This volume contains 13 selected papers from the 28th International Conference on Applications and Theory of Petri Nets and Other Models of Concurrency, which was held in Siedlce, Poland, in June 2007. They cover a wide range of topics, and vary considerably in depth and scope.

The first three papers deal with teaching concurrency. They are: “Constructive Alignment for Teaching Model-Based Design for Concurrency,” by C. Braband; “Teaching Modeling and Validation of Concurrent Systems Using Colored Petri Nets,” by L.M. Kristensen and K. Jensen; and “Teaching Concurrency Concepts to Freshmen,” by C. Eisentraut and H. Hermanns. Of these, the second is informative and the third is rather interesting.

The next paper, “TAPAs: A Tool for the Analysis of Process Algebra,” by G. Calzolai et al., introduces a freeware language designed to use process algebras to specify and analyze concurrent systems. This language is designed as a teaching aid, not to generate high-performance solutions.

The next two papers deal with process mining: “Translating Message Sequence Charts to Other Process Languages Using Process Mining,” by K.B. Lassen and B.F. van Dongen, and “Net Components for the Integration of Process Mining into Agent-Oriented Software Engineering,” by L. Cabac and N. Denz. The first emphasizes the use of message sequence charts, rather than event logs of information systems. The second considers the use of process mining to understand software engineering.

In the paper “Time Recursive Petri Nets,” D. Dahmani et al. propose an extension of recursive Petri nets to include the semantics of time Petri nets. They give a formal definition, as well as some properties of such nets, but the motivation for why one would actually need this new structure is weak. Another variant of Petri nets is a case-handling system, introduced in “Designing Case Handling Systems,” by K.M. van Hee et al. Such systems combine Petri nets and relational data models.

In “Model-Driven Testing Based on Test History,” I.C. Ramos et al. present a software testing method consisting of automatic generation of efficient test procedures, using models of the system. The system given here runs as one sequential process, but the authors note that it is only a stepping stone to a more realistic model, with several parallel threads. The approach is promising and I hope that future work will be published along these lines.

The paper “Assessing State Spaces Using Petri-Net Synthesis and Attribute-Based Visualization,” by H.M.W. Verbeek et al., is based on the use of the Petrify system for transforming finite transition systems into Petri nets. Unfortunately, the Web address given for this software is no longer valid, which illustrates the problem of including URLs in printed material--they are often obsolete by the time the book is published.

One of the classical problems of Petri nets is assessing reachability. This problem is confronted in “Directed Unfolding of Petri Nets,” by B. Bonet et al., using the technique of net unfolding. This is an interesting paper that actually includes rigorous proofs to back up its ideas, as well as experimental results and benchmarks. Another mathematical paper that deals with unfolding is “McMillan’s Complete Prefix for Contextual Nets,” by P. Baldan et al. The ideas presented here also deserve more study.

Finally, the paper “Elasticity and Petri Nets,” by J. Cortadella et al., deals with time-elastic nets in which the clock is replaced by communication handshakes or augmented with a synchronous version of a handshake.