Dr. Edgar Frank Codd (August 19, 1923 – April 18, 2003) was a computer scientist at IBM and developed the relational model for database management ( theoretical basis for relational databases). Codd proposed 13 rules (numbered zero to twelve) and asserted that if a Database Management System meets these rules, it can be called as a Relational Database Management System. These rules are called as Codd's12 rules. Very few commercial product follows all.