Showing papers on "Petri net published in 2001"

Deadlock avoidance in sequential resource allocation systems with multiple resource acquisitions and flexible routings

Abstract: Considers the deadlock avoidance problem for the class of conjunctive/disjunctive (sequential) resource allocation systems (C/D-RAS), which allows for multiple resource acquisitions and flexible routings. First, a siphon-based characterization for the liveness of Petri nets (PNs) modeling C/D-RAS is developed, and subsequently, this characterization facilitates the development of a polynomial-complexity deadlock avoidance policy (DAP) that is appropriate for the considered RAS class. The resulting policy is characterized as C/D-RUN. The last part of the paper exploits the aforementioned siphon-based characterization of C/D-RAS liveness, in order to develop a sufficiency condition for C/D-RAS liveness that takes the convenient form of a mixed integer programming (MIP) formulation. The availability of this MIP formulation subsequently allows the "automatic" correctness verification of any tentative C/D-RAS DAP for which the controlled system behavior remains in the class of PNs modeling C/D-RAS, and the effective flexibility enhancement of the aforementioned C/D-RUN DAP implementations. Finally, we notice that, in addition to extending and complementing the current theory on deadlock-free sequential resource allocation to the most powerful class of C/D-RAS, the presented results also (i) nontrivially generalize important concepts and techniques of ordinary PN structural analysis to the broader class of nonordinary PNs, while (ii) from a practical standpoint, they can find direct application in the (work-) flow management of modern production, service and/or transportation environments.

Deadlock prevention policy based on Petri nets and siphons

Abstract: This paper presents a deadlock prevention method for a class of flexible manufacturing systems where deadlocks are caused by unmarked siphons in their Petri net models. This method is an iterative approach consisting of two main stages. At each iteration, a fast deadlock detection technique developed by mixed integer programming is used to find an unmarked maximal siphon. An algorithm is formalized that can efficiently obtain an unmarked minimal siphon from the maximal siphon. The first stage, called siphons control, of the proposed method is to add, for each unmarked minimal siphons, a control place to the original net with its output arcs to the sink transitions of the minimal siphon. The objective is to prevent a minimal siphon from being unmarked. The second stage, called augmented siphons control, is to add a control place to the modified net with its output arcs to the source transitions of the resultant net if the resource places are removed. The second stage is required since adding control places...

On Hybrid Petri Nets

Abstract: Petri nets (PNs) are widely used to model discrete event dynamic systems (computer systems, manufacturing systems, communication systems, etc). Continuous Petri nets (in which the markings are real numbers and the transition firings are continuous) were defined more recently; such a PN may model a continuous system or approximate a discrete system. A hybrid Petri net can be obtained if one part is discrete and another part is continuous. This paper is basically a survey of the work of the authors' team on hybrid PNs (definition, properties, modeling). In addition, it contains new material such as the definition of extended hybrid PNs and several applications, explanations and comments about the timings in Petri nets, more on the conflict resolution in hybrid PNs, and connection between hybrid PNs and hybrid automata. The paper is illustrated by many examples.

Verification on Infinite Structures

Abstract: In this chapter, we present a hierarchy of infinite-state systems based on the primitive operations of sequential and parallel composition; the hierarchy includes a variety of commonly-studied classes of systems such as context-free and pushdown automata, and Petri net processes. We then examine the equivalence and regularity checking problems for these classes, with special emphasis on bisimulation equivalence, stressing the structural techniques which have been devised for solving these problems. Finally, we explore the model checking problem over these classes with respect to various linear- and branching-time temporal logics.

Avoiding deadlock and reducing starvation and blocking in automated manufacturing systems

Abstract: Deadlock-free operations of automated manufacturing systems (AMS) are essential for high machine utilization and productivity. Based on the resource-oriented Petri net models of AMS and our previous work (2000) on a necessary and sufficient condition for deadlock-free operation, this paper proposes a new control policy such that it can avoid deadlock completely, and reduce starvation and blocking situations significantly. It attempts to release an appropriate number of jobs into the system and control the order of resource usage based on the state information in the net model. The theoretical results for the correctness of this policy are presented. An AMS allowing routing flexibility and varying operation times is used to demonstrate the potential of the proposed policy.

