Visual Basic 2005 for Programmers: Deitel Developer Series, Second Edition

20.2. Relational Databases

A relational database is a logical representation of data that allows the data to be accessed independently of its physical structure. A relational database organizes data in tables. Figure 20.1 illustrates a sample Employees table that might be used in a personnel system. The table stores the attributes of employees. Tables are composed of rows and columns in which values are stored. This table consists of six rows and five columns. The Number column of each row in this table is the table’s primary key—a column (or group of columns) in a table that requires a unique value that cannot be duplicated in other rows. This guarantees that a primary key value can be used to uniquely identify a row. A primary key that is composed ...