Structuring and composability issues in Petri nets modeling

Along Petri nets' history, numerous approaches have been proposed that try to manage model size through the introduction of structuring mechanisms allowing hierarchical representations and model composability. This paper proposes a classification system for Petri nets' structuring mechanisms and discusses each one of them. These include node fusion, node vectors, high-level nets, and object-oriented inspired Petri nets extensions, among others. One running example is used emphasizing the application of the presented mechanisms to specific areas, namely to automation systems modeling, and software engineering, where object-oriented modeling plays a major role

On the use of programming languages for textual specification of Petri Net Models

O presente artigo revê e aprofunda o artigo intitulado Towards a Human-Friendly Textual Language for Petri Nets, apresentado no Workshop on Petri Net Standards 2007.As a general interchange format for Petri net models, the Petri Net Markup Language (PNML) allows the specification of Petri net models for all Petri net classes. Those models are typically generated by graphical editors for each Petri net type. Yet, there is no general way to specify Petri net models in a human-friendly textual notation. Instead of proposing a standard for such textual notation, this paper proposes the use of popular general purpose programming languages for the creation and modification of net models defined using PNML. To that end, the paper presents a model for the concepts, and the respective inter- relations, that should be available to define Petri net models in a compact textual format. After, it presents a general framework to specify model composition, using node fusion, for any Petri net class. The framework allows the specification of node fusions and node refinements based on the specification of fusions for each node and net label. The labels’ fusions are defined through the implementation of an abstract data type for the respective Petri net type definition. This allows a general support for model structuring, where several well-known graphical conveniences, e.g. node references and synchronous channels, can be supported and seen as particular cases

Scenario-based modeling in industrial information systems

This manuscript addresses the creation of scenario-based models to reason about the behavior of existing industrial information systems. In our approach the system behavior is modeled in two steps that gradually introduce detail and formality. This manuscript addresses the first step, where text-based descriptions, in the form of structured rules, are used to specify how the system is or should be regulated. Those rules can be used to create behavioral snapshots, which are collections of scenario-based descriptions that represent different instances of the system behavior. Snapshots are specified in an intuitive and graphical notation that considers the elements from the problem domain and permit designers to discuss and validate the externally observable behavior, together with the domain experts. In the second step (not fully covered in this manuscript), the system behavior is formalized with an executable model. This formal model, which in our approach is specified using the Colored Petri Net (CP-nets) language, allows the system internal behavior to be animated, simulated, and optimized. The insights gained by experimenting with the formal model can be subsequently used for reengineering the existing system

Attack-Surface Metrics, OSSTMM and Common Criteria Based Approach to “Composable Security” in Complex Systems

In recent studies on Complex Systems and Systems-of-Systems theory, a huge effort has been put to cope with behavioral problems, i.e. the possibility of controlling a desired overall or end-to-end behavior by acting on the individual elements that constitute the system itself. This problem is particularly important in the “SMART” environments, where the huge number of devices, their significant computational capabilities as well as their tight interconnection produce a complex architecture for which it is difficult to predict (and control) a desired behavior; furthermore, if the scenario is allowed to dynamically evolve through the modification of both topology and subsystems composition, then the control problem becomes a real challenge. In this perspective, the purpose of this paper is to cope with a specific class of control problems in complex systems, the “composability of security functionalities”, recently introduced by the European Funded research through the pSHIELD and nSHIELD projects (ARTEMIS-JU programme). In a nutshell, the objective of this research is to define a control framework that, given a target security level for a specific application scenario, is able to i) discover the system elements, ii) quantify the security level of each element as well as its contribution to the security of the overall system, and iii) compute the control action to be applied on such elements to reach the security target. The main innovations proposed by the authors are: i) the definition of a comprehensive methodology to quantify the security of a generic system independently from the technology and the environment and ii) the integration of the derived metrics into a closed-loop scheme that allows real-time control of the system. The solution described in this work moves from the proof-of-concepts performed in the early phase of the pSHIELD research and enrich es it through an innovative metric with a sound foundation, able to potentially cope with any kind of pplication scenarios (railways, automotive, manufacturing, ...)

