Showing papers on "Process architecture published in 2007"

Petri net modelling of biological networks

Abstract: Mathematical modelling is increasingly used to get insights into the functioning of complex biological networks. In this context, Petri nets (PNs) have recently emerged as a promising tool among the various methods employed for the modelling and analysis of molecular networks. PNs come with a series of extensions, which allow different abstraction levels, from purely qualitative to more complex quantitative models. Noteworthily, each of these models preserves the underlying graph, which depicts the interactions between the biological components. This article intends to present the basics of the approach and to foster the potential role PNs could play in the development of the computational systems biology.

A Time Petri Net Extended with Price Information

Abstract: Performance and cost analysis are the two main purposes of business process modeling, where the Petri net extended with time information is an effective tool for performance analysis, but not for cost analysis. This paper proposes a time Petri net extended with price information—Price Time Petri Net. Firstly, this paper associates a price with a time transition, and gives the semantics for price time Petri net in terms of priced timed transition systems. Then it defines a priced state class as an extension of state class, and discusses the soundness and completeness for this extension. An algorithm is given to prove that the minimum-cost reachability problem for bounded price time Petri net is decidable. Finally, this paper gives an example and draws a conclusion that incorporating price information in time Petri net and applying price time Petri net to business process management

Process mining based on regions of languages

Abstract: In this paper we give an overview, how to apply region based methodsfor the synthesis of Petri nets from languages to process mining The research domain of process mining aims at constructing a process modelfrom an event log, such that the process model can reproduce the log, and doesnot allow for much more behaviour than shown in the log We here considerPetri nets to represent process models Event logs can be interpreted as finite languagesRegion based synthesis methods can be used to construct a Petri net froma language generating the minimal net behaviour including the given languageTherefore, it seems natural to apply such methods in the process mining domainThere are several different region based methods in literature yielding differentPetri nets We adapt these methods to the process mining domain and comparethem concerning efficiency and usefulness of the resulting Petri net

Distributed Diagnosis of Place-Bordered Petri Nets

Abstract: This paper studies online fault detection and isolation of modular dynamic systems modeled as sets of place-bordered Petri nets. The common places among the set of Petri nets modeling a system capture coupling of various system components. The transitions are labeled by events, some of which are unobservable (i.e., not directly recorded by the sensors attached to the system). The events whose occurrence must be diagnosed have unobservable transition labels. These events model faults or other significant changes in the system state. The existing theory of diagnosis of discrete-event systems is extended in the context of the above model. The modular structure of the system is exploited by a distributed algorithm for fault diagnosis. A Petri net diagnoser is associated with every Petri net and the diagnosers communicate in real time during the diagnostic process when the token count of common places changes. A merge function is defined to combine the individual diagnoser states and recover the complete diagnoser state that would be obtained under a monolithic approach. Strategies that reduce the communication overhead are presented. The software implementation of the distributed algorithm is discussed. Note to Practitioners-In the last decade, monitoring, fault detection, and diagnosis methodologies based on the use of discrete-event models have been successfully used in a variety of technological systems ranging from document processing systems to intelligent transportation systems. This paper was motivated by the problem of fault diagnosis for modular (distributed) dynamic discrete-event systems (DES). As a DES modeling formalism, Petri nets offer potential advantages in terms of the distributed representation of the system and the ability to represent coupling of the system components. The systems studied in this paper are sets of modules coupled with each other through various system components and modeled using Petri nets. We present a distributed fault diagnosis algorithm which allows each module in the distributed system to diagnose its faults independently unless completion of a task requires the use of coupled components. In the case of coupling, modules communicate with each other to accurately diagnose the fault. The distributed fault diagnosis algorithm recovers the monolithic diagnosis information at the cost of communication and growing communication overhead. To mitigate that problem, we present an improved version of the algorithm that significantly reduces the communication overhead. Finally, we introduce the software toolbox (written in Matlab and integrated with AT&T Graphviz) and we present a case study of an example of a heating, ventilation, and air-conditioning system where we use the software tool for modeling and analyzing the system

The Input-Output Place-Transition Petri Net Class and Associated Tools

Abstract: Petri nets are a well-known formalism widely used in different application areas. Yet, the lack of adequate tools that can be integrated within engineering development frameworks are one major drawback. This paper identifies and justifies the characteristics of one class of Petri nets targeted for the modelling of automation systems and (networked) embedded systems, named as input-output Petri net (IOPT), and its representation using the Petri net markup language (PNML). The paper also presents a set of associated tools under development. This Petri net class, defined on top of the well-known place-transition Petri nets, is the common link across a set of tools under development, including a graphical editor, a state-space analyser for the verification of properties, conflict resolution through automatic arbiter generation, automatic code generators, simulator, among others. In this sense, the main goal of the proposed Petri net class and associated tools is to support the entire system development flow, from specification to implementation.

