Z and high level Petri nets

High level Petri nets have tokens with values, traditionally called colors, and transitions that produce tokens in a functional way, using the consumed tokens as arguments of the function application. Large nets should be designed in a topdown approach and therefore we introduce a hierarchical net model which combines a data flow diagram technique with a high level Petri net model. We use Z to specify this net model, which is in fact the metamodel for specific systems. Specific models we specify partly by diagrams and partly in Z. We give some advantages and disadvantages of using Z in this way. Finally we show how to specify systems by means of an example