationships, i.e. those involving two entity types, can be constructed in relational databases so that the data can be integrated while data redundancy is avoided. Unary relationships, with one entity type, and ternary relationships, with three entity types, while perhaps not quite as common as binary relationships, are also facts of life in the real world and so must also be handled properly in relational ...