DPL ALPHA System and Codd's Cellular Space
G. Fay · Journal of Cybernetics · 1974
DPL ALPHA differs from Codd's original DSL ALPHA only in one essential aspect, namely, that in Data Processing Language ALPHA primitive notions are mostly from predicate calculus (i.e., relation calculus without quantifiers). Boolean algebra and edge-notched card system rather than from relation calculus and relational algebra. ALPHA concepts then can be synthetized from these. [6]