Exterminating the Dynamic Change Bug: A Concrete Approach to Support Workflow Change

Abstract: Adaptability has become one of the major research topics in the area of workflow management. Today's workflow management systems have problems dealing with both ad-hoc changes and evolutionary changes. As a result, the workflow management system is not used to support dynamically changing workflow processes or the workflow process is supported in a rigid manner, i.e., changes are not allowed or handled outside of the workflow management system. In this paper, we focus on a notorious problem caused by workflow change: the “dynamic change bug” (Ellis et al.s Proceedings of the Conference on Organizational Computing Systems, Milpitas, California, ACM SIGOIS, ACM Press, New York, 1995, pp. 10–21). The dynamic change bug refers to errors introduced by migrating a case (i.e., a process instance) from the old process definition to the new one. A transfer from the old process to the new process can lead to duplication of work, skipping of tasks, deadlocks, and livelocks. This paper describes an approach for calculating a safe change region. If a case is in such a change region, the transfer is postponed.

Timed Petri Nets and BQOs

Abstract: We consider (unbounded) Timed Petri Nets (TPNs) where each token is equipped with a real-valued clock representing the "age" of the token. Each arc in the net is provided with a subinterval of the natural numbers, restricting the ages of the tokens travelling the arc. We apply a methodology developed in [AN00], based on the theory of better quasi orderings (BQOs), to derive an efficient constraint system for automatic verification of safety properties for TPNs. We have implemented a prototype based on our method and applied it for verification of a parametrized version of Fischer's protocol.

Timed Petri nets in modeling and analysis of cluster tools

Abstract: Timed Petri nets are used as models of cluster tools representing the flow of wafers through the chambers of the tool as well as sequences of actions performed by the robotic transporter. Since the durations of all activities are also represented in the model, performance characteristics can be derived from the model for steady-state, as well as transient behaviors. The performance of single-blade tools is compared with that of dual-blade tools. The effects of multiple loadlocks, redundant chambers and multiple robots are discussed and, analyzed. Modeling of wafer routings with chamber revisiting and processing of wafers of multiple types is also briefly discussed.

What Is a Petri Net

Abstract: The increasing number of Petri net variants naturally leads to the question whether the term "Petri net" is more than a common name for very different concepts. This contribution tries to identify aspects common to all or at least to most Petri nets. It concentrates on those features where Petri nets significantly differ from other modeling languages, i.e. we ask where the use of Petri nets leads to advantages compared to other languages. Different techniques that are usually comprised under the header "analysis" are distinguished with respect to the analysis aim. Finally, the role of Petri nets in the development of distributed systems is discussed.

Relaxed Soundness of Business Processes

Abstract: Business processes play a central role in the reorganization of a company and the (re)design of the respective information system(s). Typically the processes are described with the help of a semiformal, graphical language such as the Event-driven Process Chains (EPCs) by Scheer. This approach provides a suitable medium for the communication between the participants: the domain experts and the IT specialists. But these models leave room for interpretation and hence ambiguities which makes them less suitable as a basis for the design of information systems. To remedy this we suggest to transform the EPCs into a formal representation (Petri nets) preserving the ambiguities, i.e. all possibly intended behaviour. Now formal techniques can be used to find out whether the possible behaviours comprise sensible behaviour. If so, we call the net relaxed sound. By not limiting the modeler compared to previous ways (e.g. [8], [3]) we take a pragmatic approach to correctness which only requires that the net represents some valid behaviour. This allows us to draw conclusions on mistakes in the original EPC and to make suggestions for its improvement thereby enhancing both the model's quality and its suitability for software engineering.

