Discrete Event System Specification Simulation Research Articles

Mapping RDEVSNL-based Definitions of Constrained Network Models to Routed DEVS Simulation Models

The Routed DEVS (RDEVS) formalism has been introduced recently to provide a reasonable formalization for the simulation of routing processes over Discrete Event System Specification (DEVS) models. Due to its novelty, new software tools are required to improve the Modeling and Simulation (MS) tasks related to the RDEVS formalism. This paper presents the mapping between constrained network models obtained from textual specifications of routing processes and RDEVS simulation models implemented in Java. RDEVSNL context-free grammar (previously defined) is used to support the textual specification of a routing process as a constrained network model. Such grammar is based on a metamodel that defines the syntactical elements. This metamodel is used in this paper as a middleware that allows mapping constrained network model concepts with RDEVS simulation models. From such a constrained network model template, RDEVS Java implementations are obtained. The proposal is part of a work-in-progress intended to develop MS software tools for the RDEVS formalism using well-known abstractions to get the computational models through conceptual mapping. Using these tools, modelers can specify simulation models without needing to codify any routing implementation. The main benefits are i) reduction of implementation times and ii) satisfactory simulation model correctness regarding the RDEVS formalism.

Combining DEVS simulation and ontological modeling for hierarchical analysis of the SARS-CoV-2 replication

This article presents an hybrid and hierarchical model in which two modeling and simulation approaches, discrete event system specification simulation (DEVS) and semantic technologies, were used together in order to help in the analysis of a major healthcare problem, the severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2). Indeed, the complexity of the SARS-CoV-2 replication process, and the range of hierarchical scales over which it interacts with cellular components (extending from genomic and transcriptomic to proteomic and metabolomic scales), and the intricate way in which they are interwoven, make its understanding very challenging. It is therefore crucial to model the different scales of the replication process, by taking into account all interactions with the infected cell. By combining the advantages of both DEVS simulation and ontological modeling, we propose a hierarchical ontology-based DEVS simulation model of the SARS-CoV-2 viral replication at both the micro-molecular (proteomic and metabolomic) and macro-molecular (genomic and transcriptomic) scales. First, we demonstrate the usefulness of combining DEVS simulation and semantic technologies in a common modeling framework to face the complexity of the SARS-CoV-2 viral replication at different scales. Second, the modeling and simulation of the SARS-CoV-2 replication process on different levels provide valuable information on the different stages of the virus’s life cycle and lays the foundation for a system to anticipate future mutations selected by the virus.

XDEVS: A hybrid system modeling framework

When Discrete Event System Specification (DEVS) is used as a modeling tool, there is a semantic gap between a DEVS model and the mathematical representation, which may result in understanding difficulties. To provide a more intuitive form of modeling, XDEVS expands the concept of states in DEVS. The continuous state is introduced in XDEVS, which enhances the ability to model hybrid systems. Based on the DEVS simulation framework, a simulation engine is developed to drive the XDEVS model safely and efficiently and avoid the wrong location of state events during the simulation of the continuous model. A hybrid model is constructed and simulated using XDEVS. A comparison between the XDEVS model and models described by DEV&DESS and GDEVS shows that XDEVS can clearly express the structure of the model and reduce the burden on modelers.

Metamodel-based formalization of DEVS atomic models

The Discrete-Event System Specification (DEVS) formalism is a modeling formalism based on systems theory that provides a general methodology for hierarchical construction of reusable models in a modular way. When concrete DEVS models are developed using programming languages, it is difficult to ensure they conform to their formal model. Hence, building an implementation of formal models in a way that ensures DEVS formalism correctness is not easy. In this paper, we improve the interplay of abstraction (i.e., formal specification) and concreteness (i.e., programming code implementation) in advancing the theory and practice of DEVS using a specific-designed metamodel. The main contribution is a novel conceptualization of classic DEVS with ports founded on existing approaches but that also includes new improved elements related to the definition of atomic models. That is, our metamodel includes all the concepts and relationships needed to define the formal specification of DEVS atomic models. This allows us to define instances of our conceptualization that comply with the DEVS formal specification. To instantiate our metamodel, we propose a computer-aided environment that has been developed using the Eclipse Modeling Project. As an example, we show how our metamodel can be used to define the classic “switch” model. As a conclusion, we discuss how the final metamodel can be used to support interoperability with DEVS simulation tools.

