Model checking Petri nets with MSVL

This paper presents an approach to performing artificial intelligence planning through temporal logic programming with Search Control Knowledge (SCK). First, the planning problem described with Planning Domain Description Language is modeled as a program m in Modeling, Simulation and Verification Language (MSVL). Second, the SCK is also specified with an MSVL program $$m'$$ . Third, using the basic operation “and” in MSVL, a new MSVL program “ $$m~and~m'$$ ” is obtained. Forth, with the compiler MC of MSVL, an executable binary code of program “ $$m~and~m'$$ ” is obtained. Finally, planning result can be obtained via executing the executable code. Experimental results on selected benchmark planning domains from the International Planning Competition 2014 show that our approach is more effective in practice. Furthermore, the obtained plans are verified with the toolkit MSV so that a plan can be confirmed whether it is a reliable one.

This paper presents an approach to simulate and verify the CTCS-3 (Chinese Train Control System 3) protocol with a Modeling, Simulation and Verification Language (MSVL) which is an executable subset of Projection Temporal Logic (PTL). First, the syntax and semantics of PTL and MSVL are briefly introduced. Then, CTCS-3 protocol is briefly presented and a simplified CTCS-3 protocol described by an MSVL program is given, and the property to be verified is specified by a Propositional Projection Temporal Logic (PPTL) formula. Finally, the simulation is conducted by means of the interpreter of MSVL. A dynamic graph showing behavior of train is depicted. Based on the graph, we can verify whether or not the protocol satisfies the property.

To verify the correctness of Python programs, a novel approach for model checking Python programs with MSVL (Modeling, Simulation and Verification Language) is advocated. To this end, the rules for decoding the object-oriented semantics of Python with the process-oriented semantics of MSVL are defined, and the technique for automatically rewriting a Python program into its equivalent MSVL program is formalized, which in turn can be verified with the model checking tool MSV. In addition, an example is given to illustrate how the approach works. The approach fully utilizes the powerful expressiveness of MSVL to verify Python programs in a direct way, and helps to improve the quality of the software system.

This paper proposes an approach to verifying programs against context free properties. To this end, the system to be verified is modeled by a program m in Modeling, Simulation and Verification Language (MSVL), and the desired property is also specified by an MSVL program \(m'\). Then program m and formula \(\lnot m'\) are interpreted by means of executing programs m and \(m'\). If an acceptable execution path is generated, a counterexample is found, otherwise the property is valid. To show how the proposed approach works, an example is given.

A novel approach to verifying context free properties of programs

To solve the problem that UML (Unified Modeling Language) design model cannot be model-checked for its rough semantics, an extension of UML, called xUML4MC, is defined by extending the activity diagram with accurate syntax and semantics to model the activities of an object. Besides, the technique for automatical transformation of xUML4MC model into MSVL (Modeling, Simulation and Verification Language) model is also presented, which in turn can be verified with model checking tool MSV. The formalism arms the classical visual specification language UML with the power of model checking, and helps to promote the quality of software system.

Process versus unfolding semantics for Place/Transition Petri nets

We introduce infinitary partial languages for Petri nets and study some of their properties. Earlier results on the interrelation between various Petri net semantics for finite behaviour are shown to be valid for infinite behaviour. As a consequence step sequences and event structures of processes both can be taken as a semantics for Petri nets without any loss of information.Via the introduction of infinite partial words it is possible to express the properties of justice and fairness in a natural way: justice can be characterized as maximality of progress and fairness as ‘fair’ conflict resolution. By this we overcome the ambiguity arising from the lack of discrimination between concurrency and non-determinism in the sequential approach.

In order to model the behaviour of open concurrent systems by means of Petri nets, we introduce open Petri nets, a generalisation of the ordinary model where some places, designated as open, represent an interface between the system and the environment. Besides generalising the token game to reflect this extension, we define a truly concurrent semantics for open nets by extending the Goltz–Reisig process semantics of Petri nets. We introduce a composition operation over open nets, characterised as a pushout in the corresponding category, suitable for modelling both interaction through open places and synchronisation of transitions. The deterministic process semantics is shown to be compositional with respect to such a composition operation. If a net $Z_3$ results as the composition of two nets $Z_1$ and $Z_2$, having a common subnet $Z_0$, then any two deterministic processes of $Z_1$ and $Z_2$ that ‘agree’ on the common part, can be ‘amalgamated’ to produce a deterministic process of $Z_3$. Conversely, any deterministic process of $Z_3$ can be decomposed into processes of the component nets. The amalgamation and decomposition operations are shown to be inverse to each other, leading to a bijective correspondence between the deterministic processes of $Z_3$ and the pair of deterministic processes of $Z_1$ and $Z_2$ that agree on the common subnet $Z_0$. Technically, our result is similar to the amalgamation theorem for data-types in the framework of algebraic specification. A possible application field of the proposed constructions and results is the modelling of interorganisational workflows, recently studied in the literature. This is illustrated by a running example.

