Olle, T. W., "An analysis of the flaws in the Schema DDL and proposed improvements" pp283-297

[IFIP] Proc. of IFIP TC-2 Special Working Conf., (1972) [IFIP] Proc. of IFIP TC-2 Special Working Conf., "An In-depth Technical Evaluation of the CODASYL DDL" 1972  

Languages mentioned DDL {1972} CODASYL Data Definition Language