离散事件系统规范DEVS研究

离散事件系统是一类常见的系统,如何对这类系统进行描述与建模是离散事件系统仿真研究的核心内容。离散事件系统规范DEVS是一种离散事件系统形式化描述方法,它具有层次化和模块化的特点,利用该方法可对复杂的离散事件系统进行建模、设计、分析和仿真。该文详细介绍了DEVS基本模型和耦合模型,给出了DEVS在耦合运算下的封闭性构造证明,并提出了一种具有嵌套层次结构的DEVS耦合模型实现算法,该算法对基于DEVS描述的离散事件系统的仿真实现具有一定参考价值。     

Maneuvering control simulation of underwater vehicle based on combined discrete-event and discrete-time modeling

When designing or acquiring underwater vehicles such as submarines and torpedoes, it is necessary to predict their performance precisely and perform tests repeatedly using modeling and simulation at both the engineering level and the tactical engagement level. For simulation performed for analysis purposes at the engineering level, which requires a considerable amount of computation power, a discrete-time system simulation that computes significant values at every single unit time using the established mathematical model or engineering model is mainly employed. To simulate a complex or complicated task such as a traffic analysis or tactical measure of effectiveness (MOE) analysis at the engagement level, it is appropriate to use a discrete-event system simulation that causes transition between model states through the triggering of events on the basis of the passing of messages between simplified mathematical models coupled in various ways. In this paper, we studied a maneuvering control of underwater vehicle from the perspective of a combined discrete-event and discrete-time system simulation; the simulation model is established on the basis of discrete-event system specification (DEVS) formalism, which is a representative modeling formalism of a discrete-event system simulation. In detail, the simulation includes DEVS modeling implementations of simulation execution time control and discrete-time step size control in real time at the time of performing a discrete-time system simulation for the purpose of three-dimensional visualization or carrying out a performance analysis using the DEVS model. This hybrid approach makes possible to build a simulation-based expert system which supports the decision making for the acquisition of an underwater vehicle.     

Knowledge-based environment for investigating multicomputer architectures

Multicomputers for massively parallel processing will eventually employ billions of processing elements, each of which will be capable of communicating with every other processing element. A knowledge-based modelling and simulation environment (KBMSE) for investigating such multicomputer architecture at a discrete-event system level is described. The KBMSE implements the discrete-event system specification (DEVS) formalism in an object-oriented programming system of Scheme (a dialect), which supports building models in a hierarchical, modular manner, a systems-oriented approach not possible in conventional simulation languages. The paper presents a framework for knowledge-based modelling and simulation by exemplifying modelling a hypercube multicomputer architecture in the KBMSE. The KBMSE has been tested on a variety of domains characterized by complex, hierarchical structures such as advanced multicomputer architectures, local area computer networks, intelligent multi-robot organizations, and biologically based life-support systems.     

Ordering of simultaneous events in distributed DEVS simulation

Simultaneous events are the events scheduled to occur at the same simulation time. This paper proposes a new event ordering mechanism for handling simultaneous events of DEVS models in distributed simulation. The DEVS formalism provides a formal framework for specifying discrete event models in a modular, hierarchical form. Thus, the formalism can ease the model verification and validation problems of distributed simulation. Also, the formalism separates models from underlying simulation algorithms. Hence, DEVS models can be simulated in both sequential and distributed environments without any modification. One important issue for such framework is to obtain the same results in both simulation environments. However, in distributed simulation of DEVS models, the processing order of simultaneous events may affect the simulation results. Thus, some ordering mechanism of events is required for well-defined simulation results. The proposed mechanism orders simultaneous events correctly with respect to their causal relationships in distributed DEVS simulation. Also, the mechanism guarantees the same ordering of simultaneous events in both sequential and distributed simulation environments.     

Hybrid system modeling using the SIMANLib and ARENALib Modelica libraries

The ARENALib and SIMANLib Modelica libraries replicate the basic functionality of the Arena simulation environment and the SIMAN language. These libraries facilitate describing discrete-event models using the Arena modeling methodology. ARENALib and SIMANLib models can be combined with other Modelica models in order to describe complex hybrid systems (i.e., combined continuous-time and discrete-event systems). The implementation and design of SIMANLib and ARENALib is discussed. The ARENALib components have been built in a modular fashion using SIMANLib. The SIMANLib components have been described as Parallel DEVS models and implemented using DEVSLib, a Modelica library previously developed by the authors to support the Parallel DEVS formalism. The use of Parallel DEVS as underlying mathematical formalism has facilitated the development and maintenance of SIMANLib. The modeling of two hybrid systems is discussed to illustrate the features and use of SIMANLib and ARENALib: firstly, a soaking-pit furnace; secondly, the malaria spread and an emergency hospital. DEVSLib, SIMANLib and ARENALib can be freely downloaded from http://www.euclides.dia.uned.es/.     

A Real-Time Discrete Event System Specification Formalism for 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.     