Understanding biological pathways is an important activity in the biological domain for drug development. Due to the parallelism and complexity inherent in pathways, computer models that can answer queries about pathways are needed. A researcher may ask `what-if' questions comparing alternate scenarios, that require deeper understanding of the underlying model. In this paper, we present overview of such a system we developed and an English-like high level language to express pathways and queries. Our language is inspired by high level action and query languages and it uses Petri Net execution semantics.

Efficient State Space Search for Time Petri Nets

In the paper, a "truly concurrent" and nondeterministic semantics is defined in terms of branching processes of discrete-time Petri nets (DTPNs). These nets may involve infinite numbers of transitions and places, infinite number of tokens in places, and (maximal) steps of concurrent transitions, which allows us to consider this class of DTPNs to be the most powerful class of Petri nets. It is proved that the unfolding (maximal branching process) of the DTPN is the greatest element of a complete lattice constructed on branching processes of DTPNs with step semantics. Moreover, it is shown that this result is true also in the case of maximal transition steps if additional restrictions are imposed on the structure and behavior of the DTPN.

We propose rewriting logic as a unifying framework for a wide range of nets models. We treat in detail place/transition nets and important extensions of the basic model by individual tokens, test arcs, and time. Based on the idea that Petri nets are monoids suggested by Meseguer and Montanari we define a rewriting semantics that maps place/transition nets into rewriting logic specifications. We furthermore generalize this result to a general form of algebraic net specifications subsuming also colored nets as a special case. The soundness and completeness results we state relate the commutative process semantics of nets proposed by Best and Devillers to the model-theoretic semantics of rewriting logic in the sense of natural isomorphisms between suitable functors. In addition we show how place/transition nets with test arcs and timed nets can be equipped with a rewriting semantics and discuss how other extensions can be treated along similar lines. Beyond the conceptual unification of quite different kinds of nets within a single framework, the rewriting semantics can provide a guide for future extensions of nets and help to cope with the growing diversity of models in this field. On the practical side, a major application of the rewriting semantics is its use as a logical and operational representation of net models for formal verification and for the efficient execution and analysis using a rewriting engine such as Maude, which also allows us to specify different execution and analysis strategies in the same rewriting logic language by means of reflection.

Specification and properties of a cache coherence protocol model.- GAMERU: A language for the analysis and design of human communication pragmatics within organizational systems.- Recent results on the complexity of problems related to Petri nets.- Algebraic structure of flows of a regular coloured net.- On equivalent execution semantics of concurrent systems.- Mathematical methods for calculating invariants in Petri nets.- On Petri nets with deterministic and exponentially distributed firing times.- An accurate performance model of CSMA/CD bus LAN.- Petri net models for the ?-calculus.- Fair processes.- Operational Petri net semantics for CCSP.- Infinitary languages of Petri nets and logical sentences.- A strong part of concurrency.- Concurrency and continuity.- Parallel systems specifications with coloured Petri nets and algebraic specifications.- Bibliography of Petri nets.

A general stochastic hybrid process (GSHP) is a mathematical formalism that covers most of the requirements posed by the modelling of complex operations, such as time dependencies, multi-dimensional continuous as well as discrete processes, discontinuities, randomness and model uncertainties. In addition, it is possible to study GSHP by using stochastic analysis methodologies, thereby empowering it with powerful mathematical properties. This guarantees unambiguous simulation possibility of the model and allows speeding up this simulation while keeping the model properties intact. However, using GSHP to construct a model of a complex operation is not easy. To support the modelling and the subsequent verification both by mathematical and by multiple operational domain experts, a supporting graphical modelling formalism is desired. Petri nets have shown to be useful for developing models of various complex applications. Typical Petri net features are concurrency and synchronisation mechanism, hierarchical and modular construction, and natural expression of causal dependencies, in combination with graphical and analytical representations. The aim of this thesis is to combine the strengths of Petri net modelling formalisms and those of GSHP. First, dynamically coloured Petri nets (DCPN) are developed, and proof of equivalence is provided with piecewise deterministic Markov processes, which is a particular class of GSHP. Next, DCPN are extended to stochastically and dynamically coloured Petri nets (SDCPN), and proof of equivalence is provided with GSHP. Subsequently, SDCPN are extended to SDCPN with interconnection mapping types (SDCPNimt) and proof of equivalence is provided with both SDCPN and GSHP. It is shown with illustrative air transport examples that these three classes of Petri net are very effective when it comes to the compositional modelling of operations consisting of many distributed components that behave and interact in a dynamic way with many uncertainties. With the equivalence relations between these formalisms, the properties and strengths of the various approaches are combined. The many applications of the approach developed in this thesis, executed at NLR and beyond, show that both the approach and its combined strengths are acknowledged and supported by practice.