Normalisation: 1NF to BCNF

Codd's 1970 paper already asked for “normalized” relations with no repeating groups inside a field. In 1971 he went further and defined the second and third normal forms, a way to tell from the dependencies between attributes whether a table stores the same fact in more than one place.

In 1974 Raymond Boyce, co-author of SEQUEL, and Codd tightened the third form into a stricter one that now carries both their names: Boyce–Codd normal form. The rules sound abstract. The problems they prevent are very concrete: a lecturer's office stored on two hundred rows, and two hundred chances to get it wrong.