Exception handling in petri-net-based workflow management

Various classes of Petri nets have been established as conceptual models for modelling and control of workflows. Usually, these nets are enacted by administrators and there is no way to change the plan once enacted by the start of a computer-based interpretation of the net. In particular, necessary repetitions of wrong previous actions, changes of the business rules requiring changes of the process structure and changes of the organizational structure cannot be realized without restart of the whole net. In the context of a general definition of exceptions and using an example ("Planning permission processing" in Berlin) it is shown how an appropriate combination of the three (partly new) concepts of general task embedding, commitment and causality trees and of modular process nets has been used to implement a very flexible and adaptable workflow management concept.