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.     

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.     

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 new approach to verify rule-based systems using petri nets

In the past several years, various graphical techniques were proposed to analyze various types of structural errors, including inconsistency (conflict rules), incompleteness (missing rules), redundancy (redundant rules), and circularity (circular depending rules), in rule-based systems in which rules can be represented in propositional logic. In this paper, we present a special reachability graph technique based on ω-nets (a special type of low-level petri nets) to detect all of the above types of structural errors. Our new technique is simple, efficient, and can be easily automated. We highlight the unique features of this new approach and demonstrate its application through two examples.     

Animation modeling with petri nets

This paper introduces the use of Petri Nets as a modeling and analysis tool for animation environments. Firstly, the original formulation for Petri Nets is applied in two animation situations, one modeled as a state machine and another exploring interdependent transitions. Increasing the complexity level, some modeling extensions are discussed and more sophisticated animation examples are studied.     

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.     

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。     

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.     

An approach towards the verification of expert systems using numerical petri nets

A major difficulty that occurs in the construction of large production rule-based expert systems is maintaining the correctness, consistency, and completeness of the knowledge base. A method of transforming the production rules into a numerical petri nets (NPNs) model is proposed. These NPNs are high level nets that are necessary to effectively model production rules. the net model is then analysed by using a computer-aided tool to perform reachability analysis. an algorithm is given to generate the reachability set of the nets. This allows the verification of the correctness, consistency, and completeness of the knowledge base. Examples showing the use of this approach are given.     

Verification of bounded Petri nets using integer programming

Model checking based on the causal partial order semantics of Petri nets is an approach widely applied to cope with the state space explosion problem. One of the ways to exploit such a semantics is to consider (finite prefixes of) net unfoldings—themselves a class of acyclic Petri nets—which contain enough information, albeit implicit, to reason about the reachable markings of the original Petri nets. In [19], a verification technique for net unfoldings was proposed, in which deadlock detection was reduced to a mixed integer linear programming problem. In this paper, we present a further development of this approach. The essence of the proposed modifications is to transfer the information about causality and conflicts between the events involved in an unfolding, into a relationship between the corresponding integer variables in the system of linear constraints. Moreover, we present some problem-specific optimisation rules, reducing the search space. To solve other verification problems, such as mutual exclusion or marking reachability and coverability, we adopt Contejean and Devie's algorithm for solving systems of linear constraints over the natural numbers domain and refine it, by taking advantage of the specific properties of systems of linear constraints to be solved. Another contribution of this paper is a method of re-formulating some problems specified in terms of Petri nets as problems defined for their unfoldings. Using this method, we obtain a memory efficient translation of a deadlock detection problem for a safe Petri net into an LP problem. We also propose an on-the-fly deadlock detection method. Experimental results demonstrate that the resulting algorithms can achieve significant speedups.

Mapping timed cause-effect structures into timed petri nets

Conclusion The problem of inverse mapping of Petri nets into CES remains an interesting open question. Raczunas [5] claims that it is not for every PN that a strictly equivalent CES exists. He accordingly proposes weak equivalence of this mapping. Kotov [6] defines a topologically structured subclass of PN—regular PN. The subclass of regular PN has the same cardinality as the class of all PN in the sense of behavioral equivalence. It is therefore relevant to compare the class of regular PN with CES. The study was partially financed by the Russian Foundation for Basic Research, grant No. 93-012-986. Translated from Kibernetika i Sistemnyi Analiz, No. 2, pp. 44–54, March–April, 1997.     

Fault tolerant control design via hybrid petri nets

This paper proposes a novel fault tolerant control (FTC) scheme for hybrid systems modeled by hybrid Petri nets (HPNs). The HPNs model consists of discrete and continuous PNs. The faults are represented by unobservable discrete transitions or the normal observable discrete transitions with abnormal firing time in discrete PNs. First, an observer‐based fault diagnosis method is proposed to estimate the marking in discrete places with unknown initial marking and diagnose the faulty behavior simultaneously. Then, an adaptive fault tolerant controller is designed to maintain the general mutual exclusion constraints (GMEC) of discrete PNs, and a scheme that adjusts firing speeds of continuous transitions is provided to maintain the optimality of continuous PNs. Finally, an example of an intelligent transportation system consisting of automated vehicles on a bridge is included to demonstrate the effectiveness of our developed techniques. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society     

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.