Modelling with Option Types in MiniZinc

Abstract

Option types are a powerful abstraction that allows the concise modelling of combinatorial problems where some decisions are relevant only if other decisions are made. They have a wide variety of uses: for example in modelling optional tasks in scheduling, or exceptions to a usual rule. Option types represent objects which may or may not exist in the constraint problem being modelled, and can take an ordinary value or a special value ⊤ indicating they are absent. The key property of variables of option types is that if they take the value ⊤ then the constraints they appear in should act as if the variable was not in the original definition. In this paper, we explore the different ways that b..