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In this tutorial review paper we explain the concept of homomorphism and identify some principles that justify homomorphism construction based on the homogeneity of structure and coupling in systems with multiple components. We discuss some simple examples to show how these underlying justifying conditions can arise. Examples include brain simulation, combat attrition, and the greatly reduced computational complexity represented by Pascal's triangle. Homomorphism is also shown to be fundamental for constructing approximate low-resolution models. Models that simplify complex time-demanding simulation models are often used as surrogate or metamodels in system optimization. However, such models are fitted typically to computationally derived response surfaces and not structurally related directly to the originals using homomorphisms as described here. Along these lines, we show how homomorphism plays an essential role in a novel approach being developed to strongly control tree expansion in state space explorations of stochastic system simulation. [ABSTRACT FROM AUTHOR]

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]

This article works toward a unification of two related concepts that underpin system-theory-based modeling and simulation–the hierarchy of system specifications and morphisms and the System Entity Structure (SES). The hierarchy organizes system specification along levels ranging from behavior to structure capturing increasing knowledge of the system input/output processing and state dynamics. The SES is a constructive ontology describing compositions of modular components via coupling of input/output ports. Toward unification of these concepts, we propose an abstraction of the SES called the MetaSES that supports the construction of complex systems of systems with multiple components belonging to specified classes. Moreover, we place the MetaSES within a computational framework with the goal of making it easier to design and build complex hierarchical DEVS models and to communicate their structures and intended behaviors to foster continued reuse and development. We discuss several examples of applications to illustrate how the MetaSES-based enhancement of the hierarchy of system specifications and morphisms helps to push the boundaries of complexity management in the theory and practice of modeling and simulation. Research directions stemming from the proposed concepts are suggested. [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]

In Discrete Event System Specification (DEVS), the dynamics of a network is constituted only by the dynamics of its basic components. The state of each component is fully encapsulated. Control in the network is fully decentralized to each component. At dynamic structure level, DEVS should permit the same level of decentralization. However, it is hard to ensure structure consistency while letting all components achieve structure changes. Besides, this solution can be complex to implement. To avoid these difficulties, usual dynamic structure approaches ensure structure consistency allowing structure changes to be done only by the network having newly added dynamics change capabilities. This is a safe and simple way to achieve dynamic structure. However, it should be possible to simply allow components of a network to modify the structure of their network, other components and/or their own structure - without having to modify the usual definition a DEVS network. In this manuscript, it is shown that a simple fully decentralized approach is possible while ensuring full modularity and structure consistency. [ABSTRACT FROM AUTHOR]

We present an activity-based framework that links information and energy. The activity-based framework uses a quantization-based approach for modeling information processing and defines weighted activity to model the energy consumption of information processing. We provide a formal description of this framework and use simulation to show how it enables one to study the interaction between information and energy in energy-aware information processing. An existing discrete event system specification (DEVS)-based simulation environment, DEVS-FIRE, is employed to model wireless sensor nodes for detecting and monitoring wildfires. Simulation experimental results confirm the utility of the activity-based framework to support the analysis and design of energy-aware information processing systems. [ABSTRACT FROM AUTHOR]

System entity structure has been used since the 1970s as a formal ontology framework, axiomatically defined, to represent the elements of a system of systems and their hierarchical relationships resulting in a family of hierarchical models. One challenge with this approach is the process of exploring a family of hierarchical models, and selecting a particular composition from which a fit-for-purpose discrete-event simulation model can be automatically synthesized and executed. This paper deals with the definition of performance metrics which are used to guide the Modeler to select the most practical model of a real-world system from among a potentially large set. The discrete-event simulation model is selected among a set of system entity structure family models by using model level activity metrics in order to be able to have a prediction of the accuracy and the performance of the models. A case study is presented to illustrate and validate the relation between activity metrics and system entity structure concepts. [ABSTRACT FROM AUTHOR]