Codd's 12 rules


Codd's twelve rules are a set of thirteen rules proposed by Edgar F. Codd, a pioneer of the relational model for databases, designed to define what is required from a database management system in order for it to be considered relational, i.e., a relational database management system. They are sometimes jokingly referred to as "Codd's Twelve Commandments".

Details

Codd produced these rules as part of a personal campaign to prevent the vision of the original relational database from being diluted, as database vendors scrambled in the early 1980s to repackage existing products with a relational veneer. Rule 12 was particularly designed to counter such a positioning.

Rules

Rule 0: The foundation rule:
Rule 1: The information rule:
Rule 2: The guaranteed access rule:
Rule 3: Systematic treatment of null values:
Rule 4: Dynamic online catalog based on the relational model:
Rule 5: The comprehensive data sublanguage rule:
Rule 6: The view updating rule:
Rule 7: Possible for high-level insert, update, and delete:
Rule 8: Physical data independence:
Rule 9: Logical data independence:
Rule 10: Integrity independence:
Rule 11: Distribution independence:
Rule 12: The nonsubversion rule: