Computer Programming Concepts and Visual Basic David I. Schneider

11.1 AN INTRODUCTION TO DATABASES
The management of databases is the number one use of computers today. Airlines use databases
to handle nearly 1.5 billion passenger reservations per year. The 6500 hospitals in the United
States use databases to document the care of over 30 million patients per year. Banks in the
United States use databases to monitor the use of 350 million credit cards. Although databases
vary considerably in size and complexity, most of them adhere to the fundamental principles
of design discussed in this chapter. That is, they are composed of a collection of interrelated
tables.
A table is a rectangular array of data. Table 11.1 provides information about large cities.
Each column of the table, called a field, contains the same type of information. (The third
column gives the 1995 population in millions and the fourth column gives the projected 2015
population in millions.) The names of the fields are city, country, pop1995, and pop2015.
Each row, called a record, contains the same type of information as every other row. Also,
the pieces of information in each row are related; they all apply to a specific city. Table 11.2,
Countries, has three fields and nine records.
TABLE 11.1
Cities
city country pop1995 pop2015
Beijing China 12.4 19.4
Bombay India 15.1 27.4
Calcutta India 11.7 17.6
Los Angeles USA 12.4 14.3
Mexico City Mexico 15.6 18.8
New York USA 16.3 17.6
Sao Paulo Brazil 16.4 20.8
Shanghai China 15.1 23.4
Tianjin China 10.7 17.0
Tokyo Japan 26.8 28.7
323