Requirements Specification for Controller Design-from Use Cases to IOPT Net Models

12th IEEE International Conference on Industrial Informatics, INDIN , Porto Alegre: Jul 27-30, 2014Non-autonomous Petri nets offer a language especially adapted for controller specifications. They are typically used in the design phase often with no clear connection to the analysis phase, including requirements specification. This paper shows how use cases can be used to support requirements specification amenable to a direct transformation to IOPT nets, a class of non-autonomous Petri nets. To that end, we propose a set of semi-formal rules for use case descriptions, including use case relationships, which take advantage of the concepts available in IOPT nets, namely input and output signals and events and net addition, a net composition operation

Modeling and Analysis of Stage Machinery Control Systems by Timed Colored Petri Nets

International audienceThis paper presents an approach and successful experience of applying timed colored Petri nets on modeling and analyzing a stage machinery control system. The programmable logic controllers (PLCs) based system is modeled with timing constraints. The compositionality is incorporated in the modeling process of the entire design. The PLC synchronization problem with the interactions of environment is analyzed by the state space analysis method. The case studies demonstrate the effectiveness of the approach

Petri net model decomposition - a model based approach supporting distributed execution

Dissertação apresentada para obtenção do Grau de Doutor em Engenharia Electrotécnica, Especialidade de Sistemas Digitais, pela Universidade Nova de Lisboa, Faculdade de Ciências e TecnologiaModel-based systems development has contributed to reducing the enormous difference between the continuous increase of systems complexity and the improvement of methods and methodologies available to support systems development. The choice of the modeling formalism is an important factor for success-fully increasing productivity. Petri nets proved to be a suitable candidate for being chosen as a system specification language due to their natural support of modeling processes with concurrency, synchronization and resource sharing, as well as the mechanisms of composition and decomposition. Also having a formal representation reinforces the choice, given that the use of verification tools is fundamental for complex systems development. This work proposes a method for partitioning Petri net models into concurrent sub-models, supporting their distributed implementation. The IOPT class (Input-Output Place Transition) is used as a reference class. It is extended by directed synchronous communication channels, enabling the com- munication between the generated sub-models. Three rules are proposed to perform the partition, and restrictions of the proposed partition method are identified. It is possible to directly compose models which result from the partitioning operation, through an operation of model addition. This allows the re-use of previously obtained models, as well as the easy modification of the intended system functionalities. The algorithms associated with the implementation of the partition operation are presented, as well as its rules and other procedures. The proposed methods are validated through several case studies emphasizing control components of automation systems

Describing Structure and Complex Interactions in Multi-Agent-Based Industrial Cyber-Physical Systems

The description of structure and complex interactions in Multi-agent-based Industrial Cyber-physical (MAS-ICPS) systems has been elusively addressed in the literature. Existing works, grounded on model-based engineering, have been successful at characterizing and solving system integration problems. However, they fail to describe accurately the collective and dynamic execution behaviour of large and complex industrial systems, particularly in more discrete production domains, such as: automotive, home appliances, aerospace, food and beverages, etc. In these domains, the execution flow diverts dynamically due to production disturbances, custom orders, fluctuations in demand in mixed model production, faults, quality-control and product rework, etc. These dynamic conditions require re-allocation and reconfiguration of production resources, redirection of production flows, re-scheduling of orders, etc. A meta-model for describing the structure and complex interactions in MAS-ICPS is defined in this paper. This contribution goes beyond the State-Of-The-Art (SOTA) as the proposed meta-model describes structure, as many other literature contributions, but also describes the execution behaviour of arbitrarily complex interactions. The previous is achieved with the introduction of general execution flow control operators in the meta-model. These operators cover, among other aspects, delegation of the execution flow and dynamic decision making. Additionally, the contribution also goes beyond the SOTA by including validation mechanisms for the models generated by the meta-model. Finally, the contribution adds to the current literature by providing a meta-model focusing on production execution and not just on describing the structural connectivity aspects of ICPSs.publishersversionpublishe

Petri net based development of globally-asynchronous locally-synchronous distributed embedded systems

Dissertação para obtenção do Grau de Doutor em Engenharia Electrotécnica e de ComputadoresA model-based development approach (MBDA) for Globally-Asynchronous Locally- Synchronous (GALS) Distributed Embedded Systems (DESs) is proposed. This approach relies on the GALS-DESs specification through (low- or high-level) Petri net classes, which ensure that the created models are GALS, locally deterministic, distributable, networkindependent, and platform-independent and support their simulation, verification, and implementation (using simulation, model-checking, and code generation tools). The use of network- and platform-independent models enable the use of heterogeneous communication networks to support the distributed components interaction and enable the use of heterogeneous platforms to support the components and the communication nodes implementation. To enable the proposed MBDA, Petri nets are extended with a set of the concepts, most notably time-domains and asynchronous-channels. Algorithms to support the verification of GALS-DES models and their decomposition into implementable sub-models are also proposed. A tool chain framework (IOPT-tools) was extended with this work proposals, supporting their validation and the GALS-DESs development.Fundação para a Ciência e a Tecnologia - grant ref. SFRH/BD/62171/200

Purpose and benefits of hybrid simulation: Contributing to the convergence of its definition

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