http://doi.acm.org/10.1145/800296.811515 db/conf/sigmod/ChamberlinB74.html Donald D. Chamberlin Raymond F. Boyce SEQUEL: A Structured English Query Language. 249-264 SIGFIDET74-1/P249.pdf 1974 conf/sigmod/74 SIGMOD Workshop, Vol. 1 db/conf/sigmod/sigmod74-1.html#ChamberlinB74