REALIZATION THEORY OF DISCRETE-EVENT SYSTEMS AND ITS APPLICATION TO THE UNIQUENESS AND UNIVERSALITY OF DEVS FORMALISM

Many man-made systems have discrete event nature. Many modeling formalisms for discrete-event mechanisms have invented and been used for many problems. Among those models, the DEVS formalism is to provide natural and universal models in some sense.

This paper first provides a realization theory of general discrete-event systems. That is, a behavioral definition of discrete-event system is defined, and then a state transition function of the system is constructed. Based on the realization, the uniqueness problem of representations for discrete-event systems is positively solved. Furthermore, as an application of that solution, this paper shows both the fact that a legitimate DEVS with surjective internal transition function is unique up to isomorphism in the class of state representations of the state system defined from the DEVS, and the fact that any discrete-event system has a DEVS realization. In this sense the DEVS modeling facility has the uniqueness and universality in modeling discrete event mechanisms.     

Extending the DEVS formalism for massively parallel simulation

The use of multiprocessors for discrete event simulation is an active research area where work has focused on strategies for model execution with little regard for the underlying formalism in which models may be expressed. However, a formalism-based approach offers several advantages including the ability to migrate models from sequential to parallel platforms and the ability to calibrate simulation architectures to model structural properties. In this article, we extend the DEVS (discrete event system specification) formalism, originally developed for sequential simulation, to accommodate the full potential of parallel processing. The extension facilitates exploitation of both internal and external event parallelism manifested in hierarchical, modular DEVS models. After developing a mapping of the extended formalism to parallel architectures, we describe an implementation of the approach on a massively parallel architecture, the Connection Machine. Execution results are discussed for a class of models exhibiting high external and internal event parallelism, the so-called broadcast models. These verify the tenets of the underlying theory and demonstrate that significant reduction in execution time is possible compared to the same model executed in serial simulation.     

DEVS methodology for evaluating time-constrained message routing policies

Due to its ability to support temporal issues of systems, discrete event simulation is widely applicable to real-time system design. This paper presents a methodology for the modeling and simulation of time-constrained message routing policies for hypercube interconnected real-time systems. The methodology is based on a framework called the DEVS (discrete event systems specification) formalism which supports modular and hierarchical specification of discrete event models. Within the methodology, we first develop DEVS specification for models for hypercube computers and experimental frames to measure the performance of alternative message routing policies. We then implement such specification in DEVSIM++, a C++-based modeling/simulation environment that implements the DEVS formalism. Simulations of various message routing policies are performed, and the performances of such policies are compared.     

DEVS formalism: a framework for hierarchical model development

A methodology is being developed to map hierarchical, modular discrete event models onto distributed simulator architectures. Concept developed for the first step of the methodology concerning model representation are discussed. The DEVS (Discrete Event System Specification) is extended to facilitate modular, hierarchical model specification. Procedures for top-down model development are expressed with the extended formalism and illustrated with a computer system model design     

DEVSpecL: DEVS specification language for modeling,simulation and analysis of discrete event systems

Discrete EVent Systems Specification (DEVS) formalism supports specification of discrete event models in a hierarchical modular manner. This paper proposes a DEVS modeling language called DEVS Specification Language (DEVSpecL) based on which discrete event systems are modeled, simulated and analyzed within a DEVS-based framework for seamless systems design. Models specified in DEVSpecL can be translated in different forms of codes by code generators, which are executed with various tools for models verification, logical analysis, performance evaluation, and others.     

Hierarchical simulation model with animation

There are many issues in computer simulation such as verifying model code, validating models, understanding the dynamics of systems and training the personnel. The developers of simulation tool have been interested in the animation, since it can help solve theproblems related to the above listed issues. Trying to display all the graphic objects representing the dynamics of the models being simulated, however, causes the distractionof focus, which results in solving the above listed problems difficult. The redundant graphic objects also increase the computer computation overhead. This paper presents a hierarchical animation environment in which the users can have better focus on the dynamics of system components by selectively choosing the hierarchical level and components within a level of the hierarchically structured model. When the model is large and complex in particular, the selection of observation level is needed. The design of the hierarchical animation is based on the DEVS (Discrete EVent system Specification) formalism, which is theoretically well grounded means of expressing modular and hierarchical models.     

A review of: “FRACTALS EVERYWHERE”, by Michael Barnsley,Academic Press,San Diego,California, USA 1988

The modelling and analysis of multi-component discrete event systems is a challenging research area. Over 30 years, modelling and simulation research of discrete event system specification (DEVS) has been developed with (1) dense-time, (2) the I/O concept, and (3) hierarchical model construction. Nevertheless, DEVS model verification research began relatively recently considering the whole DEVS research history. In the meantime, over 15 years, the automata theory has been developed to cover the dense-time behaviour verification of discrete event systems. Especially, timed automata (TA) has performed the key role in the field.

