基于对象Petri网的离散事件系统建模仿真环境(OPMSE)

首先论述了Ｐｅｔｒｉ网和高级Ｐｅｔｒｉ网发展状况,提出了一种高级Ｐｅｔｒｉ网,即对象Ｐｅｔｒｉ网。然后介绍了基于对象Ｐｅｔｒｉ网的离散事件系统建模仿真环境ＯＰＭＳＥ。文中详细介绍了ＯＰＭＳＥ的特点与组成,并对ＯＰＭＳＥ的核心－对象Ｐｅｔｒｉ网（ＯＰＮ）的语法描述进行了重点介绍。     

离散事件系统的协调反馈控制

本文探讨以Ｐｅｔｒｉ网为模型的离散事件系统（ＤＥＳ）的某种禁止状态避免问题，提出了以Ｐｅｔｒｉ网Ｎ为基网，设计具有外部输入位置Ｐｅｔｒｉ网（ＰＮＩＰ），对Ｎ进行协调反馈控制的方法。由Ｎ现行状态反馈决定的ＰＮＩＰ的控制状态，既保证Ｎ避免禁止状态，又使Ｎ具有最大自由度。     

基于Petri网的离散事件仿真算法

本文介绍了一种基于Ｐｅｔｒｉ网的模型描述语言ＥＰＤＬ，并给出了Ｐｅｔｒｉ网与离散事件系统仿真相结合的算法。     

离散事件动态系统的代数模型及其控制器的分析计算

本文在离散事件动态系统的Ｐｅｔｒｉ网图形描述的基础上建立了相应的代数模型，该模型可以用来计算无竞争无回路Ｐｅｔｒｉ网的“最大状态”；该“最大状态”的计算在本文给出的动态反馈控制器中得到了应用。     

实时并发离散事件系统的监控

用受控赋时Ｐｅｔｒｉ网为具有并发事件的实时离散事件系统建模，并研究了这类模型下的监控问题，给出了实现给定并发事件语言的监控器存在的充要条件和一种动态监控方法。     

基于CSPN的图视化离散事件系统模拟支持环境

在离散事件模拟领域中存在着大量的模拟软件，但由于它们所采用的建模方式都不够形式化，缺乏统一的，简洁的模型描述方法，从而促使人们寻找新的更具有潜力的方法。本文提出了一个新的基于ＣＳＰＮ模型的离散事件模拟支持环境ＣＳＰＳＥ，对它的思想方法，系统设计以及实现技术进行了较为系统的阐述，显示出ＣＳＰＳＥ在离散事件模拟领域的广阔前景。     

基于混合随机Petri网的一类混合系统的模型及稳定性

混合动态系统是包含离散事件系统（ＤＥＳ）和连续变量系统（ＣＶＳ）的复杂系统。讨论了一类每个离散状态包含一个连续动态系统,且离散事件具有Ｍａｒｋｏｖ链性质的随机混合系统,在提出利用混合随机Ｐｅｔｒｉ网的建模方法的基础上,给出混合均方稳定的概念、稳定性和可镇定条件,最后以一个简单的例子做子说明和仿真。     

一类区段赋时弧有色Petri网的可达性和可阻断性分析

为了描述和分析实际复杂产时系统,提出了一种新的时间限制Ｐｅｒｔｉ网模型,区段赋时弧有色Ｒｅｔｒｉ网模型。这种Ｐｅｔｒｉ网在有色Ｐｅｔｒｉ网的库所输出弧上标注以输入库所的颜色为自变量的时间区间函数,基于一种充分考虑了系统时间不确定性的激发规划,给我段赋时弧有色Ｐｅｔｒｉ网的发生元序列的时间界估计,并以此为依据,提出了基于状态类的可达性分析方法和可阻断性分析方法。     

基于Petri网的协议并行化处理模型的描述和验证

本文提出了一个ＯＳＩ／ＲＭ运输层协议并行处理模型，以适应协议的高效处理，根据模型特点，使用Ｐｅｔｒｉ网作为形式化描述工具，对该模型进行描述，分析和验证。     

一类混杂系统的混杂时态Petri网模型

本语文为一类混杂系统的建模提出了混杂时态Ｐｅｔｒｉ网（ＨＴＰＮ）模型,在该模型下,系统的微观连续行为由混杂时态Ｐｅｔｉ网变迁对应的微分方程描述,宏观行为由变迁对应的离散事件描述,同时在该模型的基础上,讨论了混杂系统的宏观及微观运行问题,并提出了佥状态轨迹的概念来描述系统的动态行为。最后给出一实例来说明模型的合理性和应用。     

Supervisor Synthesis for Real-Time Discrete Event Systems

This paper introduces a formal framework to logically analyze and control real-time discrete event systems (RTDESs). Time Petri nets are extended to controlled time Petri nets (CtlTPNs) to model the dynamics of RTDESs that can be controlled by real-time supervisors. The logical behaviors of CtlTPNs are represented by control class graphs (CCGs) which are untimed automata with timing and control information in their state transition labels. We prove that the CCG corresponding to a CtlTPN expresses completely the logical behavior of the CtlTPN. The real-time supervisor is based on a nondeterministic logical supervisor for the CCG, including the delay for control computations to ensure the supervisor is acceptable in a true real-time environment. We prove the existence of a unique maximal controllable sublanguage of a given specification language and present an algorithm to construct the sublanguage. We also prove that the real-time supervisor meets the prespecified real-time behavior and present an online control algorithm to implement real-time supervisors. The concepts and algorithms are illustrated for an example of packet reception processes in a communication network.     

