一种基于Petri网的网络服务兼容性分析方法

针对目前基于网络服务业务过程执行语言(BPEL)的网络服务合成方法缺乏网络服务的兼容性分析机制,不能保证基于网络服务技术的业务过程正确执行的问题,建立了一种能从形式化的角度描述网络服务的接口交互情况的基于Petri网的多元工作流组合网模型,提出了一种能更快地获得网络服务可用性结果的网络服务兼容性判断算法.最后,提出了基于该算法的原型系统架构.     

Petri net based scheduling

Timed Petri nets can be used to model and analyse scheduling problems. To support the modelling of scheduling problems, we provide a method to map tasks, resources and constraints onto a timed Petri net. By mapping scheduling problems onto Petri nets, we are able to use standard Petri net theory. In this paper we will show that we can use Petri net based tools and techniques to find conflicting and redundant precedences, upper- and lower-bounds for the makespan, etc. This is illustrated by a Petri net based analysis of the notorious 10×10 problem due to Fisher & Thompson (1963)     

Disassembly sequence plan generation using a branch-and-bound algorithm

This paper presents an approach to generate disassembly sequence plans (DSP) automatically for product recycling and remanufacturing. An algorithm is defined first that generates a geometrically based disassembly precedence matrix (DPM) from a CAD drawing of the product. The DPM is then used to generate a hierarchical disassembly tree (HDT) that represents the feasible DSP. Generation of the HDT, i.e. generation of all feasible DSP, is NP-complete. Thus, to keep the size of the HDT manageable, the branching and bounding processes are controlled using two user-defined variables. The first, w , controls the enumeration of the HDT, while the second, v, controls the bounding procedure in the HDT along with an evaluation function. The evaluation function incorporates tool changes, changes in direction of movement during disassembly along with individual part characteristics (e.g. high-valued parts, parts with hazardous content, etc.). The resulting HDT is called the reduced HDT (RHDT) since it only represents as many (near-) optimum DSP as the size of v. Experimental results demonstrate the applicability and effectiveness of the methodology.     

Disassembly line design with multi-manned workstations: a novel heuristic optimisation approach

As the first and the most time consuming step of product recovery, disassembly is described as the systematic separation of constituent parts from end-of-life products through a series of operations. In this context, designing and balancing disassembly lines are critical in terms of the efficiency of product recovery. Recent research on disassembly line balancing (DLB) has focused on classical stations where only one worker is allocated. However, such a line results in larger space requirement and longer disassembly lead time. In this paper, disassembly line balancing problem (DLBP) with multi-manned stations is introduced to the relevant literature as a solution to overcome these disadvantages. A mixed integer linear programming (MILP) model and two novel framework heuristic algorithms are developed to minimise the number of workers and workstations. MILP model has been applied to a dishwasher disassembly system. The application results indicate the superiority of establishing multi-manned stations over classical disassembly system design with single-worker stations with shorter disassembly lead time (80.9%) and line length (60.2%). Moreover, the proposed heuristics have been compared on newly generated test problems (instances) for DLBP. The results validate that the heuristics provide acceptable solutions in a reasonable amount of time even for large-sized problems.     

A Petri net based design engine for manufacturing systems

Support for the efficient design and operation of complex manufacturing systems requires an integrated modelling, analysis, and control methodology as well as its implementation in a software tool. In this paper the Petri net based design engine TimeNET is presented for this task. Petri nets are able to capture the characteristic features of manufacturing systems in a concise form. A subclass of coloured Petri nets is used, which has been developed especially for the application area of manufacturing. Structure and work plans are modelled separately. Stochastic as well as deterministic and more general distributions are adopted for the firing times of transitions. Fundamental questions about system properties can be answered using qualitative analysis. For an efficient performance and dependability prediction, different evaluation techniques are proposed: direct numerical analysis, approximate analysis, and simulation. Finally, the model can be used to evaluate different control strategies and to control the manufacturing system directly. There is no need to change the modelling methodology, thus avoiding additional effort, for example for model conversion. In the paper this necessary steps are described using an application example.     

Scheduling manufacturing systems with blocking: a Petri net approach

This paper introduces a Petri net-based approach for scheduling manufacturing systems with blocking. The modelling of the job routings and the resource and blocking constraints is carried out with the Petri net formalism due to their capability of representing dynamic, concurrent discrete-event dynamic systems. In addition Petri nets can detect deadlocks typically found in systems with blocking constraints. The scheduling task is performed with an algorithm that combines the classical A* search with an aggressive node-pruning strategy. Tests were conducted on a variety of manufacturing systems that included classical job shop, flexible job shop and flexible manufacturing scheduling problems. The optimisation criterion was makespan. The experiments show that the algorithm performed well in all types of problems both in terms of solution quality and computing times.     