Introduction to generalized stochastic Petri nets

Abstract: Generalized Stochastic Petri Nets are a modelling formalism that can be conveniently used for the analysis of complex models of Discrete Event Dynamic Systems and for their performance and reliability evaluation. The automatic construction of the probabilistic models that underly the dynamic behaviours of these nets rely on a set of results that derive from the theory of untimed Petri nets. The paper briefly surveys some results of net theory together with the different approaches used to introduce the concept of time in these models that are useful for the definition of Stochastic Petri Nets and Generalized Stochastic Petri Nets. Details on the solution techniques and on their computational aspects are provided. A brief overview of advanced material is included at the end of the paper to highlight the state of the art in this field and to give pointers to relevant results published in the literature.

A unifying framework for modelling and analysing biochemical pathways using Petri nets

Abstract: We give a description of a Petri net-based framework for modelling and analysing biochemical pathways, which unifies the qualitative, stochastic and continuous paradigms. Each perspective adds its contribution to the understanding of the system, thus the three approaches do not compete, but complement each other. We illustrate our approach by applying it to an extended model of the three stage cascade, which forms the core of the ERK signal transduction pathway. Consequently our focus is on transient behaviour analysis. We demonstrate how qualitative descriptions are abstractions over stochastic or continuous descriptions, and show that the stochastic and continuous models approximate each other. A key contribution of the paper consists in a precise definition of biochemically interpreted stochastic Petri nets. Although our framework is based on Petri nets, it can be applied more widely to other formalisms which are used to model and analyse biochemical networks.

Definition of an Executable SPEM 2.0

Abstract: One major advantage of executable models is that once constructed, they can be run, checked, validated and improved in short incremental and iterative cycles. In the field of software process modeling, process models have not yet reached the level of precision that would allow their execution. Recently the OMG issued a new revision of its standard for software process modeling, namely SPEM2.0. However, even if executability was defined as a mandatory requirement in the RFP (request for proposal), the adopted specification does not fulfill it. This paper presents a critical analysis on the newly defined standard and addresses its lacks in terms of executability. An approach is proposed in order to extend the standard with a set of concepts and behavioural semantics that would allow SPEM2.0 process models to be checked through a mapping to Petri nets and monitored through a transformation into BPEL.

Petri Nets for Dynamic Event-Driven System Modeling

Abstract: Monmouth University 24.

Generating Petri net state spaces

Abstract: Most specific characteristics of (Place/Transition) Petri nets can be traced back to a few basic features including the monotonicity of the enabling condition, the linearity of the firing rule, and the locality of both. These features enable "Petri net" analysis techniques such as the invariant calculus, the coverability graph technique, approaches based on unfolding, or structural (such as siphon/trap based) analysis. In addition, most verification techniques developed outside the realm of Petri nets can be applied to Petri nets as well. In this paper, we want to demonstrate that the basic features of Petri nets do not only lead to additional analysis techniques, but as well to improved implementations of formalism-independent techniques. As an example, we discuss the explicit generation of a state space. We underline our arguments with some experience from the implementation and use of the Petri net based state space tool LoLA.

Sealing OS processes to improve dependability and safety

Abstract: In most modern operating systems, a process is a hardware-protected abstraction for isolating code and data. This protection, however, is selective. Many common mechanisms---dynamic code loading, run-time code generation, shared memory, and intrusive system APIs---make the barrier between processes very permeable. This paper argues that this traditional open process architecture exacerbates the dependability and security weaknesses of modern systems.As a remedy, this paper proposes a sealed process architecture, which prohibits dynamic code loading, self-modifying code, shared memory, and limits the scope of the process API. This paper describes the implementation of the sealed process architecture in the Singularity operating system, discusses its merits and drawbacks, and evaluates its effectiveness. Some benefits of this sealed process architecture are: improved program analysis by tools, stronger security and safety guarantees, elimination of redundant overlaps between the OS and language runtimes, and improved software engineering.Conventional wisdom says open processes are required for performance; our experience suggests otherwise. We present the first macrobenchmarks for a sealed-process operating system and applications. The benchmarks show that an experimental sealed-process system can achieve performance competitive with highly-tuned, commercial, open-process systems.

