Layering as means for structuring Petri nets

In this paper we suggest to apply modelling with layers as an additional concept for structuring Petri system descriptions. After introducing the phenomena by an example the main task is to define how to get the whole Petri net description from the descriptions of aspects in subnets/subsystems (layers). The answer is given by defining the union of subnets and discussing the difficulties of defining the union of subsystems. Some remarks on how to apply these concepts are included