Relational Calculus
Comes in two flavors: Tuple relational calculus (TRC) and Domain relational calculus (DRC).
Calculus has variables, constants, comparison ops, logical connectives, and quantifiers.
- TRC: Variables range over (i.e., get bound to) tuples.
- DRC: Variables range over domain elements (= field values).
- Both TRC and DRC are simple subsets of first-order logic.
Expressions in the calculus are called formulas. An answer tuple is essentially an assignment of constants to variables that make the formula evaluate to true.