Edgar F. Codd invented the relational database. In his article "A Relational Model of Data for Large Shared Data Banks," which first appeared in Communications of the ACM, Vol. 13, No. 6, June 1970, Codd describes the 12 characteristics of a relational database system. Search the Intelligent Enterprise site (www.intelligententerprise.com) for commentary and discussion on the original 1970 article as well as on other articles by Codd. For additional insight into relational databases, refer to Codd's classic reference book, The Relational Model for Database Management (Addison-Wesley, 1990) in which he expands on his earlier work and defines 333 characteristics of a "pure" relational database system.

In "Overview of the Relational Model" at www.utexas.edu/cc/dbms/utinfo/relmod/index.html from the University of Texas at Austin's Database Management Services, you can find a simple explanation of the relational model and reasons why you might need to understand it. The Web-based document discusses the relational data structure, including notation, properties of relational tables, relational keys, and data integrity; manipulation of relational data; and normalization. There are also a brief reading list and links to other database resources on the Internet.

C. J. Date is one of the most prolific writers on the topic of databases. Through his extensive teaching, training, and writing activities, Date has explained the relational model to thousands of software engineers, software designers, educators, students, journalists, and end users. In a 1994 interview, Date talked about the future of the database industry and integrating object-oriented database concepts with relational concepts. Date's classic book on databases is now in its sixth edition: An Introduction to Database Systems (Addison-Wesley, 1999).