Identification of Petri Nets from Knowledge of Their Language

Abstract: In this paper we deal with the problem of identifying a Petri net system, given a finite language generated by it. First we consider the problem of identifying a free labeled Petri net system, i.e., all transition labels are distinct. The set of transitions and the number of places is assumed to be known, while the net structure and the initial marking are computed solving an integer programming problem. Then we extend this approach in several ways introducing additional information about the model (structural constraints, conservative components, stationary sequences) or about its initial marking. We also treat the problem of synthesizing a bounded net system starting from an automaton that generates its language. Finally, we show how the approach can also be generalized to the case of labeled Petri nets, where two or more transitions may share the same label. In particular, in this case we impose that the resulting net system is deterministic. In both cases the identification problem can still be solved via an integer programming problem.

Reachability Problems and Abstract State Spaces for Time Petri Nets with Stopwatches

Abstract: Several extensions of Time Petri nets (TPNs) have been proposed for modeling suspension and resumption of actions in timed systems. We first introduce a simple class of TPNs extended with stopwatches (SwTPNs), and present a semi-algorithm for building exact representations of the behavior of SwTPNs, based on the known state class method for Time Petri nets. Then, we prove that state reachability in SwTPNs and all similar models is undecidable, even when bounded, which solves an open problem. Finally, we discuss overapproximation methods yielding finite abstractions of their behavior for a subclass of bounded SwTPNs, and propose a new one based on a quantization of the polyhedra representing temporal information. By adjusting a parameter, the exact behavior can be approximated as closely as desired. The methods have been implemented, experiments are reported.

Modeling and analysis of multi-agent systems using petri nets

Abstract: The development of theoretical-based methods for the assessment of multi-agent systems properties is of critical importance. This work is a preliminary investigation on methodologies for modeling, analysis and design of multi-agent systems. Multi-agent systems are regarded as discrete-event dynamic systems and Petri nets are used as a modeling tool to assess the structural properties of the multi-agent system. Our methodology consists of defining a simple multi-agent system based on the abstract architecture for intelligent agents. The abstract architecture is modeled as a discrete-event system using Petri nets and structural analysis of the net provides an assessment of the communication and coordination properties of the multi-agent system. Deadlock avoidance in the multi-agent system is considered as an initial key property, and it is evaluated using liveness and boundedness properties of the Petri net model.

How to synthesize nets from languages: a survey

Abstract: In this paper we present a survey on methods for the synthesis of Petri nets from behavioral descriptions given as languages. We consider place/transition Petri nets, elementary Petri nets and Petri nets with inhibitor arcs. For each net class we consider classical languages, step languages and partial languages as behavioral description. All methods are based on the notion of regions of languages. We identify two different types of regions and two different principles of computing from the set of regions of a language a finite Petri net generating this language. For finite or regular languages almost each combination of Petri net class, language type, region type and computation principle can be considered to compute such a net. Altogether, we present a framework for region-based synthesis of Petri nets from languages which integrates almost all known approaches and fills several remaining gaps in literature.

Planning via Petri net unfolding

Abstract: The factored state representation and concurrency semantics of Petri nets are closely related to those of concurrent planning domains, yet planning and Petri net analysis have developed independently, with minimal and usually unconvincing attempts at cross-fertilisation. In this paper, we investigate and exploit the relationship between the two areas, focusing on Petri net unfolding, which is an attractive reachability analysis method as it naturally enables the recognition and separate resolution of independent subproblems. On the one hand, based on unfolding, we develop a new forward search method for cost-optimal partial-order planning which can be exponentially more efficient than state space search. On the other hand, inspired by well-known planning heuristics, we investigate the automatic generation of heuristics to guide unfolding, resulting in a more efficient, directed reachability analysis tool for Petri nets.

Introducing the modeling and verification process in SysML

Abstract: The development process of complex systems needs to take in account differents domains and aspects. SysML (Systems Modeling Language) is a new modeling language that allows a system description with various integrated diagrams (as structure, behavior and requirements diagrams), but SysML lacks formality for the requirement verification. The aim of this paper is to propose an approach to verify complex systems using SysML as a language which describes the system structure and requirements. Petri nets and temporal logic LTL are used respectively to formalize the system behavior and requirements. The benefit of such formalization is to allow an automatic formal verification. In order to demonstrate this methodology, it will be used a factory automation system, modeled by SysML and Petri nets, and verified by the TINA toolbox.

Recursive Petri nets: Theory and application to discrete event systems

Abstract: In order to design and analyse complex systems, modelers need formal models with two contradictory requirements: a high expressivity and the decidability of behavioural property checking. Here we present and develop the theory of such a model, the recursive Petri nets. First, we show that the mechanisms supported by recursive Petri nets enable to model patterns of discrete event systems related to the dynamic structure of processes. Furthermore, we prove that these patterns cannot be modelled by ordinary Petri nets. Then we study the decidability of some problems: reachability, finiteness and bisimulation. At last, we develop the concept of linear invariants for this kind of nets and we design efficient computations specifically tailored to take advantage of their structure.