Markov regenerative stochastic petri nets to model and evaluate phased mission systems dependability

Abstract: This study deals with model-based dependability transient analysis of phased mission systems. A review of the studies in the literature showed that several aspects of multiphased systems pose challenging problems to the dependability evaluation methods and tools. To attack the weak points of the state-of-the-art we propose a modeling methodology that exploits the power of the class of Markov regenerative stochastic Petri net models. By exploiting the techniques available in the literature for the analysis of the Markov Regenerative Processes, we obtain an analytical solution technique with a low computational complexity, basically dominated by the cost of the separate analysis of the system inside each phase. Last, the existence of analytical solutions allows us to derive the sensitivity functions of the dependability measures, thus providing the dependability engineer with additional means for the study of phased mission systems.

Petri net algebra

Abstract: This book presents a step-by-step development of a rigorous framework for the specification and verification of concurrent systems. Petri Net Algebra takes its inspiration and methods from Process Algebra and Petri Nets, two prominent branches of concurrency theory. Added synergistic benefit is derived from combining their respective advantages. Petri nets are treated as composable objects, and as such they are embedded in a general process algebra. A generic process algebra is given an automatic Petri net semantics so that net-based verification techniques, based on structural invariants and causal partial orders, can be applied to the process algebra. Finally, the theory is applied to a realistic concurrent programming language. The book contains full proofs, carefully chosen examples and several possible directions for further research. A unique aspect is that the development of the Petri net algebra is handled so as to allow for further applications-oriented extensions and modifications.

Executable Petri net models for the analysis of metabolic pathways

Abstract: Computer-assisted simulation of biochemical processes is a means to augment the knowledge about the control mechanisms of such processes in particular organisms. This knowledge can be helpful for the goal-oriented design of drugs. Normally, continuous models (differential equations) are chosen for modelling such processes. The application of discrete event systems such as Petri nets has been restricted in the past to low-level modelling and qualitative analysis. To demonstrate that Petri nets are indeed suitable for simulating metabolic pathways, the glycolysis and citric acid cycle are selected as well-understood examples of enzymatic reaction chains (metabolic pathways). The paper discusses the steps that lead from gaining necessary knowledge about the involved enzymes and substances, to establishing and tuning high-level net models, to performing a series of simulations, and finally to analysing the results. We show that the consistent application of the Petri net view to these tasks has certain advantages, and – using advanced net tools – reasonable simulation times can be achieved.

Concurrent object-oriented programming and petri nets: advances in petri nets

Abstract: Section I.- Object Oriented Modelling with Object Petri Nets.- Using Petri Nets for Specifying Active Objects and Generative Communication.- Object-Oriented Nets with Algebraic Specifications: The CO-OPN/2 Formalism.- CLOWN as a Testbed for Concurrent Object-Oriented Concepts.- Concurrency in Communicating Object Petri Nets.- Object Orientation in Hierarchical Predicate Transition Nets.- CoOperative Objects: Principles, Use and Implementation.- OB(PN)2: An Object Based Petri Net Programming Notation.- On Formalizing UML with High-Level Petri Nets.- Section II.- Modeling a Groupware Editing Tool with Cooperative Objects.- Modelling Constrained Geometric Objects with OBJSA Nets.- An Object-Based Modular CPN Approach: Its Application to the Specification of a Cooperative Editing Environment.- KRON: Knowledge Engineering Approach Based on the Integration of CPNs with Objects.- Modeling of a Library with THORNs.- Inheritance of Dynamic Behavior Development of a Groupware Editor.- Object Coloured Petri Nets - A Formal Technique for Object Oriented Modelling.- Section III.- An Actor Algebra for Specifying Distributed Systems: The Hurried Philosophers Case Study.- Formal Reasoning about Actor Programs Using Temporal Logic.- Flexible Types for a Concurrent Model.- High Level Transition Systems for Communicating Agents.- Schedulability Analysis of Real Time Actor Systems Using Coloured Petri Nets.- Control Properties in Object-Oriented Specifications.- Case Studies.- A Cooperative Petri Net Editor.- The Hurried Philosophers.

