An Approach for Minimizing Spurious Errors in Testing ADA Tasking Programs

We propose an approach for detecting deadlocks and race conditions in Ada tasking software. It is based on an extension to Petri net-based techniques, where a concurrent program is modeled as a Petri net and a reachability graph is then derived and analyzed for desired information. In this approach, Predicate-Action subnets representing Ada programming constructs are described, where predicates and actions are attached to transitions. Predicates are those found in decision statements. Actions involve updating the status of the variables that affect the tasking behavior of the program and updating the Read and Write sets of shared variables. The shared variables are those occurring in sections of the program, called concurrency zones, related to the transitions. Modeling of a tasking program is accomplished by using the basic subnets as building blocks in translating only tasking-related statements and connecting them to produce the total Predicate-Action net model augmented with sets of shared variables. An augmented reachability graph is then derived by executing the net model. Deadlocks and race conditions are detected by searching the nodes of this graph. The main advantage offered by this approach is that the Predicate-Action extension of the net leads to pruning infeasible paths in the reachability graph and, thus, reducing the spurious error reports encountered in previous approaches. Also, this approach enables a partial handling of loops in a practical way. Implementation issues are also discussed in the paper

Property-preserving subnet reductions for designing manufacturing systems with shared resources

AbstractThis paper handles two problems in manufacturing system design: resource sharing and system abstraction. In a manufacturing system, resources such as robots, machines, etc. are shared by several processes. When the resources are switched from one process to another, they may need some modifications such as cleaning oil, adding equipments and so on. Previous designing methods assume that the resources have no intermediate modifications. Hence, they need to be extended to handle such kinds of resource-sharing problems. As for abstraction, modeling operations with single places in manufacturing system design is very popular. From the viewpoint of verification, the objective is to verify whether the reduced model has the same desirable properties as the original one. This paper presents three kinds of property-preserving subnet reduction methods. For each reduction method, conditions are presented for ensuring that the properties liveness, boundedness and reversibility are preserved. Applications of these reduction methods to handling the above resource sharing and system abstraction problems are illustrated with an example from the manufacturing system

Stepwise reduction and approximation method for performance analysis of generalized stochastic petri nets

This thesis delves into the performance analysis of generalized stochastic Petri net (GSPN) model by using an approximation method: the Stepwise Reduction and Approximation (SRA) Method. The key point is that we are able to analyze a subnet in isolation by keeping its token flow direction and its sub-throughput equivalent with all the possible tokens entering into the subnet. The thesis first defines various kinds of potentially reducible subnets, subnet selection rules, approximation subnet construction rules, and reduction evaluation rules. Then corresponding to the possible subnets, the approximation method is used stepwisely until the interested measures are found with the global state space reduced. Two GSPN model examples from the literature are analyzed by using the proposed method. The approximation errors are given and discussed. Finally, the conclusions are drawn and future research is discussed

Software development for analysis of stochastic petri nets using transfer functions

This thesis research is an implementation of a closed-form analytical technique for study, evaluation and analysis of Stochastic Petri Nets (SPN). The technique is based on a theorem that an isomorphism exists between an SPN and a Markov Chain. The procedure comprises five main steps: reachability graph generation of the underlying Petri net, transformation of the reachability graph to a state machine Petri net, calculation of transfer functions, computation of equivalent transfer functions via Mason\u27s rule, and computation of performance parameters of the SPN model from the equivalent transfer functions and their derivatives. The software is developed in UNIX using C and applied to various SPN models. Future research includes implementation of Mason\u27s rule for complex cases and symbolic derivation of equivalent transfer functions

Petri net modeling and analysis of an FMS cell

Petri nets have evolved into a powerful tool for the modeling, analysis and design of asynchronous, concurrent systems. This thesis presents the modeling and analysis of a flexible manufacturing system (FMS) cell using Petri nets. In order to improve the productivity of such systems, the building of mathematical models is a crucial step. In this thesis, the theory and application of Petri nets are presented with emphasis on their application to the modeling and analysis of practical automated manufacturing systems. The theory of Petri nets includes their basic notation and properties. In order to illustrate how a Petri net with desirable properties can be modeled, this thesis describes the detailed modeling process for an FMS cell. During the process, top-down refinement, system decomposition, and modular composition ideas are used to achieve the hierarchy and preservation of important system properties. These properties include liveness, boundedness, and reversibility. This thesis also presents two illustrations showing the method adopted to model any manufacturing systems using ordinary Petri nets. The first example deals with a typical resource sharing problem and the second the modeling of Fanuc Machining Center at New Jersey Institute of Technology. Furthermore, this thesis presents the analysis of a timed Petri net for cycle time, system throughput and equipment utilization. The timed (deterministic) Petri net is first converted into an equivalent timed marked graph. Then the standard procedure to find the cycle time for marked graphs is applied. Secondly, stochastic Petri net is analyzed using SPNP software package for obtaining the system throughput and equipment utilization. This thesis is of significance in the sense that it provides industrial engineers and academic researchers with a comprehensive real-life example of applying Petri net theory to modeling and analysis of FMS cells. This will help them develop their own applications