Model checking bounded prioritized time Petri nets

Abstract: In a companion paper [BPV06], we investigated the expressiveness of Time Petri Nets extended with Priorities and showed that it is very close to that Timed Automata, in terms of weak timed bisimilarity. As a continuation of this work we investigate here the applicability of the available state space abstractions for Bounded Time Petri Nets to Bounded Prioritized Time Petri Nets. We show in particular that a slight extension of the "strong state classes" construction of [BV03] provides a convenient state space abstraction for these nets, preserving markings, states, and LTL formulas. Interestingly, and conversely to Timed Automata, the construction proposed does not require to compute polyhedra differences.

Dense-timed petri nets: checking zenoness, token liveness and boundedness

Abstract: We consider Dense-Timed Petri Nets (TPN), an extension of Petri nets in which each token is equipped with a real-valued clock and where the semantics is lazy (i.e., enabled transitions need not fir ...

A Model-Based Approach for Testing GUI Using Hierarchical Predicate Transition Nets

Abstract: Testing graphical user interface (GUI) has shown to be costly and difficult. Existing approaches for testing GUI are event-driven. In this paper, we propose a model based testing method to test the structural representation of GUIs specified in high class of Petri nets known as hierarchical predicate transitions nets (HPrTNs). In order to detect early design faults and fully benefit from HPrTNmodels, we have extended the original coverage criteria proposed for HPrTNs by event-based criteria defined for GUI testing

Well-structured languages

Abstract: This paper introduces the notion of well-structured language. A well-structured language can be defined by a labelled well-structured transition system, equipped with an upward-closed set of accepting states. That peculiar class of transition systems has been extensively studied in the field of computer-aided verification, where it has direct an important applications. Petri nets, and their monotonic extensions (like Petri nets with non-blocking arcs or Petri nets with transfer arcs), for instance, are special subclasses of well-structured transition systems. We show that the class of well-structured languages enjoy several important closure properties. We propose several pumping lemmata that are applicable respectively to the whole class of well-structured languages and to the classes of languages recognized by Petri nets or Petri nets with non-blocking arcs. These pumping lemmata allow us to characterize the limits in the expressiveness of these classes of language. Furthermore, we exploit the pumping lemmata to strictly separate the expressive power of Petri nets, Petri nets with non-blocking arcs and Petri nets with transfer arcs.

Process mining and verification

Abstract: ion of the process under consideration. Examples of properties that check whether that is the case are: that every case that is started should be finished at some point, or that no case can result in a undesired state. In this chapter, we introduce techniques to check such properties on a process model. More precisely, we introduce process model verification, as shown in Figure 5.1.

Story manager in 'Europe 2045' uses Petri nets

Abstract: Europe 2045 is an on-line multi-player strategy game aimed at education of high-school students in economics, politics, and media studies. The essential feature of the game is that players face various simulated scenarios and crises addressing contemporary key issues of the unified Europe. These scenarios are branching and can evolve in a parallel manner. In this paper, we present a technique for specifying plots of these scenarios, which underpins the story manager of Europe 2045. The technique is based on a modification of Petri Nets. We also detail one particular scenario concerning the current crisis in Darfur. On a general level this paper discusses the strengths and weaknesses of implementation of Petri Nets in virtual storytelling.

Automatic generation of simulation models for semiconductor manufacturing

Abstract: This article gives an overview of a framework for automatically generating large-scale simulation models from a domain specific problem definition data schema, here semiconductor manufacturing. This simulation model uses an object-oriented Petri net data structure. The Petri net based simulation uses the same enabling rules as classical Petri nets, but has extensions of time and priorities. This approach minimizes the effort of model verification. Each object identified in the problem data specification is mapped to corresponding Petri net fragments. The Petri net simulation model is synthesized from verifiable subnets. This allows ensuring the liveness of the final Petri net simulation model. The applicability of this approach is demonstrated by generating a simulation model based on the Sematech data set.

Continuous Petri nets: expressive power and decidability issues

Abstract: State explosion is a fundamental problem in the analysis and synthesis of discrete event systems. Continuous Petri nets can be seen as a relaxation of discrete models. The expected gains are twofold: improvements in comlexity and in decidability. This paper concentrates on the study of decidability issues. In the case of autonomous nets it is proved that properties like reachability, liveness or deadlock-freeness remain decidable. When time is introduced in the model (using an infinite server semantics) decidability of these properties is lost, since continuous timed Petri nets are able to simulate Turing machines.