可达性等价于状态方程可满足性的一个petri网子类

本文定义了一个petri网子类： ,满足条件 。本文证明：当目标标识 时,此petri网子类的可达性等价于状态方程 的可满足性。同时,当此petri网子类的可达性等价于状态方程可满足性时,可得出如下两点结论：①对于满足 的每个非平凡的非负整数向量 ,都 ;②对于满足 的每个非平凡的非负整数向量 , 都是 的一个可执行向量。     

A valuation-based analysis of conflict-free Petri nets

We propose a novel valuation-based approach for analyzing conflict-free Petri nets. The basic idea is to associate a natural number, called the valuation, to each marking in the Petri net. If the set of markings of zero valuation is forward closed, then the valuation along any Petri net computation is nonincreasing, and in many cases, has the tendency to move towards zero valuation. Using the valuation-based method, we demonstrate a number of problems for conflict-free Petri nets to be decidable.     

Modular state space exploration for timed petri nets

This paper extends modular state space construction for concurrent systems to cater for timed systems. It identifies different forms of timed state space and presents algorithms for computing them. These include uniprocessor algorithms inspired by conservative and optimistic approaches to discrete event simulation, and also a distributed algorithm. The paper discusses implementation issues and performance results for a simple case study.     

Specification of software pipelining using petri nets

This paper presents a flexible model for software pipelining using the petri nets. Our technique, called the Petri Net Pacemaker (PNP), can create near optimal pipelines with less algorithmic effort than other techniques. The pacemaker is a novel idea which exploits the cyclic behavior of petri nets to model the problem of scheduling operations of a loop body for software pipelining. A way of improving the performance of loops containing predicates is given. The PNP technique also shows how nested loops can be pipelined. A comparison with some of the other techniques is presented. THis work was partially supported by the National Science Foundation under grants CDA-9100788 and CDA-9200371.     

Verification of causal models using petri nets

Many different approaches, mainly based on logical formalisms, have been proposed for modeling causal knowledge and the inferential mechanisms based on this type of knowledge. In this article we present an alternative approach to this problem in which the semantics of a causal model is provided by adopting Petri nets. We show how this scheme of modeling is powerful enough to capture all crucial aspects of the corresponding causal model, without resorting to very complex structures; indeed, the model is obtained using a particular type of deterministic Petri net. Moreover, a complete formalization of the aspects concerning the correctness of the represented causal model is provided in terms of reachability in the Petri net. We believe that this aspect is very important in the knowledge acquisition phase when precise correctness criteria should be defined and respected in the construction of the model. We analyze some of these criteria and we discuss an algorithm (based on a backward simulation of the net) capable of discovering incorrectness by exploiting analysis tools available for Petri nets and the explicit parallelism of the model. © 1992 John Wiley & Sons, Inc.     

Analysis of multi-agent activity using petri nets

This paper presents the use of place/transition petri nets (PNs) for the recognition and evaluation of complex multi-agent activities. The PNs were built automatically from the activity templates that are routinely used by experts to encode domain-specific knowledge. The PNs were built in such a way that they encoded the complex temporal relations between the individual activity actions. We extended the original PN formalism to handle the propagation of evidence using net tokens. The evaluation of the spatial and temporal properties of the actions was carried out using trajectory-based action detectors and probabilistic models of the action durations. The presented approach was evaluated using several examples of real basketball activities. The obtained experimental results suggest that this approach can be used to determine the type of activity that a team has performed as well as the stage at which the activity ended.     

A synthesis technique of general petri nets

The general Petri net (GPN) is useful for modeling flexible manufacturing systems with multiple robots and workstations [15] and for parallel programs [8]. A problem of using reachability analysis for analyzing Petri nets (PN) is the large number of states generated. Most of the existing synthesis techniques do not deal with GPN. Koh et al.[15] invented a synthesis technique for GPN. We propose to improve their achievement by adding the simple Arc-ratio rules to Yaw's knitting technique [37, 38, 39] based on the notion of structure relationship together with new path generations, which mark the most distinct feature compared with other approaches. The synthesis rules and procedures of how to update the temporal matrix and structure synchronic distance are presented. The Arc-ratio rules for GPN are also presented. One can successfully synthesize complicated Petri nets using these rules. An example to synthesize a Petri net in [15] is illustrated. The correctness of each synthesis rule with an appropriate Arc-ratio rule for GPN is proved.     

Modelling automated manufacturing systems using a modification of coloured petri nets

Automated manufacturing systems (AMS) are a class of systems exhibiting concurrency, asynchronicity and distributedness, and can be modelled using Petri nets. The advantage of using Petri nets is that they provide graphical models, with formal methods of analysis. However, graphical representation of Petri net models becomes difficult even for medium-sized systems since such graphs tend to become inconveniently large. Coloured Petri nets (CPN) are a variant which enables a more concise representation with the same modelling power. This paper develops a model for simulation of AMS whose correctness can be formally established, and which can be graphically represented and visually understood. It presents a modelling approach for AMS, based on a modified version of CPN, with enhanced modelling power. The proposed modifications result in highly compact graphical representations, and also render the model dynamic, i.e. capable of changing dynamically to reflect currently selected system parameters. These features make the proposed model ideally suited for discrete event simulation.     

