Your choice of types for variables will also be important in your model. The right kind of variables can be coded directly from properties of the model. Think, for example, in terms of constrained set variables. According to the types of variables that you choose, you'll be able to express constraints more or less easily.

Use symbolic constraints as much as possible; by symbolic constraints, we mean such constraints as whether a variable is an element of a set, or what the cardinality of a set may be.

Symbolic constraints often enable you to reduce the number of variables in the program. Such a reduction in variables will be useful since the apparent search space is exponential in terms of the number of variables, but it is only polynomial with respect to the size of their domains.