Datasheet

SQL and Relational
Database Management
Systems
IN THIS CHAPTER
Understanding databases
Characteristics of a good
database
The database market
Real-life database examples
Brief database history
SQL standards and
implementation differences
I
nformation may be the most valuable commodity in the modern world.
It can take many different forms — such as accounting and payroll
information, information about customers and orders, scientific and
statistical data, graphics, or multimedia. We are virtually swamped with
data, and we cannot — or at least we’d like to think about it this way —
afford to lose it. These days we simply have too much data to keep storing
it in file cabinets or cardboard boxes. The need to store large collections
of persistent data safely, ‘‘slice and dice’’ it efficiently from different angles
by multiple users, and update it easily when necessary is critical for every
enterprise. That need mandates the existence of databases, which accom-
plish all the tasks listed, and then some. To put it simply, a database is just
an organized collection of information — with emphasis on ‘‘organized.’’
A more specific definition often used as a synonym for ‘‘database’’ is database
management system (DBMS). That term is wider and, in addition to the stored
information, includes some methods to work with data and tools to maintain it.
DBMS can be defined as a collection of interrelated
data plus a set of programs to access, modify, and
maintain the data. More about DBMS later in this chapter.
Desirable Database
Characteristics
There are many differing ideas about what a database is and what it should
do. Nevertheless, all modern databases should have at least the following
characteristics.
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