Web based IOPT Petri net Editor with an extensible plugin architecture to support generic net operations

The aim of this work is the modeling and verification of concurrent systems subject to dynamic changes using extensions of Petri nets. We begin by introducing the notion of net rewriting system. In a net rewriting system, a system configuration is described as a Petri net and a change in configuration is described as a graph rewriting rule. We show that net rewriting systems are Turing powerful, that is, the basic decidable properties of Petri nets are lost and, thus, automatic verification in not possible for this class. A subclass of net rewriting systems are reconfigurable Petri nets. In a reconfigurable Petri net, a change in configuration amounts to the modification of the flow relations of the places in the domain of the involved rule according to this rule, independently of the context in which this rewriting applies. We show that reconfigurable Petri nets are formally equivalent to Petri nets. This equivalence ensures that all the fundamental properties of Petri nets are still decidable for reconfigurable Petri nets and this model is thus amenable to automatic verification tools. Therefore, the expressiveness of both models is the same, but, with reconfigurable Petri nets, we can easily and directly model systems that change their structure dynamically.

We use the by now well established setting of modal semirings to derive a modal algebra for Petri nets. It is based on a relation-algebraic calculus for separation logic that enables calculations of properties in a pointfree fashion and at an abstract level. Basically, we start from an earlier logical approach to Petri nets that in particular uses modal box and diamond operators for stating properties about the state space of such a net. We provide relational translations of the logical formulas which further allow the characterisation of general behaviour of transitions in an algebraic fashion. From the relational structure an algebra for frequently used properties of Petri nets is derived. In particular, we give connections to typical used assertion classes of separation logic. Moreover, we demonstrate applicability of the algebraic approach by calculations concerning a standard example of a mutex net.

This paper describes the IOPT-Tools cloud-based tool-chain, offering a complete set of tools supporting design automation for embedded controller’s development, benefiting from adopting a model-driven development attitude. The tools are freely available online at http://gres.uninova.pt/IOPT-Tools/ . The tool-chain relies on IOPT nets (Input-Output Place-Transition nets) to describe the controller behavior, allowing an explicit representation of constraints on input and output signals and events, which is necessary for the development of controllers. The IOPT-Tools tool-chain includes tools for interactive graphical IOPT nets models editing, simulation and test (token-player, timing diagram, remote debugging), as well as a state-space generator, state-space visualization, and a query system for properties verification. The tool-chain also supports the automatic generation of execution code to be directly deployed in the controllers’ implementation platforms, such as FPGA boards, as well as Arduino, Raspberry, and other Linux-based boards. Most notably, it is possible to obtain C code and VHDL code to be directly deployed into the referred boards without writing/changing a line in the generated code. The tool-chain uses the PNML format for storing the models and can import PNML models generated by other frameworks, automatically generating, if necessary, an associated graphical representation. After, it is possible to add input and output signals and events to create controller models. IOPT-Tools also supports net operations, namely net addition, allowing composition of sub-models, and net splitting, which in conjunction with the use of clock domains and dedicated communication channels support the development of distributed controllers.

Petri nets are used as models of asynchronous concurrent systems. The underlying structure of a Petri net is a bipartite digraph. Many properties of Petri nets and the systems they model can be described in graph theoretic terms. These include the notions of deadlocks and traps. In this paper we consider these properties by restricting attention to some special classes of Petri nets including simple, complete, and free-choice Petri nets.

Petrinets are the suitable tool for modeling and analysis of discrete event systems. The effective methods of analyzing the discrete event systems (DES) are exhibited by Petri nets. The entire structure of the system is mathematically expressed using Petrinets and also all the properties are analysed by different methods. The properties of Petrinets are different in various systems, a Flexible Manufacturing System (FMS) requires production activities in which raw materials, energy, labour, and equipment are combined together in the modification process for the production of good quality goods.” The word “flexible” explains the capability of the system to relate productively to make changes in the system. These changes can be internal failure of the system or classification problems such as a sample or external changes in the structure of the model as well as demand for the process. The inherent limitations such as undecidable properties, complexity in checking, automatic verification of the modeled system are existing in FMS. This paper explains a study on FMS using Petri net reduction. A PN underlies event structures with casuality and compatibility relations. Partial order methods and reduction methods reduce the complexity of constructing the reachability graph. The determination of PN system through reduction methods in recent years focused by many researchers. The significance of reduction methods are highlighted to execute the faster analysis of a system. Instead of coverability trees and the graphical representation the incidence matrix of the PNs are used for the reduction methods. Reduction methods are used to simplify large scale PNs into “equivalent” smaller nets. Boundedness, liveness, simplification of implicit places, shared resources and elimination of self-loops are checked though equivalent smaller nets. The structure of FMS is preserved.

We consider Nested Petri nets (NP-nets), i.e. Petri nets in which tokens can be Petri nets themselves. To increase flexibility and give tools for modeling adaptive processes we extend this formalism by allowing operations on net tokens. We prove decidability of some crucial for verification problems and thus show that, in spite of very flexible structure, NP-nets maintain "good" properties of ordinary Petri nets.

The dynamic behavior of concurrent systems can be modeled and analyzed using Petri nets. Many approaches have been proposed to analyze the properties of Petri nets. Among them, reachability analysis is a fundamental method for studying the dynamic properties of Petri nets. However, state space explosion has obstructed its applicability for analyzing large-scale systems. This paper presents a new method to attack state space explosion based on the concept of compositional verification. The strength of our method is in preserving the global information of Petri nets and a set of more effective condensation rules especially for tightly coupled modules (subnets). The current version of our method provides an efficient analysis for detecting deadlock states. An extension of our method for detecting reachable markings is also described.