A simulation-driven online scheduling algorithm for the maintenance and operation of wind farm systems

Wind turbines experience stochastic loading due to seasonal variations in wind speed and direction. These harsh operational conditions lead to failures of wind turbines, which are difficult to predict. Consequently, it is challenging to schedule maintenance actions that will avoid failures. In this article, a simulation-driven online maintenance scheduling algorithm for wind farm operational planning is derived. Online scheduling is a suitable framework for this problem since it integrates data that evolve over time into the maintenance scheduling decisions. The computational study presented in this article compares the performance of the simulation-driven online scheduling algorithm against two benchmark algorithms commonly used in practice: scheduled maintenance and condition-based monitoring maintenance. An existing discrete event system specification simulation model was used to test and study the benefits of the proposed algorithm. The computational study demonstrates the importance of avoiding over-simplistic assumptions when making maintenance decisions for wind farms. For instance, most literature assumes maintenance lead times are constant. The computational results show that allowing lead times to be adjusted in an online fashion improves the performance of wind farm operations in terms of the number of turbine failures, availability capacity, and power generation.

Method for Detecting Modification of Transmitted Message in C/C++ Based Discrete Event System Specification Simulation

Method for Detecting Modification of Transmitted Message in C/C++ Based Discrete Event System Specification Simulation

XML-based DEVS modelling and simulation tracking

Discrete event system specification (DEVS) is a modelling and simulation formalism for discrete event dynamic systems. DEVS has known different variants and software implementations to meet specific needs. Unfortunately, these implementations do not necessarily share models and cannot capitalise on model reuse and data exchange. XML, as a meta-language, seems to be an appropriate language for helping modellers with weak programming knowledge. Indeed, XML is adopted as a standard for information exchange and knows an increasingly important use on the web. This work aims at determining an XML-based implementation of DEVS for devising an efficient modelling and simulation framework. After defining and validating our XML schemas, an execution step of these models is defined based on our XML abstract simulator which executes a set of XSLT transformations and generates an XML simulation tree describing the different steps of the system during the simulation time.

Accelerated DEVS Simulation Using Collaborative Computation on Multi-Cores and GPUs for Fire-Spreading IoT Sensing Applications

Discrete event system specification (DEVS) has been widely used in event-driven simulations for sensor-driven Internet of things (IoT) applications, such as monitoring the spread of fire disaster. Event-driven models for IoT sensor nodes and their communication is described in DEVS and they have to be integrated with continuous models of fire-spreading dynamics so that the hybrid system modeling and simulation approach have to be considered for both continuous behavior of fire-spreading and event-driven communications by large-scale IoT sensor devices. The hybrid-integrated modelling and simulation for fire-spreading in wide area and large-scale IoT devices result in more complex model evaluation, including simulation time synchronization, so that simulation acceleration is important by considering scalability in large-scale IoT-driven applications that sense fire-spreading. In this study, we proposed a scalable simulation acceleration of a DEVS-based hybrid system using heterogeneous architecture based on multi-cores and graphic processing units (GPUs). We evaluated the power consumption comparison of the proposed accelerated-simulation approach in terms of the composition of the event-driven IoT models and continuous fire-spreading models, which are tightly described in differential equations across a large number of cellular models. The demonstrated result shows that the full utilization of CPU-GPU integrated computing resources, on which event-driven models and continuous models are efficiently deployed and optimally distributed, could enable an advantage for high-performance simulation speedup in terms of execution time, although more power consumption is required, but the total energy consumption could be reduced due to fast simulation time.

A novel multi-level evaluation approach for human-coupled IoT applications

The recent emerging trend to promote the harmonious interactions between human and smart objects in Internet of Things (IoT) applications has led to the rising demand for the comprehensive exploration of associated IoT design spaces, considering system-, network-, and human-level perspectives. The traditional design approach of networked smart objects tends to ignore the effects caused by human interactions so that the existing approach has the limited capability in joint system/network/human multi-level exploration. In this paper, we propose a high-level system modeling and multi-level simulation approach for microsystem models to interoperate with high-level models in the human-level perspective and to provide comprehensive co-exploration. The high-level system modeling enables one to abstract the detailed operations of hardware platforms using power and timing data obtained by the proposed high-level state-based profiling method and using the event-driven modeling concept. For the event-driven system modeling, we utilize the discrete-event system specification (DEVS) to support scalable model-driven prototyping. To represent the coupled relationship of network-level system activity and human-level interactions between node systems and humans, we employ a general-purpose network simulator to model the operation and communication of network modules in smart objects and developed agent-based human behavioral models. For the co-simulation of multi-level models, we designed a distributed simulation platform to enable the interoperation between the DEVS simulator and the network simulator using a runtime infrastructure. The proposed modeling and simulation approach is applied for the multi-level evaluation of a smart museum application to estimate the effect of energy-efficiency policies.

