Codd's twelve rules are a set of thirteen rules (numbered zero to twelve) 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 (RDBMS). They are sometimes referred to as "Codd's Twelve Commandments".

History

Codd originally set out the rules in 1970, and developed them further in a 1974 conference paper. His aim was 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. While in 1999, a textbook stated "Nowadays, most RDBMSs ... pass the test", another in 2007 suggested "no database system complies with all twelve rules." Codd himself, in his book "The Relational Model for Database Management: Version 2", acknowledged that while his original set of 12 rules can be used for coarse distinctions, the 333 features of his Relational Model Version 2 (RM/V2) are needed for distinctions of a finer grain.

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: Relational Operations Rule / 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: