基于平行Petri网的制造系统调度与控制一体化方法

为了消除制造系统调度层与控制层之间的隔阂,实现对生产事件快速灵活响应,本文提出了一种调度与控制一体化的方法.首先,定义了一种新型Petri网模型,即平行Petri网,从而集成地描述了传感器、执行器、任务和资源信息,构建制造系统的信息物理系统模型;其次,提出了一种从平行Petri网到赋时Petri网的抽象简化方法,大规模压缩优化调度所需搜索的状态空间;再次,定义了策略Petri网以描述最优调度策略.最后,给出了平行Petri网与策略Petri网同步执行算法,使得平行Petri网与物理系统同步执行.     

Parallel program design using high-level Petri nets

Petri nets are proposed as a general-purpose design and modelling tool for parallel programs. The advantages of Petri nets for this purpose are discussed, and a solution to the Dining Philosophers problem is developed using simple Place-Transition nets. The limitations of Place-Transition nets are described, and the Dining Philosophers problem is used to illustrate how Coloured Petri nets can overcome these limitations. A more complex example of a Coloured Petri net is then given, and it is shown how a collection of processes in the Occam programming language can be developed directly from the properties of the net. Another Petri net model of a simple process farm is given, and a solution is developed in Parallel C: this further highlights the suitability of Petri nets as a design tool for parallel programs.     

Compositional Petri Net Approach to the Development of Concurrent and Distributed Systems

In the paper, a formal model based on Petri nets is proposed in the context of a compositional approach to the development and analysis of complex concurrent and distributed systems. Mutlilabels of Petri nets are introduced allowing labeling a transition not only with a single symbol, but also with a multiset of symbols. Operations on multilabeled Petri nets—parallel composition and restriction—are defined. A definition of a Petri net entity is given based on the notion of multilabels. A Petri net entity is a Petri net with a set of multilabels, where each multilabel is regarded as an access point of the entity. The operation of entity composition is introduced. Equivalence of entities is defined based on bisimulation equivalence of Petri nets. It is shown that the equivalence relation is congruent with respect to entity composition. It is also demonstrated that the composition operation is commutative and associative.     

基于工作流网的实时协同系统模拟技术

基于Petri网和工作流的概念，提出一种实时协同系统的形式化模拟与分析技术——逻辑工作流网，逻辑工作流网是抑制弧Petri网和高级Petri网的抽象和扩展，其变迁的输入／输出受逻辑表达式的约束，它与一般工作流网相比，能够在一定程度上缓解状态空间爆炸问题，且便于系统设计人员掌握和使用，该文分析了逻辑工作流网的若干性质及组合网的性质继承问题，并以网上企业销售系统为例，说明逻辑工作流网在实时协同系统模拟分析中的应用。     

模糊Petri网在带权不精确知识表示和推理中的应用研究

Petri网是一种适合于描述异步并发事件的计算机系统模型 ,可以有效地对并行和并发系统进行形式化验证和行为分析 .以模糊 Petri网的基本定义为基础 ,讨论了带权模糊知识的模糊产生式系统表示法 ,建立了这种表示法与模糊 Petri网之间的映射关系和转换算法 ;在对模糊 Petri网进一步扩充的基础上 ,解决了与知识的模糊Petri网表示相关的几个问题 ;最后给出了模糊 Petri网中不确定性的计算方法和相应的不精确推理算法     

双总线结构工业控制计算机网性能指标评估

本文对双总线结构工业控制计算机网给出了其Ｐｅｔｒｉ网和高级Ｐｅｔｒｉ网的建模及性能指标评估方法。文中考虑了信包缓冲区容量有限、信包最大允许服务时间有限、不同的站点优先级和系统总线故障率等因素影响下的网络性能指标评估问题。克服了以往对网络性能评估的某些局限。本文讨论了带计数禁止弧的高级随机Ｐｅｔｒｉ网（ＨＤＳＰＮ）的特性，并对给出的ＤＳＰＮ模型进行了仿真计算，对影响网络性能的系统指标进行了讨论。     

基于Petri网的业务流程成本分析方法

Petri网是一个功能强大的建模工具,已广泛应用于业务流程的建模与分析,但是原型Petri网对业务流程的成本分析却无能为力.首先介绍原型Petri网的定义,然后针对实际业务流程建模中成本预算分析的需要,对原型Petri网扩展价格因素,定义了价格Petri网及其变迁触发规则,而后定义了计价状态空间的概念,并给出计价状态可达空间的构造算法,最后通过一个例子说明价格Petri网可以有效地对业务流程进行成本分析.     

Real-time software specification and validation with Transnet

The paper presents the executable specification method for real-time (embedded) systems Transnet. The method is based on an extension to Petri nets. A specification is developed by a problem decomposition into a set of parallel processes. Each process is defined by an extended Petri net with functions assigned to transitions, and conditions and time constants assigned to arcs. It is shown that Transnet matches with the characteristics of the intended class of applications. The available specification languages and the internal representation of data which describe the functional as well as nonfunctional requirements are outlined. The advantages of the Petri net-based representation and the possibilities of automatic net analysis and early validation are discussed.     

模糊时间Petri网及其时间推理方法

Petri网是一种用网状图形表示系统模型的方法,它能够从组织结构、控制和管理的角度,精确描述系统中事件(变迁)之间的依赖(顺序)和不依赖(并发)关系。但传统的Petri网理论其不足之处在于:它的分析方法主要是可达树分析法和线性代数描述法。可达树分析法是针对某一个初始标识的,一个新的初始标识就意味着需要重新构造可达状态图;当系统存在较多     

Performance analysis of stochastic timed Petri nets using linearprogramming approach

Stochastic timed Petri nets are a useful tool in the performance analysis of concurrent systems such as parallel computers, communication networks and flexible manufacturing systems. In general, performance measures of stochastic timed Petri nets are difficult to obtain for practical problems due to their sizes. In this paper, we provide a method to efficiently compute upper and lower bounds for the throughputs and mean token numbers for a large class of stochastic timed Petri nets. Our approach is based on uniformization technique and linear programming     

基于知识Petri网和归结规则的推理方法

本文提出了一种基于知识Petri网和归结规则的推理方法.通过知识Petri网描述命题逻辑知识库,将归结规则映射到知识Petri网上,根据库所和变迁的连接关系,定义了知识Petri网中的归结结构.利用归结结构,给出了基于知识Petri网的归结推理算法和扩展知识库的推理算法,并利用Wumpus实例验证了推理算法.该推理方法是可靠且完备的,能够利用知识Petri网的网络结构降低计算复杂性.     

Statechartable Petri nets

Petri nets and statecharts can model concurrent systems in a succinct way. While translations from statecharts to Petri nets exist, a well-defined translation from Petri nets to statecharts is lacking. Such a translation should map an input net to a corresponding statechart, having a structure and behaviour similar to that of the input net. Since statecharts can only model a restricted form of concurrency, not every Petri net has a corresponding statechart. We identify a class of Petri nets, called statechartable nets, that can be translated to corresponding statecharts. Statechartable Petri nets are structurally defined using the novel notion of an area. We also define a structural translation that maps each statechartable Petri net to a corresponding statechart. The translation is proven sound and complete for statechartable Petri nets.     

Fuzzy Petri nets with neural networks to model products qualityfrom a CNC-milling machining centre

This paper presents a Petri net approach for the modeling of a CNC-milling machining centre. Next, by utilizing fuzzy logic with Petri nets (fuzzy Petri nets), a technique based on 9 fuzzy rules is developed. This paper demonstrates how fuzzy input variables, fuzzy marking, fuzzy firing sequences, and a global output variable should be defined for use with fuzzy Petri nets. The technique employs two fuzzy input variables (spindle speed and feed rate), throughout the milling operation in order to determine surface roughness. Additionally, a fuzzy Petri net is used with an artificial neural network for the modeling and control of surface roughness. Experimental results illustrate that the technique developed can be of benefit when the cutting tool has suffered damage throughout the milling operation. It also shows how the technique can react when the quality is high, medium, or low. The surface roughness represents the quality specification of products from the CNC-milling machining centre     

