Reviewing the model-based approach to scientific problem solving from a very general point of view, we observe the following pattern of actions (Figure 3.1.1): Starting with the real world situation, we recognize a problem we want to eliminate or improve. To tackle this problem using scientific methods we first build a model,and try to find a solution of the problem in the world of the model. The obtained solution in the model world has to be interpreted in the real world and finally we have to implement the solution in the real world to eliminate the problem.