On Selected Properties of Uninorm Petri Nets and Their Application in Modeling Knowledge-Based Systems

In this paper, we investigate transition systems of a class of Petri nets suitable for the modelling and behavioural analysis of globally asynchronous locally synchronous systems. The considered model of Elementary Net Systems with Localities (ENL-systems) is basically that of Elementary Net Systems (EN-systems) equipped with an explicit notion of locality. Each locality identifies a distinct set of events which may only be executed synchronously, i.e., in a maximally concurrent manner. For this reason, the overall behaviour of an ENL-system cannot be represented by an interleaved transition system, with arcs being labelled by single events, but rather by a suitable notion of a step transition system, with arcs being labelled by sets of events executed concurrently.We completely characterise transition systems which can be generated by Elementary Net Systems with Localities under their intended concurrency semantics. In developing a suitable characterisation, we follow the standard approach in which key relationships between a Petri net and its transition system are established via the regions of the latter defined as specific sets of states of the transition system. We argue that this definition is insufficient for the class of transition systems of ENL-systems, and then augment the standard notion of a region with some additional information, leading to the notion of a region with explicit input and output events (or io-region).We define, and show consistency of, two behaviour preserving translations between ENL-systems and their transition systems. As a result, we provide a solution to the synthesis problem of Elementary Net Systems with Localities, which consists in constructing an ENL-system for a given transition system in such a way that the transition system of the former is isomorphic to the latter.KeywordsTheory of concurrencyPetri netselementary net systemslocalitiesanalysis and synthesisstep sequence semanticsstructure and behaviour of netstheory of regionstransition systems

Synthesis and verification of discrete control logic by a combined application of automata based supervisory control theory and Petri nets is addressed. While supervisory control theory is well suited to specification and design of the interlock part of the control logic, the sequencing part can be more easily described by Petri net models. The basic idea presented in the paper is to design basic interlock logic by the use of supervisory control theory and then to use the derived model of admissible behaviour as a process model. The sequencing part is designed in a form of a Petri net model which is verified against the process model. The basic property of interest is the absence of blocking. To study the interaction of the two models we use an extension of Place/Transition nets which includes external inputs and outputs, i.e., the Real-time Petri nets (RTPN). In order to verify the nonblocking of the controller a new kind of reachability analysis is proposed, which considers all possible changes of the controller input and output signals.

Most verification techniques for highly populated discrete systems suffer from the state explosion problem. The "fluidification" of discrete systems is a classical relaxation technique that aims to avoid the state explosion problem. Continuous Petri nets are the result of fluidifying traditional discrete Petri nets. In continuous Petri nets the firing of a transition is not constrained to the naturals but to the non-negative reals. Unfortunately, some important properties, as liveness, may not be preserved when the discrete net model is fluidified. Therefore, a thorough study of the properties of continuous Petri nets is required. This paper focuses on the study of deadlock-freeness in the framework of mono-T-semiflow continuous Petri nets, i.e., conservative nets with a single repetitive sequence (T-semiflow). The study is developed both on untimed and timed systems. Topological necessary conditions are extracted for this property. Moreover, a bridge relating deadlock-freeness conditions for untimed and timed systems is established

A set of necessary conditions for a Petri net to be plain, pure and safe is given. Some applications of these conditions both in practice (for Petri net synthesis), and in theory (e.g., as part of a characterisation of the reachability graphs of live and safe marked graphs) are described.

Many safety-critical real-time embedded systems need to meet stringent timing constraints such as preserving delay bounds between input and output events. In model-based development, a system is often implemented by using a code generator to automatically generate source code from system models, and integrating the generated source code with a platform. It is challenging to guarantee that the implemented systems preserve required timing constraints, because the timed behavior of the source code and the platform is closely intertwined. In this paper, we address this challenge by proposing a model transformation approach for the code generation. Our approach compensates the platform-processing delays by adjusting the timing parameters in system models, based on an Integer Linear Programming problem formulation. We demonstrate the usefulness of our approach via a case study of infusion pump systems. Experimental results show that the code generated using our approach can better preserve the timing constraints.

Petri nets are able to express the causality as well as the concurrency of a control algorithm. Signal interpreted Petri nets (SIPN) show good properties for model logic controllers. In SIPN the firing of a transition depends on input signals from the environment and the SIPN influences the environment via output signals. Since the function of a logic controller is basically determined by software, the question of software quality arises in this area. ISO/IEC 9126 defines six characteristics of software that can be used as quality criteria. In the six characteristics are set in the framework of controller design: the functionality and reliability of the software rely on the correctness of the algorithm. In this criteria for formal correctness of SIPN control algorithms are given, and it is shown how they can be evaluated using the SIPN reachability graph. Due to a close relation between sequential function chart (SFC) according to IEC 1131-3 standard [IEC 1992] and SIPN the criteria are also valid for SFC.

This paper deals with the verification of logic control system designs by signal interpreted Petri net (SIPN), which is a special extension of an ordinary Petri net (PN) by input and output signals. Such extensions provide more power for a specification. However, due to the extensions the basic Petri net analysis method is not strong enough to determine the properties. A model checking approach has been applied to the verification of an SIPN design. The requirements to be verified are expressed in temporal logic (TL). Via a model checking algorithm the validity of such requirements can be checked automatically in every possible input sequences. In an error case a sequence of states is calculated, which indicates a trace leading to the violation of the requirements. A case study has shown that this approach can effectively locate errors in the design process.