Increasing the performance of a Discrete Event System Specification simulator by means of computational resource usage “activity” models

Domain-specific simulators often have an edge on general-purpose simulators in terms of performance. Their intricate knowledge of the domain allows them to aggressively optimize and take shortcuts. In contrast, simulators for more general formalisms, such as Discrete Event System Specification (DEVS), need to support a wider set of models. Their inability to use domain information prevents DEVS simulators from achieving as high performance as their domain-specific variants. To solve this problem, we introduce a way to enhance the simulation performance of DEVS models through the use of computational resource usage models, often termed “activity” models. These models augment general-purpose DEVS models with domain-specific information, which can be used by the simulator. We apply this information in the context of data structure optimization, load balancing, and model allocation. Activity-awareness is a non-invasive extension to the DEVS formalism, meaning that activity-augmented models remain perfectly valid for use in activity-unaware simulators. Similarly, models without activity can still be simulated by an activity-aware simulator. Our approach is validated by making PythonPDEVS, a Parallel DEVS simulator, activity-aware and evaluating the performance impact on a set of benchmark models.

Using the Parallel DEVS Protocol for General Robust Simulation with Near Optimal Performance

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.

Reconsidering the performance of DEVS modeling and simulation environments using the DEVStone benchmark

The discrete event system specification formalism, which supports hierarchical and modular model composition, has been widely used to understand, analyze and develop a variety of systems. Discrete event system specification has been implemented in various languages and platforms over the years. The DEVStone benchmark was conceived to generate a set of models with varied structure and behavior, and to automate the evaluation of the performance of discrete event system specification-based simulators. However, DEVStone is still in a preliminary phase and more model analysis is required. In this paper, we revisit DEVStone introducing new equations to compute the number of events triggered. We also introduce a new benchmark with a similar central processing unit and memory requirements to the most complex benchmark in DEVStone, but with an easier implementation and with it being more manageable analytically. Finally, we compare both the performance and memory footprint of five different discrete event system specification simulators in two different hardware platforms.

System entity structure extension to integrate abstraction hierarchies and time granularity into DEVS modeling and simulation

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.

Enhancing the reusability and interoperability of artificial neural networks with DEVS modeling and simulation

Artificial neural networks (ANNs), a branch of artificial intelligence, has become a very interesting domain since the eighties when back-propagation (BP) learning algorithm for multilayer feed-forward architecture was introduced to solve nonlinear problems. It is used extensively to solve complex nonalgorithmic problems such as prediction, pattern recognition and clustering. However, in the context of a holistic study, there may be a need to integrate ANN with other models developed in various paradigms to solve a problem. In this paper, we suggest discrete event system specification (DEVS) be used as a model of computation (MoC) to make ANN models interoperable with other models (since all discrete event models can be expressed in DEVS, and continuous models can be approximated by DEVS). By combining ANN and DEVS, we can model the complex configuration of ANNs and express its internal workings. Therefore, we are extending the DEVS-based ANN proposed by Toma et al. [A new DEVS-based generic artficial neural network modeling approach, The 23rd European Modeling and Simulation Symp. (Simulation in Industry), Rome, Italy, 2011] for comparing multiple configuration parameters and learning algorithms and also to do prediction. The DEVS models are described using the high level language for system specification (HiLLS), [Maïga et al., A new approach to modeling dynamic structure systems, The 29th European Modeling and Simulation Symp. (Simulation in Industry), Leicester, United Kingdom, 2015] a graphical modeling language for clarity. The developed platform is a tool to transform ANN models into DEVS computational models, making them more reusable and more interoperable in the context of larger multi-perspective modeling and simulation (MAS).

Efficient Flattening Algorithm for Hierarchical and Dynamic Structure Discrete Event Models

Discrete event models are widely used to replicate, analyze, and understand complex systems. DEVS (Discrete Event System Specification) formalism enables hierarchical modeling, so it provides an efficiency in the model development of complex models. However, the hierarchical modeling incurs prolonged simulation executions due to indirect event exchanges through the model hierarchy. Although direct event paths are applied to mitigate this overhead, the situation becomes even worse when a model changes its structures during simulation execution, called a dynamic structure model. This article suggests Coupling Relation Graph (CRG) and Strongly Coupled Component (SCC) concepts to improve hierarchical and dynamic structure DEVS simulation execution. CRG is a directed graph representing DEVS model structure, and SCC is a group of connected components in a CRG. Using CRG and SCC, this article presents (1) how to develop CRG from a DEVS model and (2) how to construct and update direct event paths with respect to dynamic structural changes. In particular, compared to the previous works, the proposed method focuses on the reduction of the updating costs for the direct event paths. Through theoretical and empirical analyses, this article shows that the proposed method significantly reduces the simulation execution time, especially when a simulation model contains lots of components and changes its model structures frequently. We expect that the proposed method would support the faster simulation executions of complex hierarchical and dynamic structure models.