A Petri Net-Based Tool for Detecting Deadlocks and Race Conditions in Concurrent Programs

A static analysis tool for detecting deadlocks and potential race conditions on shared variables in concurrent programs is presented. It is based on Petri Net modeling and reachability analysis, where a concurrent program is modeled as an augmented Petri net and a reachability graph is then derived and analyzed for desired information. Place-Transition subnets representing programming language constructs are described. Transitions in these subnets are augmented with sets of shared variables that occur in sections of the program, called concurrency zones, related to the transitions. The tool consists of four modules. The modeling module employs the augmented subnets as building blocks in translating only the synchronization-related statements of a concurrent program and connects the subnets to yield the total model. The second module produces an augmented reachability graph for the augmented Petri net. The analyzer module searches the augmented reachability graph for deadlocks, race conditions and other useful analysis information requested by the user about the underlying program. The user interface is provided by an X-window based module. Ada is used as a representative of concurrent languages that adopt the rendezvous model of interprocess communication and synchronization. The validation of the tool, its applicability and limitations are also discussed

Petri net approaches for modeling, controlling, and validating flexible manufacturing systems

In this dissertation, we introduce the fundamental ideas and constructs of Petri net models such as ordinary, timed, colored, stochastic, control, and neural, and present some studies that emphasize Petri nets theories and applications as extended research fields that provide suitable platforms in modeling, controlling, validating, and evaluating concurrent systems, information systems, and a versatile dynamic system and manufacturing systems;We then suggest some of extensions that help make Petri nets useful for modeling and analyzing discrete event systems and manufacturing systems models based on the context of a versatile manufacturing system, and applies extended Petri nets models to several manufacturing systems such as an assembly cell, an Automated Palletized Conveyor System, and a tooling machine to show increased modeling power and efficient analysis methods;Finally, Validation methods are presented for these models and results of a performance analysis from a deterministic and stochastic model are used to reorganize and re-evaluate a manufacturing system in order to increase its flexibility

A new approach to the development and maintenance of industrial sequence logic

This thesis is concerned with sequence logic as found in industrial control systems, with the focus being on process and manufacturing control systems. At its core is the assertion that there is a need for a better approach to the development of industrial sequence logic to satisfy the life-cycle requirements, and that many of the ingredients required to deliver such an approach are now available. The needs are discussed by considering the business case for automation and deficiencies with traditional approaches. A set of requirements is then derived for an integrated development environment to address the business needs throughout the control system life-cycle. The strengths and weaknesses of relevant control system technology and standards are reviewed and their bias towards implementation described. Mathematical models, graphical methods and software tools are then assessed with respect to the requirements for an integrated development environment. A solution to the requirements, called Synect is then introduced. Synect combines a methodology using familiar graphical notations with Petri net modelling supported by a set of software tools. Its key features are justified with reference to the requirements. A set of case studies forms the basis of an evaluation against business needs by comparing the Synect methodology with current approaches. The industrial relevance and exploitation are then briefly described. The thesis ends with a review of the key conclusions along with contributions to knowledge and suggestions for further research

Uma abordagem para a modelagem, analise e controle de sistemas de produção utilizando Redes de Petri

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro TecnologicoAs redes de Petri estão sendo atualmente utilizadas em sistemas de manufatura. Neste sentido, o presente trabalho tem como propósito apresentar os diferentes conceitos relativos às redes de Petri e suas várias classes de modelos derivados, os quais podem ser utilizados para modelar sistemas dinâmicos de eventos discretos de qualquer tipo. Esta ferramenta nos permite visualizar com facilidade situações tais como concorrência, sincronização e compartilhamento de recursos, os quais são próprios de um sistema flexível de manufatura (FMS), além do mais, nos permite uma análise tanto qualitativa como quantitativa. Cada um dos modelos derivados tais como RdP estocásticas, RdP colorida, etc. Têm seu próprio caráter específico e campo de aplicação privilegiado