- E. F. Codd:
Extending the Data Base Relational Model to Capture More Meaning (Abstract). SIGMOD Conference 1979: 161 - 1971
- E. F. Codd:
Further Normalization of the Data Base Relational Model. Research Report / RJ / IBM / San Jose, California RJ909 (1971) - 1970
- E. F. Codd:
A Relational Model of Data for Large Shared Data Banks. Commun. ACM 13(6): 377-387 (1970)