Construction of Concurrent Programs Based on a Modeling and Simulation Formalism

This paper proposes a framework for developing a concurrent program using the discrete event system specification (DEVS) formalism. Within the proposed framework, a concurrent program is modeled by the DEVS formalism, and the modeling result is validated through simulation in a DEVS abstract simulator environment, called DEVSim++. Then, the validated modeling results are translated to multi-threaded program codes written in a conventional programming language. For that, each DEVS model which specifies behavior of a component is converted to a single thread, called an atomic thread, and every connection information between the components are clustered together and converted to a data structure, called a port mapping table. This paper also proposes an efficient solution which combines several atomic threads into a new thread, called a combined thread.

Action-level real-time DEVS modeling and simulation

For some classes of systems, it is advantageous to develop real-time models instead of step-wise or logical-time models. Toward this goal, the action-level real-time (ALRT) discrete-event system specification (DEVS) modeling and simulation approach is proposed. Modeling of actions is introduced into the parallel DEVS formalism using time invariants defined for real-time statecharts. Actions are specified in terms of time-windows that are to be executed in real-time. An abstract simulator protocol is devised for executing the ALRT-DEVS models under constrained computational resources. The approach is implemented in the parallel DEVS-Suite simulator. These models can be simulated on unitary computing platforms. A simple example switch model is detailed and tested to show the kinds of real-time modeling and simulation studies that can be supported.

Designing DEVS visual interfaces for end-user programmers

Although the Discrete Event System specification (DEVS) has over recent decades provided systems engineers with a scalable approach to modeling and simulation, the formalism has seen little uptake in many other disciplines where it could be equally useful. Our observations of end-user programmers confronted with DEVS theory or software suggest that learning barriers are largely responsible for this lack of utilization. To address these barriers, we apply ideas from human–computer interaction to the design of visual interfaces intended to promote their users’ effective knowledge of essential DEVS concepts. The first step is to propose a set of names that make these concepts easier to learn. We then design and provide rationale for visual interfaces for interacting with various elements of DEVS models and simulation runs. Both the names and interface designs are evaluated using the Cognitive Dimensions of Notations framework, which emphasizes trade-offs between 14 aspects of information artifacts. As a whole, this work illustrates a generally applicable design process for the development of interactive formalism-based simulation environments that are learnable and usable to those who are not experts in simulation formalisms.

An integrated framework for automated simulation of SysML models using DEVS

System models are constructed to design, study, and understand complex systems. According to the systems modeling language (SysML) that is a standard for model-based system engineering, all engineering activities should be performed using a common model. To validate complex system models defined in SysML, simulation is usually employed. There are numerous efforts to simulate SysML models using different simulation methods and tools. However, the efficient support of automated generation of executable simulation code is still an issue tangled by the research community. This paper introduces DEVSys, an integrated framework for utilizing existing SysML models and automatically producing executable discrete event simulation code, according to model driven architecture (MDA) concepts. Although this approach is not simulation-specific, discrete event system specification (DEVS) was employed, due to the similarities between SysML and DEVS, mainly in system structure description, and the mature, yet ongoing research on expressing executable DEVS models in a simulator-neutral manner. DEVSys framework elements include (a) a SysML profile for DEVS, enabling integration of simulation capabilities into SysML models, (b) a meta-model for DEVS, allowing the utilization of MDA concepts and tools, (c) a transformation of SysML models to DEVS models, using a standard model transformation language as query/view/transform (QVT), and (d) the generation of DEVS executable code for a DEVS simulation environment with an extensible markup language (XML) interface. The definition and implementation of DEVSys elements, as well as the process for its application are demonstrated and discussed, with the aid of a simple working example.

홈 네트워크 기반에서 멀티미디어 공동 작업 공간을 위한 화이트보드

본 논문은 홈 네트워크 기반에서 멀티미디어 공동 작업 공간을 위한 화이트보드에 대해서 제안하였다. 본 시스템은 공동 작업에 참여한 사용자들이 다른 참여자들에게 같은 뷰로써 공유된 미디어들을 참조할 수 있도록 구축한다. 본 논문에서는 화이트보드를 통하여 미디어 데이터의 신뢰성을 향상시키는 방법에 대해서 기술한다. 본 논문은 규칙-기반 DEVS(Discrete Event System Specification) 모델링과 시뮬레이션 기법을 사용하면서 분산 멀티미디어 상에서 화이트보드를 이용한 미디어 데이터 시스템의 성능 분석을 설명한다. This paper suggested a whiteboard for multimedia collaboration work. We implemented the whiteboard so that the users participated in collaborative work may refer shared media objects as the same view to others. In this paper, we discuss a method for increasing reliability of media data through whiteboard. This paper explains a performance analysis of a media data system running on distributed multimedia environment using the rule-based DEVS modeling and simulation techniques.