What Is a Relational Database?

The concept of a relational database is not new. It was originally developed back in 1970 by Dr. E.F. Codd. He laid down the theory of relational databases in his seminal paper entitled A Relational Model of Data for Large Shared Data Banks published in Communications of the ACM (Association for Computing Machinery), Vol. 13, No. 6, June 1970.

The basic concepts of a relational database are fairly easy to understand. A relational database is a collection of related information that has been organized into structures known as tables . Each table contains rows that are further organized into columns . These tables are stored in the database in structures known as schemas , which are areas where database users may store their tables. Each user may also choose to grant permissions to other users to access their tables.

Most of us are familiar with data being stored in tables ”stock prices and train timetables are sometimes organized into tables. An example used in one of the schemas in this book is a table that records customer information for a hypothetical store. Part of this table consists of columns containing the customer s first name, last name , date of birth (dob), and phone number:

 first_name last_name dob phone ---------- ---------- ----------- ------------ John Brown 01-JAN-1965 800-555-1211 Cynthia Green 05-FEB-1968 800-555-1212 Steve White 16-MAR-1971 800-555-1213 Gail Black 800-555-1214 Doreen Blue 20-MAY-1970 

This table could be stored in a variety of forms: a piece of paper in a filing cabinet or ledger or in the file system of a computer, for example. An important point to note is that the information that makes up a database (in the form of tables) is different from the system used to access that information. The system used to access a database is known as a database management system .

In the case of a database consisting of pieces of paper, the database management system might be a set of alphabetically indexed cards in a filing cabinet. For a database accessed using a computer, the database management system is the software that manages the files stored in the file system of the computer. The Oracle database is one such piece of software; other examples include SQL Server, DB2, and MySQL.

Of course, every database must have some way to get data in and out of it, preferably using a common language understood by all databases. Today s database management systems implement a standard language known as Structured Query Language , or SQL. Among other things, SQL allows you to retrieve, add, update, and delete information in a database.