Mathematical modelling is often associated with terms such as intuition. However, an experienced modeller will usually have a clear procedure to deduce a model. In a first step he or she will analyse experimental data on a qualitative level. Only those models are then tested in a quantitative identification which passed the qualitative check. This efficient procedure is translated here into methods which can be coded in a computer program. A tool TAM-C is introduced which automatically finds structures and parameters of formal kinetics of chemical reaction systems. The main part of the contribution is dedicated to the qualitative preselection of possible model candidates.