Analysis by contract: An introduction to UML's object constraint language (OCL)

The roots of object oriented development are in simulation. These roots have something to tell rls about how to use object-oriented development methods. The exploratory steps ill any development, taken for example to understand a problem domain, call be supported by building informal simulations of the domain. The movement inherent in a simulation provides a useful complement to the static nature of many conventional models. More formal models can be built so that they are capable of supporting simulation, to ensure that they accurately model a problem domain. In other words, the formal models exhibit continuity with the part of the world they model. A small example shows the dangers of losing this property of continuity.