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Paratemporal methods based on tree expansion have proven to be effective in efficiently generating the trajectories of stochastic systems. However, combinatorial explosion of branching arising from multiple choice points presents a major hurdle that must be overcome to implement such techniques. In this paper, we tackle this scalability problem by developing a systems theory-based framework covering both conventional and proposed tree expansion algorithms for speeding up discrete event system stochastic simulations while preserving the desired accuracy. An example is discussed to illustrate the tree expansion framework in which a discrete event system specification (DEVS) Markov stochastic model takes the form of a tree isomorphic to a free monoid over the branching alphabet. We derive the computation times for baseline, non-merging, and merging tree expansion algorithms to compute the distribution of output values at any given depth. The results show the remarkable reduction from exponential to polynomial dependence on depth effectuated by node merging. We relate these results to the similarly reduced computation time of binomial coefficients underlying Pascal's triangle. Finally, we discuss the application of tree expansion to estimating temporal distributions in stochastic simulations involving serial and parallel compositions with potential real-world use cases. [ABSTRACT FROM AUTHOR]

Featured Application: This research contributes toward the theoretical foundations of model-based systems engineering (MBSE) through combining the mathematical, system theoretic framework for MBSE developed by A. Wayne Wymore with the computational systems theory of Discrete Event System Specification (DEVS). This research leads to internally consistent, holistic modeling and simulation-based systems engineering and a science to MBSE. The objective of this research article is to re-introduce some of the concepts provided by A. Wayne Wymore in his mathematical theory of Model-Based Systems Engineering, discuss why his framework might have not been adopted, and define a potential path to modernize the framework for practical application in the digital age. The dense mathematical theory has never been converted to a practical form. We propose a path to modernization by creating a metamodel of Wymore's mathematical theory of MBSE. This enables explaining the concepts in simple to understand terms and shows the internal consistency provided by the theory. Furthermore, the metamodel allows for conversion of the theory into software application, for which we show some initial results that open the research to the art of the possible. In recognition of limitation of the theory, we make the case for a merger of the theoretical framework with the enhanced formalism of Discrete Event System Specification (DEVS). This will establish a path toward the scientific foundations for MBSE to enable future implementations of the complementary pairing and their empirical results. [ABSTRACT FROM AUTHOR]

The Discrete Event Systems Specification (DEVS) formalism has been widely disseminated in this magazine and elsewhere for its applicability to computational science and engineering. While research in parallel and distributed simulation has been active in the past several decades, the utility of many techniques for high-performance DEVS simulation has been limited. Recent research has shown that that a reconstruction of Amdahl's and Gustafson's laws for parallelizing sequential code can afford a better understanding of the underlying principles and their application to simulation of DEVS models. In this article, the author shows, in comparison to the ideal case, that a relatively simple protocol based on the DEVS abstract simulator is both generally applicable and able to achieve significant speedup in parallel distributed simulation. [ABSTRACT FROM PUBLISHER]

The modeling and simulation (M&S) of complex systems often requires models described at different levels of detail characterized by differences in abstraction hierarchies and/or time granularity. The discrete-event system specification (DEVS) is a framework based on mathematical systems theory that offers a computational basis for application of M&S to systems engineering and that has become widely adopted for its support of discrete-event, continuous, and hybrid applications. A fundamental representation of DEVS hierarchical modular model structures is the system entity structure (SES), which represents a design space via the elements of a system and their relationships in a hierarchical and axiomatic manner. As has been described in a number of publications, the SES supports development, pruning, and generation of DEVS simulation models. The goal of this paper is to propose an extension of SES in order to integrate both the concepts of abstraction hierarchies and time granularity into DEVS. This paper explains in detail: (i) the concepts of abstraction hierarchies and time granularity; (ii) the extension of SES in order to take into account these concepts; (iii) DEVS M&S of complex systems according to different levels of detail (abstraction hierarchies and time granularity); (iv) the use of a Python DEVS simulator (DEVSimPy) to implement the management of abstraction hierarchies and time granularity. A real case study is given to illustrate the proposed approach, and follow-on research needed to implement the concepts is discussed. [ABSTRACT FROM AUTHOR]

