relational calculus
<database> An operational methodolgy, founded on {predicate
calculus}, dealing with descripitive expressions that are
equivalent to the operations of {relational algebra}. {Codd's
reduction algorithm} can convert from {relational calculus} to
{relational algebra}.
Two forms of the relational calculus exist: the {tuple
calculus} and the {domain calculus}.
["An Introduction To Database Systems" (6th ed), C. J. Date,
Addison Wesley].
(1998-10-05)