As you design an object model for this problem, you consider the classes, the attributes, and the relations to declare as well as the constraints to define on them. The knowledge contained in the problem description (that is, the attributes, relations, and constraints) can be encapsulated in a few classes that you define here. Constraints are defined in class constructors so that they are automatically added for each new instance of the class.

You can use these different classes to model the problem:

After you define those classes, you will define accessors for their attributes so that the attributes can be used directly by constraints on set variables.