Currently, the widely used notion of activity is increasingly present in computer science. However, because this notion is used in specific contexts, it becomes vague. Here, the notion of activity is scrutinized in various contexts and, accordingly, put in perspective. It is discussed through four scientific disciplines: computer science, biology, economics, and epistemology. The definition of activity usually used in simulation is extended to new qualitative and quantitative definitions. In computer science, biology and economics disciplines, the new simulation activity definition is first applied critically. Then, activity is discussed generally. In epistemology, activity is discussed, in a prospective way, as a possible framework in models of human beliefs and knowledge. [ABSTRACT FROM PUBLISHER]

AW Wymore, the founder of the world’s first systems engineering department at the University of Arizona, has been at the origin of the system theoretic foundations of modeling and simulation. Wymore’s intellectual family tree, which goes back to Gauss and Weierstrass, is given. How the authors met, cooperated, and advocated system theory for the advancement of modeling and simulation are explained. The concept of model-based simulation was also one of the outcomes of this cooperation. This article reviews the emergence of systems-theory-based modeling and simulation languages and environments, such as the General System Theory implementor and Discrete Event System Specification, and their relation to Wymore’s concepts. We also discuss the application of powerful software development frameworks to support user-friendly access to systems concepts and to increase the power to support systems design and engineering. [ABSTRACT FROM PUBLISHER]

Cellular automata were designed by John von Neumann in the 1940s, as a mathematical abstraction for modeling self-replicating algorithms. Since then, cellular automata have been widely studied theoretically and evolved into multiple variants. In the 1970s, Bernard P. Zeigler proposed a formalism rooted on systems theory principles, named DEVS (discrete-event systems specifications), which paved the way for component-based modeling and simulation and related methodologies. The purpose of this article is to survey how cellular automata and its variant, called cell-DEVS, may be used to implement computer simulations that can be used as digital serious games. The authors illustrate that implementation through some of the practical applications of such cellular automata. They show various serious game applications using real case studies: first, a simple bouncing ball and pinball game, a particle collision model, another on gossip propagation, and an application on human behavior at a metro station.Then, they show an application to social simulation using a voters game, a theoretical application (a model called Daisy World, which is derived from Gaia theory), and applications to physical phenomena such as a sandpile formation model or, finally, a three-dimensional model of a “virtual clay” that changes its shape when it is subject to pressure effects. [ABSTRACT FROM AUTHOR]

Discrete Event Specification (DEVS) environments are implemented over middleware systems such as HLA, RMI, CORBA and others. DEVS exhibits concepts of systems theory and modeling and supports capturing the system behavior from the physical and behavioral perspectives. Further, they are implemented using object-oriented languages like Java and C++. This research work uses the Java platform to implement DEVS over a Service Oriented Architecture (SOA) framework. Called the DEVS/SOA, the framework supports a development and testing environment known as DEVS Unified Process that is built on a model continuity-based lifecycle methodology. DEVS Unified Process allows DEVS-based Modeling and Simulation (M&S) over net-centric platforms using DEVS/SOA. This framework also provides the crucial feature of run-time composability of coupled systems using SOA. We describe the architecture and designs of the server and the client. The client application communicates with multiple servers hosting DEVS simulation services. These simulation services are developed using the proposed symmetrical services architecture wherein the server can act as both a service provider and a service consumer contrary to the unidirectional client--server paradigm. We also discuss how this services-based architecture provides solutions for cross-platform distributed M&S. We demonstrate the DEVS/SOA framework with a scenario of Joint Close Air Support specified in Business Process Modeling Notation (BPMN). We also provide a realworld application of network health monitoring using DEVS/SOA-layered architectural framework. [ABSTRACT FROM AUTHOR]

Perceiving agents have a limited sensitivity to distinguish input stimuli. Whatever the cause random noise, limited numbers of sensing elements, intentional desensitization formulation of such behavioral phenomena at the system level has not attracted much interest. This work is a first attempt to formalize the limited-sensitivity abstraction and to explore its implications for systems modeling and simulation, both conceptual and practical. In this article, a system theoretic formalization of perceiving agents called quantized systems is provided, linking them with discrete event modeling paradigms and exploring their approximation capability and message reduction in distributed simulation. [ABSTRACT FROM AUTHOR]

The multifaceted modeling methodology discussed in this article is an approach to simulation modeling that realizes that reality is complex, and that, although this complexity is not reducible, partial models can be constructed to aid decision making. This methodology recognizes the need to integrate partial knowledge and solutions obtained under the constraints imposed by disciplinary or problem-oriented perspectives. Various concepts that facilitate this integration are reviewed. [ABSTRACT FROM AUTHOR]