Babad, Yair M. and Hoffer, Jeffrey A. "Even no data has a value" p748-756
(1984)
[ACM] (1984)
[ACM] CACM 27(08) (August 1984)
Languages mentioned
FOCUS
{1979} Hierarchical database language
SYSTEM 2000
{1973}
TABOL
{1967} Table-oriented language