A Petri Net Approach to Verify and Debug Simulation Models

Verification and Simulation share many issues, one is that simulation models require validation and verification. In the context of simulation, verification is understood as the task to ensure that an executable simulation model matches its conceptual counterpart while validation is the task to ensure that a simulation model represents the system under study well enough with respect to the goals of the simulation study. Both, validation and verification, are treated in the literature at a rather high level and seem to be more an art than engineering. This paper considers discrete event simulation of stochastic models that are formulated in a process-oriented language. The ProC/B paradigm is used as a particular example of a class of simulation languages which follow the common process interaction approach and show common concepts used in performance modeling, namely a) layered systems of virtual machines that contain resources and provide services and b) concurrent processes that interact by message passing and shared memory. We describe how Petri net analysis techniques help to verify and debug a large and detailed simulation model of airport logistics. We automatically derive a Petri net that models the control flow of a Proc/B model and we make use of invariant analysis and modelchecking to shed light on the allocation of resources, constraints among entities and causes for deadlocks

ARCHITECTURE-BASED RELIABILITY ANALYSIS OF WEB SERVICES

In a Service Oriented Architecture (SOA), the hierarchical complexity of Web Services (WS) and their interactions with the underlying Application Server (AS) create new challenges in providing a realistic estimate of WS performance and reliability. The current approaches often treat the entire WS environment as a black-box. Thus, the sensitivity of the overall reliability and performance to the behavior of the underlying WS architectures and AS components are not well-understood. In other words, the current research on the architecture-based analysis of WSs is limited. This dissertation presents a novel methodology for modeling the reliability and performance of web services. WSs are treated as atomic entities but the AS is broken down into layers. More specifically, interactions of WSs with the underlying layers of an AS are investigated. One important feature of the research is investigating the impact of dynamic parameters that exist at the layers, such as configuration parameters. These parameters may have negative impact on WSs performance if they are not configured properly. WSs are developed in house and the AS considered is JBoss AS. An experimental environment is setup so that controlled service requests can be generated and important performance metrics can be recorded under various configurations of the AS. On the other hand, a simulation model is developed from the source code and run-time behavior of the existing WS and AS implementations. The model mimics the logical behavior of the WSs based on their communication with the AS layers. The simulation results are compared to the experimental results to ensure the correctness of the model. The architecture of the simulation model, which is based on Stochastic Petri Nets (SPN), is modularized in accordance to the layers and their interactions. As the web services are often executed in a complex and distributed environment, the modularized approach enables a user or a designer to observe and investigate the performance of the entire system under various conditions. In contrast, most approaches to WSs analyses are monolithic in that the entire system is treated as a closed box. The results show that 1) the simulation model can be a viable tool for measuring the performance and reliability of WSs under different loads and conditions that may be of great interest to WS designers and the professionals involved; 2) Configuration parameters have big impacts on the overall performance; 3) The simulation model can be tuned to account for various speeds in terms of communication, hardware, and software; 4) As the simulation model is modularized, it may be used as a foundation for aggregating the modules (layers), nullifying modules, or the model can be enhanced to include other aspects of the WS architecture such as network characteristics and the hardware/operating system on which the AS and WSs execute; and 5) The simulation model is beneficial to predict the performance of web services for those cases that are difficult to replicate in a field study

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

Safety-oriented Testing for High-speed Rail Onboard Equipment Using Petri Nets

With its ability to operate at high speeds and capacity, high-speed rail offers a fast, dependable, and ecofriendly urban transportation option. Safety-critical systems such as high-speed rail signaling systems must be tested regularly to assess compliance with specifications and ensure reliable performance. Given that the onboard equipment is the core component of the signaling system, conducting safety testing on this equipment is of utmost importance. Current methods of analyzing test requirements mainly rely on human interpretation of specifications. However, the official technical specifications usually only outline standard operational scenarios, which could result in an inefficient and unclear safety analysis. This paper focuses on safety-oriented testing for onboard equipment. In particular, we propose a Petri net based approach to generate test cases for diverse operational scenarios. This approach improves both the efficiency and reliability of the testing process while ensuring compliance with safety requirements

Model-based engineering of animated interactive systems for the interactive television environment

Les interfaces graphiques étaient la plupart du temps statiques, et représentaient une succession d'états logiciels les uns après les autres. Cependant, les transitions animées entre ces états statiques font partie intégrante des interfaces utilisateurs modernes, et leurs processus de design et d'implémentations constituent un défi pour les designers et les développeurs. Cette thèse propose un processus de conception de systèmes interactifs centré sur les animations, ainsi qu'une architecture pour la définition et l'implémentation d'animations au sein des interfaces graphiques. L'architecture met en avant une approche à deux niveaux pour définir une vue haut niveau d'une animation (avec un intérêt particulier pour les objets animés, leurs propriétés à être animé et la composition d'animations) ainsi qu'une vue bas niveau traitant des aspects détaillés des animations tels que les timings et les optimisations. Concernant les spécifications formelles de ces deux niveaux, nous utilisons une approche qui facilite les réseaux de Petri orientés objets pour la conception, l'implémentation et la validation d'interfaces utilisateurs animées en fournissant une description complète et non-ambiguë de l'ensemble de l'interface utilisateur, y compris les animations. Enfin, nous décrivons la mise en pratique du processus présenté, illustré par un cas d'étude d'un prototype haute-fidélité d'une interface utilisateur, pour le domaine de la télévision interactive. Ce processus conduira à une spécification formelle et détaillée du système interactif, et incluera des animations utilisant des réseaux de Petri orientés objet (conçus avec l'outil PetShop CASE).Graphical User Interfaces used to be mostly static, representing one software state after the other. However, animated transitions between these static states are an integral part in modern user interfaces and processes for both their design and implementation remain a challenge for designers and developers. This thesis proposes a process for designing interactive systems focusing on animations, along with an architecture for the definition and implementation of animation in user interfaces. The architecture proposes a two levels approach for defining a high-level view of an animation (focusing on animated objects, their properties to be animated and on the composition of animations) and a low-level one dealing with detailed aspects of animations such as timing and optimization. For the formal specification of these two levels, we are using an approach facilitating object-oriented Petri nets to support the design, implementation and validation of animated user interfaces by providing a complete and unambiguous description of the entire user interface including animations. Finally, we describe the application of the presented process exemplified by a case study for a high-fidelity prototype of a user interface for the interactive Television domain. This process will lead to a detailed formal specification of the interactive system, including animations using object-oriented Petri nets (designed with the PetShop CASE tool)