A new methodology for analyzing distributed systems modeled by petri nets

Distributed computing systems can be modeled adequately by Petri nets. The computation of invariants of Petri nets becomes necessary for proving the properties of modeled systems. This paper presents a two-phase, bottom-up approach for invariant computation and analysis of Petri nets. In the first phase, a newly defined subnet, called the RP-subnet, with an invariant is chosen. In the second phase, the selected RP-subnet is analyzed. Our methodology is illustrated with two examples viz., the dining philosophers' problem and the connection-disconnection phase of a transport protocol. We believe that this new method, which is computationally no worse than the existing techniques, would simplify the analysis of many practical distributed systems.     

应用Petri网求解事故树最小割集的方法研究

为简化事故树分析过程中最小割集求解算法的步骤,在构建事故树Petri网模型的基础上,探讨了事故树Petri网模型的性质,给出了事故树的逻辑表达式与事故树Petri网模型的可达死标识之间的关系,进而提出了利用Petri网可达图求解事故树最小割集的算法,以及在给定基本事件发生时,中间事件和顶事件发生与否的判断方法。结合实例,借助开源的Petri网工具PIPE实现了事故树最小割集的求解,表明了该算法的有效性和可行性。     

Verification of problem-based learning systems using modified petri nets

In this paper, we intend to verify a web-based system on problem-based learning (PBL). To consider the design flow of the web-based PBL system, it is essential to avoid the potential hazard introduced by a logically incorrect system design. In order to eliminate the potential hazard, we define a new class of Petri net, namely, an Activity Flow (AF) net, which is suitable to be converted from a UML (Unified Modeling Language) activity diagram. Through the siphon-based deadlock detection of the AF net, we can find whether there is a process hazard in the UML activity diagram or not. This is helpful to implement the PBL system and to ensure the correct activities and the right control flow. In addition, we attempt to enhance the quality of the system verification by using a questionnaire. Thus we can interpret the user’s level of satisfaction with the designed PBL system. These two verification approaches bring us to achieve an adequately positive response to the web-based PBL system.     

基于广义随机Petri网的CIMS多任务可靠性研究

CIMS生产的复杂性要求其可靠性模型可以精确地反映生产过程,由于传统的可靠性建模方法无法兼顾CIMS的时间动态特性,所以针对一个复杂的有多个加工任务的CIMS制造单元,由于其机器加工工件的时间均为指数分布,则采用广义随机Petri网进行多任务可靠性建模,在此基础上基于Petri网行为表达式,将矩母函数思想引入其中,不必生成可达标识图就可通过计算模型的传递函数,进而得到整个系统的多任务可靠度,该可靠性指标可以更直观地反映具有多种加工任务的整个CIMS的运行性能。     

Using transition set sequences to partition behaviors of petri nets

The transition set semantics (Wang and Jiao, LNCS 6128:84–103, 2010) partitions the Petri net behaviors in a canonical way such that behaviors in an equivalence class have the same canonical transition set sequence. This article extends the semantics in two ways: firstly, the semantics is parameterized by the basic relation on the structural transitions to define different variants; secondly, the semantics for the infinite firing sequences of the net is defined. We prove that these extensions still preserve the well-definedness, soundness and completeness of the semantics. Furthermore, we show how to recognize some infinite sequences called back-loops in the view of this new semantics.     

基于颜色Petri网的不确定库存模型性能仿真

供应链中由于信息传递过程中出现的信息膨胀引起牛鞭效应造成各种成本的急剧增长,为使目标函数费用最小,基于颜色Petri网建立了不同需求预测方法及库存策略的CPN模型。在订单数量等变量随机产生以及订货点等因素不确定的情况下,通过实验仿真数据确定了存储、订货及缺货费用与各种不确定变量的关系,从而确定了最优的库存策略。通过对比实验证明了该方法的有效性及正确性。     

Timed petri nets in modeling and analysis of simple schedules for manufacturing cells

It is shown that a large class of flexible manufacturing cells can be modeled using timed Petri nets. Net models of simple schedules (i.e., schedules in which exactly one part enters and one leaves the cell during each cycle) are conflict-free nets. Two complementary approaches to analysis of such models are presented: invariant analysis and throughput analysis. Invariant analysis provides analytic (or symbolic) solutions for the cycle time of a cell analyzing (invariant) subnets of the original net. Throughput analysis performs a series of performance-preserving net reductions to simplify the original model. Several directions for further research are indicated.