Tag Gon Kim

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.

Fast learning method for back-propagation neural network by evolutionary adaptation of learning rates

In training a back-propagation neural network, the learning speed of the network is greatly affected by its learning rate. None, however, has offered a deterministic method for selecting the optimal learning rate. Some researchers have tried to find the sub-optimal learning rates using various techniques at each training step. This paper proposes a new method for selecting the sub-optimal learning rates by an evolutionary adaptation of learning rates for each layer at every training step. Simulation results show that the learning speed achieved by our method is superior to that of other adaptive selection methods.

System entity structuring and model base management

System entity structure (SES) is a structural knowledge representation scheme that contains knowledge of decomposition, taxonomy, and coupling of a system. Formally, the SES is a labeled tree with attached variable types that satisfy certain axioms. Described is a realization of the SES in Scheme (a Lisp dialect), that is called ESP-Scheme. Specifically, the computer representation of SES and main operations on SES are presented, and then facilities provided by ESP-Scheme are described. Two examples of application are discussed: a parallel processor model and a simulation study of a university phone registration system. ESP-Scheme acts as a model base management system in DEVS-Scheme, a knowledge-based simulation environment. It supports specification of the structure of a family of models, pruning the structure to a reduced version, and transforming the latter to a simulation model by synthesizing component models in the model base. >

DEVSim++Toolset for Defense Modeling and Simulation and Interoperation

Discrete Event Systems Specification (DEVS) formalism supports the specification of discrete event models in a hierarchical and modular manner. Efforts have been made to develop the simulation environments for the modeling and simulation (M&S) of systems using DEVS formalism, particularly in defense M&S domains. This paper introduces the DEVSim++ toolset and its applications. The Object-Analysis Index (OAI) matrix is a tabular form of objects and analysis indices for requirements analysis. DEVSim++ is a realization of DEVS formalism in C++ for M&S. VeriTool is a DEVS model verification tool. DEVSimHLA is a library to support High-level Architecture (HLA) in DEVSim++. Other tools, including KComLib, FOM2CPPClass, and KHLAAdaptor, are used to develop a smart adaptor that allows for the interoperation of simulators of any kind. PlugSim is a distributed simulation framework using plug-in methods. These tools are utilized in every stage of the M&S development process, as well as in every application of the M&S missions to the military domain. Accordingly, the applications implemented by the toolset are used in the training, analytic, and acquisition missions of the Republic of Korea military branches. We expect the DEVS applications to become more prolific as M&S demands grow, and our toolset is already proven as complete and efficient in the domain of defense M&S.

The DEVS formalism: hierarchical, modular systems specification in an object oriented framework

This paper describes a realization of DEVS (Discrete Event System Specification) formalism in an object-oriented programming environment, SCOOPS of PC-Scheme. The realization, DEVS-Scheme, is a powerful environment combining simulation modelling with AT techniques, which supports hierarchical, modular specification of discrete event models. We will describe the taxonomical organization of classes in DEVS-Scheme in which kernel-models classes will be emphasized. As an example, we will illustrate specification of kernel models including broadcast models, hypercube models, and cellular models. Finally, implementation of isomorphism checks between pairs of models in DEVS-Scheme will be discussed. Thus, DEVS-Scheme represents a significant step toward implementing system theoretic based formalisms and operations.

An Approach to a Hybrid Software Process Simulation using the DEVS Formalism

This article proposes an approach to a hybrid software process simulation modeling (SPSM) using discrete event system specification (DEVS) formalism, which implements the dynamic structure and discrete characteristics of the software development process. Many previous researchers on hybrid SPSM have described both discrete and continuous aspects of the software development process to provide more realistic simulation models. The existing hybrid models, however, have not fully implemented the feedback loop mechanism of the system dynamics. We define the DEVS Hybrid SPSM formalism by extending DEVS to the hybrid SPSM domain. Our hybrid SPSM approach uses system dynamics modeling to convey details concerning activity behaviors and managerial policies, while discrete event modeling controls activity start/completion and sequence. This approach also provides a clear specification, an explicit extension point to extend the simulation model, and a reuse mechanism. We will demonstrate a Waterfall-like hybrid software process simulation model using the DEVS Hybrid SPSM formalism. Copyright  2006 John Wiley & Sons, Ltd.

Framework for Simulation of Hybrid Systems: Interoperation of Discrete Event and Continuous Simulators Using HLA/RTI

A hybrid system is a combination of discrete event and continuous systems that act together to perform a function not possible with any one of the individual system types alone. A simulation model for the system consists of two sub-models, a continuous system model, and a discrete event model, and interfaces between them. Naturally, the modeling/simulation tool/environment of each sub- model may be different and specific to the model types and the associated modeling formalisms. This paper proposes a framework for simulating hybrid systems by means of interoperation between existing simulators for a continuous model and a discrete event model using a High Level Architecture (HLA). Each simulator is executed using different simulation algorithm, and pre-simulation methodology is applied for synchronization of the different simulators. The main advantage of the proposed approach is the reuse of simulation models, which are developed in their own simulation environments of heterogeneous types. The proposed framework was applied to water level simulation.

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.

A heterogeneous simulation framework based on the DEVS BUS and the high level architecture

We describe a heterogeneous simulation framework in which conventional simulation models and the DEVS (Discrete Event Systems Specification) models can be interoperable. The framework conceptually consists of three layers: the model layer, the DEVS layer, and the HLA (High Level Architecture) layer. The model layer has a collection of heterogeneous simulation models, such as DEVS, CSIM, SLAM, and so on, to represent various aspects of a complex system. The DEVS layer provides a common framework, called the DEVS BUS, so that such simulation models can communicate with each other. Finally, the HLA layer is employed as a communication infrastructure, which supports several good features for distributed simulation. The DEVS BUS has been implemented on the HLA and a simple example of communicating two heterogeneous models has been developed to validate the DEVS BUS.

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.