Zero-suppressed BDDs and their applications

Abstract: In many real-life problems, we are often faced with manipulating sets of combinations. In this article, we study a special type of ordered binary decision diagram (OBDD), called zero-suppressed BDDs (ZBDDs). This data structure represents sets of combinations more efficiently than using original OBDDs. We discuss the basic data structures and algorithms for manipulating ZBDDs in contrast with the original OBDDs. We also present some practical applications of ZBDDs, such as solving combinatorial problems with unate cube set algebra, logic synthesis methods, Petri net processing, etc. We show that a ZBDD is a useful option in OBDD techniques, suitable for a part of the practical applications.

A Sweep-Line Method for State Space Exploration

Abstract: We present a state space exploration method for on-the-fly verification. The method is aimed at systems for which it is possible to define a measure of progress based on the states of the system. The measure of progress makes it possible to delete certain states on-the-fly during state space generation, since these states can never be reached again. This in turn reduces the memory used for state space storage during the task of verification. Examples of progress measures are sequence numbers in communication protocols and time in certain models with time. We illustrate the application of the method on a number of Coloured Petri Net models, and give a first evaluation of its practicality by means of an implementation based on the DESIGN/CPN state space tool. Our experiments show significant reductions in both space and time used during state space exploration. The method is not specific to Coloured Petri Nets but applicable to a wide range of modelling languages.

Contextual Petri nets, asymmetric event structures, and processes

Abstract: We present an event structure semantics for contextual nets, an extension of P/T Petri nets where transitions can check for the presence of tokens without consuming them (read-only operations). A basic role is played by asymmetric event structures, a generalization of Winskel's prime event structures where symmetric conflict is replaced by a relation modelling asymmetric conflict or weak causality, used to represent a new kind of dependency between events arising in contextual nets. Extending Winskel's seminal work on safe nets, the truly concurrent event-based semantics of contextual nets is given at categorical level via a chain of coreflections leading from the category SW-CN of semi-weighted contextual nets to the category Dom of finitary prime algebraic domains. First an unfolding construction generates from a contextual net a corresponding occurrence contextual net, from where an asymmetric event structure is extracted. Then the configurations of the asymmetric event structure, endowed with a suitable order, are shown to form a finitary prime algebraic domain. We also investigate the relation between the proposed unfolding semantics and several deterministic process semantics for contextual nets in the literature. In particular, the domain obtained via the unfolding is characterized as the collection of the deterministic processes of the net endowed with a kind of prefix ordering. 2001 Elsevier Science.

On formalizing UML with high-level petri nets

Abstract: Object-oriented methodologies are increasingly used in software development Despite the proposal of several formally based models, current object-oriented practice is still dominated by informal methodologies, like Booch, OMT, and UML Unfortunately, the lack of dynamic semantics of such methodologies limits the possibility of early analysis of specifications This paper indicates the feasibility of ascribing formal semantics to UML by defining translation rules that automatically map UML specifications to high-level Petri nets This paper illustrates the method through the hurried philosophers problem, that is first specified by using (a subset of) UML, and then mapped onto high-level Petri nets The paper indicates how UML specifications can be verified by discussing properties of the hurried philosophers problem that can be verified on the derived highlevel Petri net

An integrated approach to disassembly planning and demanufacturing operation

Abstract: Industrial demanufacturing is a practice of growing importance due to increasing environmental and economic pressures. However, very little research focuses on it from a system perspective. This paper presents a disassembly planning and demanufacturing scheduling method for an integrated flexible demanufacturing system. Workstation Petri net and Product Petri net are proposed for its hierarchical and modular modeling in order to derive the disassembly path with the maximal end-of-life value. Scheduling Petri net is introduced to schedule the demanufacturing resources. The proposed methodology and algorithms are demonstrated through the disassembly of personal computers in an integrated flexible demanufacturing system.

