OCL2FOL+: Coping with Undefinedness

Abstract. At present, the OCL language includes two constants, null and invalid, to represent undefinedness. This effectively turns OCL into a four-valued logic. It makes also problematic its mapping to first-order logic and, as a consequence, hinders the use of first-order automated-reasoning tools for OCL reasoning. We address this problem and propose a solution, grounded on the same principles underlying OCL2FOL, in order to cope with undefinedness in OCL.