Conflict detection of automated guided vehicles: a Petri net approach

This research project investigates and develops techniques for automatically detecting potential vehicle conflicts in an automated guided vehicle (AGV) system. Three activities are involved: (1) construction of a set of formal definitions of Petri nets for modelling AGV systems; (2) development of procedures for detection of vehicle routeing conflicts; (3) development of a simulation program of the procedure. In this paper the first two activities are discussed in detail, and examples are provided.     

A heuristic algorithm to minimise the control places of a Petri net for the control of shared machines

This paper proposes a design methodology of a controller based on a Petri net for the shared machines of manufacturing systems. A conflict occurs when several manufacturing systems require the same shared machines at the same time. In this case, we have two issues; the scheduling of jobs on shared machines and the construction of a control procedure for scheduling. The scheduling of production on machines has been extensively studied over the past years by researchers. In this paper, our concern is not the scheduling problem but the construction of a control procedure for the production schedule. We propose a design of a Petri net based controller for the shared machines of manufacturing systems such that the number of control places in the Petri net is minimised. The experimental results show that the proposed algorithm performs better than an upper bound in terms of optimality. Also, the proposed algorithm is computationally more efficient than the optimal algorithm. Finally, we present the application of the proposed algorithm to a realistic batch process system shown in the literature.     

A Petri net approach to behavioural simulation of design artefacts with application to mechatronic design

A Petri net-based design inference network (PNDN) architecture is presented in this paper. The network models the logical behaviour of any design artefact developed by designers at the conceptual design level by representing the subfunctions and their inter-relationships to perform a required overall function. The theoretical framework in developing the PNDN is based on the improved theory of Petri nets and hybrid automata. The theoretical PNDN architecture was implemented in a C++ based software called the design network simulator (DNS). The logical behaviour of a design artefact is modelled through the token flow within the PNDN. The token flow model is developed both for deterministic and nondeterministic PNDN, which involves uncertainties. In this paper we present the mathematical formalism of the deterministic token flow through the PNDN. We also provide a conceptual design example in order to explain the application of our theoretical architecture for structuring the PNDN.     

医疗信息系统工作流的Petri网建模与化简分析

应用 Petri网建模与工作流技术,构建了基于医疗信息整合(IHE)规范的医疗信息系统工作流的Petri网模型,并对一个医疗信息系统工作流实例,给出了基于Petri网化简分析方法的模型化简与性质验证,表明该模型能够对医疗信息工作流进行有效的分析和验证,从而为医疗信息系统集成设计及其工作流分析提供了理论基础.     

A coloured Petri net-based hybrid heuristic search approach to simultaneous scheduling of machines and automated guided vehicles

To achieve a significant improvement in the overall performance of a flexible manufacturing system, the scheduling process must consider the interdependencies that exist between the machining and transport systems. However, most works have addressed the scheduling problem as two independent decision making problems, assuming sufficient capacity in the transport system. In this paper, we study the simultaneous scheduling (SS) problem of machines and automated guided vehicles using a timed coloured Petri net (TCPN) approach under two performance objectives; makespan and exit time of the last job. The modelling approach allows the evaluation of all the feasible vehicle assignments as opposed to the traditional dispatching rules and demonstrates the benefits of vehicle-controlled assignments over machine-controlled for certain production scenarios. In contrast with the hierarchical decomposition technique of existing approaches, TCPN is capable of describing the dynamics and evaluating the performance of the SS problem in a single model. Based on TCPN modelling, SS is performed using a hybrid heuristic search algorithm to find optimal or near-optimal schedules by searching through the reachability graph of the TCPN with heuristic functions. Large-sized instances are solved in relatively short computation times, which were a priori unsolvable with conventional search algorithms. The algorithm’s performance is evaluated on a benchmark of 82 test problems. Experimental results indicate that the proposed algorithm performs better than the conventional ones and compares favourably with other approaches.     

Celeritas: a coloured Petri net approach to simulation and control of flexible manufacturing systems

In many areas of computerization today, the capabilities of hardware systems far exceed the sophistication of software systems needed for optimum control. This research is an attempt to advance software control capabilities of flexible manufacturing systems (FMSs). To this end, an FMS controller architecture, called Celeritas, has been designed and a software system conforming to this architecture has been designed and implemented. Celeritas is a generic, data-configurable FMS controller designed using the coloured Petri nets (CP-nets) modelling paradigm augmented with decision support software to provide both FMS simulation and control. Formalisms of the CP-net paradigm provide straightforward representation of both the inherent concurrency and resource conflicts present in such a complex system. Augmentations provide user-defined routines for real-time interfaces to this information which is utilized to provide resource arbitration services among jobs competing for scarce resources and overall job scheduling.     

