Codd's twelve rules[1] 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).
[4] Codd originally set out the rules in 1970, and developed them further in a 1974 conference paper.
[5] 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.
[citation needed] While in 1999, a textbook stated "Nowadays, most RDBMSs ... pass the test",[5] another in 2007 suggested "no database system complies with all twelve rules.
"[6] 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.