This paper builds on the research results that have been achieved from both theories of DEVS and TA. Thus contributions of this paper can be seen from each side. From the viewpoint of the DEVS theory, a finite and nondeterministic DEVS has been found as a verifiable class. From the viewpoint of the TA theory, a TA which is modular and hierarchical as well as verifiable, is proposed. To show the results, this paper uses the top down manner in which a general formalism is defined first and then its sub-classes are introduced.     

Distributed simulation of DEVS and Cell-DEVS models in CD++ using Web-Services

Discrete event system specification (DEVS) is a modeling and simulation formalism that has been widely used to study the dynamics of discrete event systems. Cell-DEVS is a DEVS-based formalism that defines spatial models as a cell space assembled of a group of DEVS models connected together. CD++ is a modeling and simulation toolkit capable of executing DEVS and Cell-DEVS models that has proven to be useful for executing complex models. We present the design and implementation of a distributed simulation engine, known as D-CD++, which exposes CD++ simulation utilities as machine-consumable services. In addition, we present the design and implementation of the Web-Service components which enable D-CD++ to expose the simulation functionalities to remote users. Enabling CD++ with Web-Services technology provides a solid framework for interoperating different DEVS implementations in order to achieve a standard DEVS Modeling Language and simulation protocols. This paves the road towards DEVS standardization, while providing a mashup approach, which can lead to higher degree of reuse and reduced time to set up and run experiments, and making sharing among remote users more effective. To prove this fact, we integrate it within larger services (such as a 3D visualization engine), showing the mechanism to incorporate to other environments (including geographical information systems, web-based applications and other modeling and simulation tools) through using standard Web-Service tools. Performance of D-CD++, major bottlenecks and communication overheads are analyzed.     

基于DEVS/CD++的抢险救灾物资保障仿真建模研究

突发自然灾害条件下的抢险救灾行动是典型的离散事件系统,在分析离散事件系统规范(DEVS)模型描述的基础上,构建了抢险救灾物资保障DEVS仿真模型,分析了仿真实体,设计了仿真流程,给出了耦合模型和主要原子模型结构。并在CD++中对该模型进行了仿真试验,得到了较为合理的仿真结果,为开展抢险救灾应急保障模拟训练奠定了基础。     

A software framework for fine grain parallelization of cellular models with OpenMP: Application to fire spread

We are dealing here with the parallelization of fire spreading simulations following detailed physical experiments. The proposal presented in this paper has been tested and evaluated in collaboration with physicists to meet their requirements in terms of both performance and precision. For this purpose, an object-oriented framework using two abstraction levels has been developed. A first level considers the simulation as a global phenomenon which evolves in space and time. A local level describes the phenomena occurring on elementary parts of the domain. In order to develop an extensible and modular architecture, the cellular automata paradigm, the DEVS discrete event system formalism and design patterns have been used. Simulation treatments are limited to a set of active elements to improve execution times. A new kind of model, called Active-DEVS is then specified. The model is computed with a fine grain parallelization very efficient for present day multi-core processors which are elementary units of modern computing clusters and computing grids. In this paper, the parallelization with Open MultiProcessing (OpenMP) standard directives on Symmetric MultiProcessing (SMP) architectures is discussed and the efficiency of the retained solution is studied.     

A location-based fog computing optimization of energy management in smart buildings: DEVS modeling and design of connected objects

Nowadays, smart buildings rely on Internet of things (IoT) technology derived from the cloud and fog computing paradigms to coordinate and collaborate between connected objects. Fog is characterized by low latency with a wider spread and geographically distributed nodes to support mobility, real-time interaction, and location-based services. To provide optimum quality of user life in modern buildings, we rely on a holistic Framework, designed in a way that decreases latency and improves energy saving and services efficiency with different capabilities. Discrete EVent system Specification (DEVS) is a formalism used to describe simulation models in a modular way. In this work, the sub-models of connected objects in the building are accurately and independently designed, and after installing them together, we easily get an integrated model which is subject to the fog computing Framework. Simulation results show that this new approach significantly, improves energy efficiency of buildings and reduces latency. Additionally, with DEVS, we can easily add or remove sub-models to or from the overall model, allowing us to continually improve our designs.     

Self-reproducible DEVS formalism

System reproduction model to the growing system structure can be used to design modeling formalisms for variable system architectures having historical characteristics. We introduce a discrete event system specifications (DEVS)-based extended formalism that a system structure gradually grows through self-reproductions of system components. The proposed formalism is applied to atomic DEVS modeling and coupled DEVS modeling. As extended-atomic DEVS model, atomic self-reproduction (SR) DEVS modeling to a system component makes virtual-child atomic DEVS models. By SR DEVS modeling, a child coupled model can be also reproduced from a parent coupled model. When a system component model reproduces its system component, a child component model can receive its parent model characteristics including determined role or behavior, and include different structure model characteristics. A virtual-child model that has its parent characteristics can also reproduce next child model which may show similar attributes of the grand-parent model.