Featherweight OCL
Achim D. Brucker, Burkhart Wolff · 2012
At its origins, OCL was conceived as a strict semantics for undefinedness, with the exception of the logical connectives of type Boolean that constitute a three-valued propositional logic. Recent versions of the OCL standard added a second exception element, which, similar to the null references in programming languages, is given a non-strict semantics.