基于Petri网的可信连接架构的安全属性分析

为确保可信连接架构(TCA)自身的安全可靠,研究了其安全属性量化问题,分析了其双向用户身份认证和平台认证过程中存在的安全威胁.利用随机Petri网对带有攻击行为的TCA可信网络连接过程进行了建模,该模型用于描述攻击行为和TCA的双向认证过程.以该模型为基础构造了马尔科夫链,通过计算马尔科夫模型的稳定状态概率对TCA的稳定状态机密性和完整性等安全属性进行定量分析.最后给出了一个具体数值评估结果的实例.此研究给出的方法有理论和实用意义.     

Ignorance-aware safety and reliability analysis: A heuristic approach

In the current study, we aim to solve a group decision-making problem on the basis of expert judgment with consideration of both global and local ignorance in system safety assessment. When data are acquired from various sources, especially subjective ones, the estimation of the data's precise value is challenging. In such a case, the basic belief assignment (bba) function is utilized to cope with the decision-making procedure on the basis of Dempster-Shafer theory (DST). DST, as an effective tool for manipulating inaccurate values, stills is not adequate to obtain the optimum values under the consideration of global and local subjective ignorance. To address the aforementioned subjects in this study, an innovative heuristic approach using a multiobjective programming model is introduced to derive the optimal values (bba) in the system safety assessment. An illustrative example is provided in detail to show the applicability and feasibility of the introduced heuristic approach.     

Hybrid Petri net and digraph approach for deadlock prevention in automated manufacturing systems

This paper proposes a hybrid approach to deadlock prevention in automated manufacturing systems that combines Petri nets (PNs) and digraphs, so taking advantage of the strong points of both techniques. The approach uses digraphs to make the detection of deadlock conditions easier and then translates the obtained information in empty siphons of the PN modelling the same system. The proposed methodology allows the implementation of new PN‐based deadlock prevention control policies. A case study and the simulation results show the benefits of the new control strategies.     

A heuristic approach on the facility layout problem based on game theory

Facility layout problems are related to the location of all facilities in a plant. Numerous research works related to facility layout have been published. The applicability of these various existing models may be limited by the fact that they all ignore competitive reactions to one's actions. In addition to external competitors, some internal problems of system such as material handling system design affect layout designs. For considering these effects, some researchers have investigated multi-objective approaches that in most cases lead to the optimisation of a weighted sum of score functions. The poor practicability of such an approach is due to the difficulty of normalising these functions and quantifying the weights. To the extent that competitors do react to a firm's actions and also the facility layout problem considers several conflicting objectives by distinct decision makers in the firm, the existing models may be oversimplifications of reality. In this paper, we modelled such a facility layout problem with conflicting objectives under a duopoly Bertrand competition as a game and solved it with a proposed simulated annealing meta-heuristic. Results obtained from solving some numerical examples confirm the effectiveness of the proposed model for the layout design.     

Scheduling of flexible manufacturing systems based on Petri nets and hybrid heuristic search

This paper proposes and evaluates a hybrid search strategy and its application to flexible manufacturing system (FMS) scheduling in a Petri net framework. Petri nets can concisely model multiple lot sizes for each job, the strict precedence constraint, multiple kinds of resources, and concurrent activities. To cope with the complexities for FMS scheduling, this paper presents a hybrid heuristic search strategy, which combines the heuristic A* strategy with the DF strategy based on the execution of the Petri nets. The search scheme can invoke quicker termination conditions, and the quality of the search result is controllable. To demonstrate this, the scheduling results are derived and evaluated through a simple FMS with multiple lot sizes for each job. The algorithm is also applied to a set of randomly generated more complex FMSs with such characteristics as limited buffer sizes, multiple resources, and alternative routings.     

Two FMS scheduling methods based on Petri nets: A global and a local approach

We are interested in the Flexible Manufacturing System (FMS) scheduling problem. Different methods have been explored to solve this problem and to master its combinatorial complexity, which is NP-hard in the general case. In this paper we will give two different scheduling methods based on Petri nets. The first one tends to solve the general scheduling problem (acyclic schedule) using the Constraint Programming method to avoid exhaustive search. The second method is a dedicated cyclic scheduling method. The aim is not to compare the methods' performances (computation time, results' quality) because they do not solve exactly the same problem, but to compare their application domains in terms of parts number.     

Machine loading problem of FMS: A fuzzy-based heuristic approach

The art and science of simulating complex manufacturing systems is rapidly changing. A great deal of attention is being devoted to the possibilities of bringing artificial intelligence (AI) and expert systems (ES) technology into simulation methodology. Such systems will hopefully allow models to be quickly developed, validated and run with as much of the necessary expertise as possible built into the software. This paper addresses: (a) the motivation and need for developing such systems, (b) the nature of such systems, (c) the potential benefits of this technology over existing approaches and (d) the current state-of-the-art as it applies to simulation.