Kees M. van Hee

The Petri net markup language: concepts, technology, and tools

The Petri Net Markup Language (PNML) is an XML-based interchange format for Petri nets. In order to support different versions of Petri nets and, in particular, future versions of Petri nets, PNML allows the definition of Petri net types. Due to this flexibility, PNML is a starting point for a standard interchange format for Petri nets. This paper discusses the design principles, the basic concepts, and the underlying XML technology of PNML. The main purpose of this paper is to disseminate the ideas of PNML and to stimulate discussion on and contributions to a standard Petri net interchange format.

Global Convergence of Genetic Algorithms: A Markov Chain Analysis

In this paper we are trying to make a step towards a concise theory of genetic algorithms (GAs) and simulated annealing (SA). First, we set up an abstract stochastic algorithm for treating combinatorial optimization problems. This algorithm generalizes and unifies genetic algorithms and simulated annealing, such that any GA or SA algorithm at hand is an instance of our abstract algorithm. Secondly, we define the evolution belonging to the abstract algorithm as a Markov chain and find conditions implying that the evolution finds an optimum with probability 1. The results obtained can be applied when designing the components of a genetic algorithm.

Soundness and separability of workflow nets in the stepwise refinement approach

Workflow nets are recognized as a modelling paradigm for the business process modelling. We introduce and investigate several correctness notions for workflow nets, ranging from proper termination of cases to their mutual independence. We define refinement operators for nets and investigate preservation of correctness through these operators. This gives rise to a class of nets that are provably correct.

Conceptual model for online auditing

The independent verification of the right applications of business rules in an information system is a task for auditors. The increasing complexity of information systems, and the high risks associated with violations of business rules, have created the need for Online Auditing Tools. In this paper we sketch a conceptual design for such a tool. The components of the tool are described briefly. The focus is on the database and the conformance checker, which are described in detail. The approach is illustrated with an example and some preliminary case studies from industry.

Generalised soundness of workflow nets is decidable

We investigate the decidability of the problem of generalised soundness for Workflow nets: ”Every marking reachable from an initial marking with k tokens on the initial place terminates properly, i.e. it can reach a marking with k tokens on the final place, for an arbitrary natural number k”. We start with considering simple correctness criteria for Workflow nets and reduce them to the check of structural properties formulated in terms of traps and siphons, which can be easily checked. We call the nets that possess those properties Batch Workflow nets (BWF-nets). We show that every sound WF-net can be transformed to a BWF-net with the same behaviour. Then we use algebraic methods to prove that generalized soundness is decidable for BWF-nets and give a decision procedure.

Nested nets for adaptive systems

We consider nested nets, i.e. Petri nets in which tokens can be Petri nets themselves. We study the value semantics of nested nets rather than the reference semantics, and apply nested nets to model adaptive workflow, i.e. flexible workflow that can be modified during the execution. A typical domain with a great need for this kind of workflow is health care, from which domain we choose the running example. To achieve the desired flexibility we allow transitions that create new nets out of the existing ones. Therefore, nets with completely new structure can be created at the run time. We show that by careful selection of basic operations on the nets we can obtain a powerful modeling formalism that enforces correctness of models. Moreover, the formalism can be implemented based on existing workflow engines.

Using Formal Analysis Techniques in Business Process Redesign

Formal analysis techniques can deliver important support during business process redesign efforts. This chapter points out the (potential) contribution of these formal analysis techniques by giving an outline on the subject first. Next, a specific, newly developed formal technique is discussed.

Soundness of resource-constrained workflow nets

We study concurrent processes modelled as workflow Petri nets extended with resource constraints. We define a behavioural correctness criterion called soundness: given a sufficient initial number of resources, all cases in the net are guaranteed to terminate successfully, no matter which schedule is used. We give a necessary and sufficient condition for soundness and an algorithm that checks it.

Consistency in model integration

State-of-the-art systems engineering uses many models reflecting various aspects of the modeled system. A major task of system engineers is to ensure consistency between the many models. We present an approach to the engineering of complex systems based on the modeling of use cases and object life cycles as Petri nets. Synchronization by place fusion allows the derivation of an integrated model that can be verified and validated. We illustrate our approach by a case study.

Colored petri nets to verify extended event-driven process chains

Business processes are becoming more and more complex and at the same time their correctness is becoming a critical issue: The costs of errors in business information systems are growing due to the growing scale of their application and the growing degree of automation. In this paper we consider Extended Event-driven Process Chains (eEPCs), a language which is widely used for modeling business processes, documenting industrial reference models and designing workflows. We describe how to translate eEPCs into timed colored Petri nets in order to verify processes given by eEPCs with the CPN Tools.