THE RELATIONAL DATABASE MODEL: INTRODUCTION - Fundamentals of Database Management Systems - page 106

The Relational Select Operator
The Relational Project Operator
Combination of the Relational
Select and Project Operators
Extracting Data Across Multiple
Relations: Data Integration

Example: Good Reading Book Stores
Example: World Music Association
Example: Lucky Rent-A-Car
Summary

INTRODUCTION

Several factors converged in the early 1980s to begin turning the tide toward
relational database. One was that the performance issues that held back its adoption
in the 1970s began to be resolved. Another was that, after a decade of use
of hierarchical and network database management systems, information systems
professionals were interested in an alternative that would move toward simplifying
the database design process and produce database structures that were easier to use
and understand at all levels. Also, at this time there was increasing interest in a
DBMS environment that would allow easier, more intuitive access to the data by an
increasingly broad range of personnel. Finally, the early 1980s saw the advent of
the personal computer . As software developers began trying to create all manner
of applications and supporting software utilities for the PC, it quickly became clear
that the existing hierarchical and network database approaches would not work in
the PC environment, for two reasons. One was that these DBMSs were simply too
large to store and use on the early PCs. The other was that they were too complex to
be used by the very broad array of non-information-systems professionals at whom
the PCs were targeted.
Today, the relational approach to database management is by far the primary
database management approach used in all levels of information systems and for
most application purposes, from accounting to banking to manufacturing to sales on
the World Wide Web. Relational database management is represented today by such
products as Microsoft Access and SQL Server, Oracle, Sybase, and IBM's DB2 and
Informix. While these and other relational database systems differ in their features
and implementations, they all share a common data structure philosophy and a
common data access tool: Structured Query Language (SQL) (often pronounced
''sequel''). This chapter will focus on the basic concepts of how data is stored
and retrieved in a relational database by a relational DBMS. Chapter 6 will discuss
some additional relational database concepts. Then, Chapter 7 will describe logical
database design and Chapter 8 will go into physical database design.

THE RELATIONAL DATABASE CONCEPT

Relational Terminology
In spite of the apparent conflict between non-redundant, linear file data storage
and data integration demonstrated in Chapter 3, the relative simplicity of simple,
linear files or structures that resemble them in a true database environment is very
desirable. After all, the linear file arrangement is the most basic and commonly used
data structure there is. This is precisely one of the advantages of relational database
management.