Optimization problems appear in many applications. Many companies around the world are very interested in solving such problems to decrease their cost and increase their benefit. One of the difficulties in solving optimization problems is to find a proper formulation of the problem. Modelling languages provide high-level structures and constraints to help modellers to find a conceptual model of the problem. In this paper, we explain how modelling languages try to make the task of modelling easy while ensure that conceptual models remain executable.