“What Is a Petri Net?” Informal Answers for the Informed Reader

Abstract: The increasing number of Petri net variants naturally leads to the question whether the term “Petri net” is more than a common name for very different concepts This contribution tries to identify aspects common to all or at least to most Petri nets It concentrates on those features where Petri nets significantly differ from other modeling languages, ie we ask where the use of Petri nets leads to advantages compared to other languages Different techniques that are usually comprised under the header “analysis” are distinguished with respect to the analysis aim Finally, the role of Petri nets in the development of distributed systems is discussed

Modelling the Structure and Behaviour of Petri Net Agents

Abstract: This work proposes a way to model the structure and behaviour of agents in terms of executable coloured Petri net protocols. Structure and behaviour are not all aspects of agent based computing: agents need a world to live in (mostly divided into platforms), they need a general structure (e.g. including a standard interface for communication) and their own special behaviour. Our approach tackles all three parts in terms of Petri nets. This paper skips the topic of agent platforms and handles the agent structure briefly to introduce a key concept of our work: the graphical modelling of the behaviour of autonomous and adaptive agents. A special kind of coloured Petri nets is being used throughout the work: reference nets. Complex agent behaviour is achieved via dynamic composition of simpler sub-protocols, a task that reference nets are especially well suited for. The inherent concurrency of Petri nets is another point that makes it easy to model agents: multiple threads of control are (nearly) automatically implied in Petri nets.

FunState-an internal design representation for codesign

Abstract: In this paper, an internal design model called FunState (functions driven by state machines) is presented that enables the representation of different types of system components and scheduling mechanisms using a mixture of functional programming and state machines. It is shown how properties relevant for scheduling and verification of specification models such as Boolean dataflow, cyclostatic dataflow, synchronous dataflow, marked graphs, and communicating state machines as well as Petri nets can be represented in the FunState model of computation. Examples of methods suited for FunState are described, such as scheduling and verification. They are based on the representation of the model's state transitions in the form of a periodic graph. The feasibility of the novel approach is shown with an asynchronous transfer mode switch example.

Process modeling and analysis of manufacturing supply chain networks using object-oriented Petri nets

Abstract: This paper presents a systematic methodology for modeling and analysis of manufacturing supply chain business processes. The proposed approach first employs Computer Integrated Manufacturing Open System Architecture (CIMOSA) behavior rules to model the business process routing structures of manufacturing supply chain networks. Object-oriented predicate/transition nets (OPTNs) are then developed for the modular modeling and analysis of process models. Based on the structure of OPTNs, a procedure to obtain the system's P -invariants through objects’ P -invariants is suggested. From the P -invariants obtained, system structural properties such as deadlock and overflow can be analyzed. By using Petri net unfolding techniques and by extracting the process model of each object from the entire process model, the sequencing analysis for operations in supply chain processes becomes possible. Several manufacturing supply chain examples are used to illustrate the effectiveness of the proposed method.

Events in security protocols

Abstract: The events of a security protocol and their causal dependency can play an important role in the analysis of security properties. This insight underlies both strand spaces and the inductive method. But neither of these approaches builds up the events of a protocol in a compositional way, so that there is an informal spring from the protocol to its model. By broadening the models to certain kinds of Petri nets, a restricted form of contextual nets, a compositional event-based semantics is given to an economical, but expressive, language for describing security protocols; so the events and dependency of a wide range of protocols are determined once and for all. The net semantics is formally related to a transition semantics, strand spaces and inductive rules, as well as trace languages and event structures, so unifying a range of approaches, as well as providing conditions under which particular, more limited, models are adequate for the analysis of protocols. The net semantics allows the derivation of general properties and proof principles which are demonstrated in establishing an authentication property, following a diagrammatic style of proof.

Rewriting Logic as a Unifying Framework for Petri Nets

Abstract: We propose rewriting logic as a unifying framework for a wide range of Petri 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 Petri nets as a special case. The soundness and completeness results we state relate the commutative process semantics of Petri 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 Petri 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 Petri nets within a single framework, the rewriting semantics can provide a guide for future extensions of Petri 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 Petri 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.