Introduction to the Relational Model
The relational model was conceived in the 1960s by Edgar F. Codd, who worked for IBM. It is a simple yet rigorously defined conceptualization of how users perceive and work with data. It addresses the three major aspects of data processing in the following way, according to An Introduction to Database Systems, 8th edition by C. J. Date (Addison-Wesley, 2003):
Structural The data is perceived by the user as tables and nothing but tables.
Manipulative Users manipulate the data with an open-ended set of relational operators. The operators constitute the relational algebra.
Integrity The tables must satisfy defined integrity constraints.
The structural aspect can also be expressed by the Information Principle, which ...