Overview of the Relational Model

The relational model was formally introduced by Dr. E. F. Codd in 1970 and has evolved since then, through a series of writings. The model provides a simple, yet rigorously defined, concept of how users perceive data. The relational model represents data in the form of two-dimension tables. Each table represents some real-world person, place, thing, or event about which information is collected. A relational database is a collection of two-dimensional tables. The organization of data into relational tables is known as the logical view of the database. That is, the form in which a relational database presents data to the user and the programmer. The way the database software physically stores the data on a computer disk system is called the internal view. The internal view differs from product to product and does not concern us here.

A basic understanding of the relational model is necessary to effectively use relational database software such as Oracle, Microsoft SQL Server, or even personal database systems such as Access or Fox, which are based on the relational model.

This document is an informal introduction to relational concepts, especially as they relate to relational database design issues. It is not a complete description of relational theory.

This section discusses the basic concepts—data structures, relationships, and data integrity—that are the basis of the relational model.

• Data Structure and Terminology
• Notation
• Properties of Relational Tables
• Relationships and Keys
• Data Integrity
• Relational Data Manipulation
• Normalization
• Advanced Normalization