Hae Sang Song

A Real-Time Discrete Event System Specification Formalismfor Seamless Real-Time Software Development

We present a time domain extension of the hierarchical and modular discrete event specification (DEVS) formalism. This extension is important for establishing a seamless real-time software development framework. Formalisms help describe a system unambiguously. If formal models are implemented without any consistent frameworks, however, it is hard to guarantee that there is no semantic gap between models and codes. Real-Time DEVS, named RTDEVS, is an extension of DEVS that can be characterized in three perspectives: the real time execution of models, the addition of time interval functions, and the activity specification for each state. After analyzing a system, the framework based on RTDEVS helps to expand each model of the system for executing in a real-time environment. In order to support the RTDEVS formalism, we propose abstract executive concepts based on the abstract simulator concepts of the DEVS formalism. Also, we implement an RTDEVS execution engine, named DEVS Executive, which runs on real-time Mach.

DEVS Framework for Modelling, Simulation, Analysis, and Design of Hybrid Systems

We make the case that Discrete Event System Specification (DEVS) is a universal formalism for discrete event dynamical systems (DEDS). DEVS offers an expressive framework for modelling, design, analysis and simulation of autonomous and hybrid systems. We review some known features of DEVS and its extensions. We then focus on the use of DEVS to formulate and synthesize supervisory level controllers.

Application of Real-Time DEVS to Analysis of Safety-Critical Embedded Control Systems: Railroad Crossing Control Example

This article presents an application of the Discrete Event System Specification (DEVS) framework to the design and safety analysis of a real-time embedded control system, a railroad crossing control system. The authors employ an extension of the DEVS formalism, real-time DEVS (RT-DEVS), which has a sound semantics for the specification of real-time systems in a hierarchical modular fashion. The notion of a clock matrix for communicating RT-DEVS models is proposed, which represents a global time between the models. Based on the composition rules and the clock matrix, an algorithm for the generation of a timed reachability tree is developed that can be used for safety analysis at two phases: an untimed and timed analysis phase. A railroad crossing control example demonstrates that the proposed analysis for RT-DEVS models would be effective to verify the safety property of real-time control systems.

Measurement of Effectiveness for an Anti-torpedo Combat System Using a Discrete Event Systems Specification-based Underwater Warfare Simulator

Modeling and simulation (M&S) has long played an important role in developing tactics and evaluating the measure of effectiveness (MOE) for the underwater warfare system. In simulation-based acquisition, M&S technology facilitates decisions about future equipment procurements, such as a mobile decoy or a torpedo. In addition, assessment of submarine tactical development, during an engagement against a torpedo, can be conducted using M&S techniques. This paper presents a case study that applies discrete event systems specification-based M&S technology to develop a simulation of an underwater warfare system, specifically, an anti-torpedo combat system, to analyze the MOE of the system. The entity models required for M&S are divided into three sub-models: controller, maneuver, and sensor model. The developed simulation allows us to conduct a statistical evaluation of the overall underwater warfare system under consideration, an assessment of the anti-torpedo countermeasure’s effectiveness, and an assessment of tactics development of the underwater vehicle. Moreover, it can be utilized to support the decision-making process for future equipment procurements. In order to analyze the system effectiveness, we performed extensive combat experiments by varying parameters, such as various tactics and weapon performance. The experimental results show how the factors influence the MOEs of the underwater warfare system.

The DEVS framework for discrete event systems control

This paper proposes a new methodology for analysis of discrete event systems and design of discrete event systems controllers. The methodology is based on the sound semantics for specification of discrete event systems, called the discrete event system specification (DEVS) formalism. It introduces concepts of inverse DEVS and defines controllability of discrete event systems expressed in the DEVS formalism. These two concepts, inverse DEVS and controllability of discrete event systems, play important roles in designing a discrete event controller. An example for appreciating the concepts is presented.<<ETX>>

MapReduce Based Experimental Frame for Parallel and Distributed Simulation Using Hadoop Platform

Simulation-based experiment of complex systems is a time consuming-job. Parallel and distributed simulation is one of the methods to reduce the simulation time. To simulate and analyze the system with this method, it is required to design a suitable experimental frame. Therefore, this paper proposes a MapReduce based experimental frame for the parallel and distributed simulation. Because Hadoop MapReduce is the most widely used parallel and distributed computing platform, we use it to design the experimental frame. In our work, the ‘map’ of MapReduce automatically generates and simulates the system, and the ‘reduce’ of MapReduce collects and analyzes the result. We can reuse the existing large scale Hadoop clusters without any modification of the platform, so it is easy to set-up and use the experimental frame. This paper presents an air defense simulation to show the usage and speed up with a 16-node Hadoop cluster.

Greenhouse Modeling And Simulation Framework For Extracting Optimal Control Parameters.

In a greenhouse system, a control is important to allow optimal growth conditions for crops. However, because testing the greenhouse for real conditions requires much time and money, the modeling-and-simulation approach is necessary to predict and improve the greenhouse environment. There is much research related to greenhouse control, there is a lack of research on applicable frameworks for real greenhouses. Therefore, this paper proposes a greenhouse modeling-andsimulation framework to extract optimal control parameters. The proposed work is composed of three parts: system identification, controller design, and optimization. The plant model is built through system identification, and the model is controlled by the controller, which is affected by disturbances. This simulation is repeated through design of experiments to optimize the control parameters. This paper presents an experiment with real greenhouse data from Jinju, Korea to show the usefulness of the proposed framework. It gives insight into the decision of choosing control parameters and helps to raise agricultural productivity.

Safety Analysis of Computer-Controlled Real-Time Systems with Message Loss Using Communicating DEVS Models

The Communication DEVS formalism is an analysis means for discrete event systems modeled by DEVS formalism which has been widely used as a system theoretical specification. This paper proposes a new method for analyzing safety of real-time discrete event systems using communicating DEVS formalism. It is a part of efforts toward a unified method for modeling, simulation, and logical analysis based on the DEVS formalism and associate theory. For safety analysis of such real-time discrete event systems we first define communicating DEVS and then propose a timed reachability analysis algorithm for the models. The algorithm visits all possible timed states of the model, which is not always possible by using a simulation based state traversal. The proposed method can be well used especially for DEVS-specified systems to check various logical properties such safety, liveness and so on. A case study of a safety analysis for a rail road crossing system illustrates the usefulness of the proposed method.

Logical Analysis of Real-time Discrete Event Control Systems Using Communicating DEVS Formalism

As complexity of real-time systems is being increased ad hoc approaches to analysis of such systems would have limitations in completeness and coverability for states space search. Formal means using a model-based approach would solve such limitations. This paper proposes a model-based formal method for logical analysis, such as safety and liveness, of real-time systems at a discrete event system level. A discrete event model for real-time systems to be analyzed is specified by DEVS(Discrete Event Systems Specification) formalism, which specifies a discrete event system in hierarchical, modular manner. Analysis of such DEVS models is performed by Communicating DEVS (C-DEVS) formalism of a timed global state transition specification and an associated analysis algorithm. The C-DEVS formalism and an associated analysis algorithm guarantees that all possible states for a given system are visited in an analysis phase. A case study of a safety analysis for a rail road crossing system illustrates the effectiveness of the proposed method of the model-based approach.