1. A relational model of data for large shared data banks;Codd;Commun. ACM,1970
2. Data And Reality;Kent,1978
3. A gross architecture for the next generation data base management systems;Nijssen,1976
4. SEQUEL: A structured English query language;Chamberlin,1974
5. A data base sublanguage founded on the relational calculus;Codd,1971