A computer determines that the type of one or more of a relational operator and operands of a relational expression originated in a first type system, and determines the sign of at least one of the operands. The computer rewrites the relational expression based on the sign of at least one of the operands, sends the rewritten relational expression for evaluation in a second type system, and receives the evaluated rewritten relational expression after evaluation in the second type system. The computer can rewrite the relational expression by generating a group of terms joined disjunctively, as well as by generating a group of conjunctive terms joined disjunctively.