Net structure and control logic synthesis of controlled Petri nets

Control logic synthesis of discrete-event systems is considered in the setting of controlled Petri nets. The problem is to find a control policy that restricts the behavior of a controlled Petri net so that a collection of forbidden state conditions is satisfied. S-decreases are introduced as a tool for the control synthesis. The S-decreases are weight vectors defined on the places of a net such that the weighted sum of tokens in the net never increases with any transition firing. On the basis of S-decreases, the authors propose an efficient method for the synthesis of the maximally permissive state feedback control polity for a class of controlled Petri nets whose uncontrolled subnets are forward and backward conflict-free nets. This method upgrades all integer linear programming-based methods for which one only requires to solve the much simpler linear programming problems to determine maximally permissive controls     

An interactive tool for design,simulation, verification,and synthesis of protocols

We have developed a user-friendly CAD graphical tool for the design, verification, simulation, and synthesis of protocols based on an interactive tool for Petri net and state diagram designs. Special features of this tool are: the capability of modeling both control and data flows, reduction and analysis, simulation of network behavior and performance, coding (parametrized protocols and automatic implementation), synthesis (two party protocol and ordinary Petri nets), animation and flexible design. Since it is Petri-net based, it allows simulation during all design phases and has extensive applications such as parallel debugging and simulation, expert systems, etc. Future enhancements of this tool are also discussed.     

Development of context-aware workflow systems based on Petri Net Markup Language

The Petri Net Markup Language (PNML) is originally an XML-based interchange format for Petri nets. Individual companies may specify their process models in Petri nets and exchange the Petri nets with other companies in PNML. This paper aims to demonstrate the capabilities of PNML in the development of applications instead of an industrial interchange format only. In this paper, we apply PNML to develop context-aware workflow systems. In existing literature, different methodologies for the design of context-aware systems have been proposed. However, workflow models have not been considered in these methodologies. Our interests in this paper are to propose a methodology to automatically generate context-aware action lists for users and effectively control resource allocation based on the state of the workflow systems. To achieve these objectives, we first propose Petri net models to describe the workflows. Next, we propose models to capture resource activities. Finally, the interactions between workflows and resources are combined to obtain a model for the whole processes. Based on the combined model, we propose architecture to automatically generate context-aware graphical user interface to guide the users and control resource allocation in workflow systems. We demonstrate our design methodology using a health care example.     

Petri网系统的功能划分及其并行算法

针对Petri网系统的并行控制与执行,提出Petri网系统的功能划分及其并行算法。采用库所不变量技术对Petri网系统进行功能划分,给出非负库所不变量的功能划分算法。对进程内和进程间的并行性进行分析,给出消息传递环境下Petri网并行算法及应用示例。实验结果表明,该算法能较好地体现Petri网系统的实际运行过程,是实现Petri网系统并行控制和运行的有效方法。     

Overlapping decompositions and expansions of Petri nets

Overlapping decompositions and expansions are considered to design decentralized controllers for discrete-event systems (DESs) modeled by Petri nets. The inclusion principle for Petri nets is first defined. It is shown that properties like boundedness, reversibility, and liveness (with a mild additional condition) carry over from the including net to the included net. Moreover, a new property called obstruction, is introduced for the including net, and it is shown that if obstruction does not occur in the including net, then deadlock does not occur in the included net. An expansion procedure, which guarantees inclusion for an overlappingly decomposed Petri net, is then introduced     

Two theoretical and practical aspects of knitting technique:invariants and a new class of Petri net

We present two aspects of knitting technique, the structural properties (especially the P- and T-invariants), and the synchronized choice net (a new class of Petri net), that are of both theoretical importance and practical uses to the verification of structural correctness of a Petri net or to detect the structural problem of a Petri net. This work first proves that the ordinary Petri nets synthesized with knitting technique are structurally bounded, consistent, conservative and safe (when each home place holds one token) using the well-known linear algebra approach. It also provides a procedure for finding P- and T-invariants for Petri net synthesized using the knitting technique. We present examples for P-invariants and show that we can synthesize Petri nets more general than the "asymmetric-choice nets". The algorithm for finding P-invariants of ordinary Petri nets is extended to find the P-invariants for a general Petri net synthesized with knitting technique and the arc-ratio rules. We present a new class of Petri nets, called synchronized choice nets, which are the largest set of Petri nets that can be covered by both T-components and P-components. An algorithm is proposed to find its T-components and the P-components, respectively. The complexity of this algorithm is also presented. The theory of synchronized choice nets has the potential to simplify that for free choice nets.