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.     

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/.     

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.     

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.     

Modeling discrete event scalable network systems

Scalability in simulation tools is one of the most important traits to measure performance of software. The reason is that today’s Internet is the main instance of a large-scale and highly complex system. Simulation of Internet-scale network systems has to be supported by any simulation tool. Despite this fact, many network simulators lacks support for building large models. In this work, in order to propose a new approach for scalability issue in network simulation tools, a network simulator is developed based on behavior of honeybees and high performance DEVS, modular and hierarchical system theoretic approach. A biologically-inspired discrete event modeling approach is described for studying networks’ scalability and performance traits. Since natural systems can offer important concepts for modeling network systems, key adaptive and emergent attributes of honeybees and their societal properties are incorporated into a set of simulation models that are developed using the discrete event system specification approach. Large-scale network models are simulated and evaluated to show the benefits of nature-inspired network models.     

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.     

一种基于Modelica语言的混合系统DEVS模型架构

Modelica语言采用微分方程描述系统,此外它还具备面向对象编程语言的特性,因此它不仅适用于连续系统的建模,还支持离散系统的模型架构。因此,可以将Modelica作为一种混合系统的建模语言。提出了一个Modelica语言描述的DEVS（Discrete E Vent System specification离散事件系统规范）模型架构,并通过对模型的编译过程产生C＋＋代码,获取了同时描述连续系统和离散系统建模的能力。最后给出了用Modelica语言描述的一个飞机导航控制连续一离散仿真系统的例子。     

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.     

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.     

Activity-based simulation using DEVS: increasing performance by an activity model in parallel DEVS simulation

Improving simulation performance using activity tracking has attracted attention in the modeling field in recent years. The reference to activity has been successfully used to predict and promote the simulation performance. Tracking activity, how- ever, uses only the inherent performance information contained in the models. To extend activity prediction in modeling, we propose the activity enhanced modeling with an activity meta-model at the meta-level. The meta-model provides a set of interfaces to model activity in a specific domain. The activity model transformation in subsequence is devised to deal with the simulation difference due to the heterogeneous activity model. Finally, the resource-aware simulation framework is implemented to integrate the activity models in activity-based simulation. The case study shows the improvement brought on by activity-based simulation using discrete event system specification （DEVS）.     

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.     

Modelica模型的序列化方法

Modelica是一种基于方程的陈述式建模语言,它具有面向对象、数组化表示、连续离散混合和可重用等多种特征,基于Modelica构建的模型和模型库通常规模庞大且结构复杂。编译Modelica模型的时间开销较大。本文从Modelica模型编译的角度出发,结合现有的序列化方法,提出以模型序列化来取代模型编译的部分工作,从而达到提升Modelica模型编译效率的目的。文中实现的Modelica模型序列化技术已在多领域物理系统建模与仿真平台MWorks中进行了验证与应用。     

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.     

Ptolemy离散事件模型形式化验证方法

Ptolemy是一个广泛应用于信息物理融合系统的建模和仿真工具包,主要通过仿真的方式保证所建模型的正确性.形式化方法是保证系统正确性的重要方法之一.本文提出了一种基于形式模型转换的方法来验证离散事件模型的正确性.离散事件模型根据不同事件的时间戳触发组件,时间自动机模型能够表达这个特征,因此选用Uppaal作为验证工具.首先定义了离散事件模型的形式语义,其次设计了一组从离散事件模型到时间自动机的映射规则.然后在Ptolemy环境中实现了一个插件,可以自动将离散事件模型转换为时间自动机模型,并通过调用Uppaal验证内核完成验证.最后以一个交通信号灯控制系统为例进行了成功的转换和验证,实验结果证实了该方法能够验证Ptolemy离散事件模型的正确性.     

Activity-based DEVS modeling

Use of model-driven approaches has been increasing to significantly benefit the process of building complex systems. Recently, an approach for specifying model behavior using UML activities has been devised to support the creation of DEVS models in a disciplined manner based on the model driven architecture and the UML concepts. In this paper, we further this work by grounding Activity-based DEVS modeling and developing a fully-fledged modeling engine to demonstrate applicability. We also detail the relevant aspects of the created metamodel in terms of modeling and simulation. A significant number of the artifacts of the UML 2.5 activities and actions, from the vantage point of DEVS behavioral modeling, is covered in details. Their semantics are discussed to the extent of time-accurate requirements for simulation. We characterize them in correspondence with the specification of the atomic model behavior. We demonstrate the approach with simple, yet expressive DEVS models.     

基于Modelica的多领域建模与联合仿真

为实现多领域建模仿真环境与其他仿真环境的联合仿真,提出基于Modelica多领域建模的联合仿真方案.该方案基于Modelica多领域模型的连接机制,通过Modelica模型与Simulink模块的转换机理,实现在S-Function联合仿真框架下的联合仿真.基于Modelica的多领域物理系统建模仿真工具MWorks与...     

基于笛卡尔方法的多体系统Modelica表示

针对Modelica多体建模过程较为繁琐、创建模型不够直观的问题,在研究多体系统由物理模型到数学模型再到Modelica表示的完整映射过程的基础上,采用笛卡尔方法,以多体动力学建模软件InteDyna为建模前端,在多领域物理系统建模仿真工具MWorks中实现多体系统三维可视化建模与仿真.双摆实例表明该方法有效.