Marco A. Casanova , Paulo A. S. Veloso , Antonio L. Furtado, "Formal data base specification: an eclectic perspective"

[ACM SIGACT-SIGMOD] (1984) [ACM SIGACT-SIGMOD] Proceedings of the 3rd ACM SIGACT-SIGMOD symposium on Principles of database systems, April 02-04, 1984, Waterloo, Ontario, Canada  

Languages mentioned DDL {1980} Data definition language DML {1980}