Tuple correlation calculus

Question

Is tuple safe correlation calculus an exhaustive language?

Answer 1

Forget about security. By Codd’s theorem , relational calculus is equivalent to first-order logic. FOL is very limited, it cannot express the fact that there is a route from point A to point B on some graph (it can express the fact that there is a route from point A to point B in a limited length, for example ∃ x ∃y ∃z ∃t route (a, x) and route (x, y) and route (y, z) and route (z, t) and route (t, b) mean a route of length 4).

See descriptive complexity for a description of what is the power of different logics.

Answer 2

According to Codd Theor , relational algebra and relational calculus are equivalent. It is well known that relational algebra is not Turing Complete, therefore, relational calculus is not.

[Change] You cannot, for example, perform aggregate operations (eg, sum, max) or make recursive queries in relational algebra / calculus. See here (near the end).