A modeling strategy for hybrid systems based on event structures

This paper considers hybrid systems which are continuous/discrete-time systems interacting with a decision maker which oversees the control and structure of the continuous/discrete-time system. These two segments combine with a processor which evaluates data to produce a three-segment model of a hybrid system having sufficient flexibility to represent a broad range of real-time situations and sufficient generality to incorporate the essential aspects of other models into a single framework. In particular the paper uses a graphically expressive controlled Petri net formulation of the decision maker and any of the usual models for the continuous/discrete-time system. Interaction between the systems occurs via three types of events: continuous/discrete-time events, decision-making events, and processor events. These types of events and their composition are rigorously defined to produce event structures and event histories. These events and event histories are used for the domain of interaction functions which specify the channels of communication between the three essential segments of the hybrid system. The event-based domains allow the disassociation of these communication channels from dependence on particular kinds of models or applications. The range of the interaction functions are binary vector-valued indicating the activation/deactivation processes in the respective segments. The entire modeling strategy is motivated by applications and models found in the literature especially flexible manufacturing systems and the C-net model of a hybrid system.This work was partially supported by the National Science Foundation under Grant No. ECS-8800910.     

组合计算模型实现系统设计与仿真*

在模块化的系统设计中,适合各个模块的最佳计算模型往往不尽相同,这些计算模型包括有穷状态自动机、Petri网、离散事件和事件关系图等.为了方便设计者和提高工作效率,有必要允许对模块采用不同的计算模型,再运用组合计算模型的理论将这些模块组合成完整的模型以用于仿真和系统的自动生成.作为应用实例,通过分层组合离散事件和事件关系图,可以设计易于扩展、修改和维护的动态系统;同样的原理也可以应用于其他计算模型,从而使它们在模块化设计中发挥各自的优点.     

基于分段执行和摘要的动态程序分析*

在模块化的系统设计中,适合各个模块的最佳计算模型往往不尽相同,这些计算模型包括有穷状态自动机、Petri网、离散事件和事件关系图等。为了方便设计者和提高工作效率,有必要允许对模块采用不同的计算模型,再运用组合计算模型的理论将这些模块组合成完整的模型以用于仿真和系统的自动生成。作为应用实例,通过分层组合离散事件和事件关系图,可以设计易于扩展、修改和维护的动态系统;同样的原理也可以应用于其他计算模型,从而使它们在模块化设计中发挥各自的优点。     

Network access protocol for hard real-time communication systems

Distributed hard real-time systems are characterized by communication messages associated with timing constraints, typically in the form of deadlines. A message should be received at the destination before its deadline expires. Carrier sense multiple access with collision detection (CSMA/CD) appears to be one of the most common communication network access schemes that can be used in distributed hard real-time systems. In this paper, we propose a new real-time network access protocol which is based on the CSMA/CD scheme. The protocol classifies the messages into two classes as ‘critical’ and ‘noncritical’ messages. The messages close to their deadlines are considered to be critical. A critical message is given the right to access the network by preempting a noncritical message in transmission. Extensive simulation experiments have been conducted to evaluate the performance of the protocol. It is shown that the protocol can provide considerable improvement over the virtual time CSMA/CD protocol proposed for hard real-time communication by Zhao et al.¹.     

Integrated dynamic scheduling of hard and QoS degradable real-time tasks in multiprocessor systems

Many time-critical applications require predictable performance and tasks in these applications have deadlines to be met. For tasks with hard deadlines, a deadline miss can be catastrophic while for Quality of Service (QoS) degradable tasks (soft real-time tasks) timely approximate results of poorer quality or occasional deadline misses are acceptable. Imprecise computation and (m,k)-firm guarantee are two workload models that quantify the trade-off between schedulability and result quality. In this paper, we propose dynamic scheduling algorithms for integrated scheduling of real-time tasks, represented by these workload models, in multiprocessor systems. The algorithms aim at improving the schedulability of tasks by exploiting the properties of these models in QoS degradation. We also show how the proposed algorithms can be adapted for integrated scheduling of multimedia streams and hard real-time tasks, and demonstrate their effectiveness in quantifying QoS degradation. Through simulation, we evaluate the performance of these algorithms using the metrics – success ratio (measure of schedulability) and quality. Our simulation results show that one of the proposed algorithms, multilevel degradation algorithm, outperforms the others in terms of both the performance metrics.     

入侵事件建模研究

入侵过程由一系列入侵行为组成,每个入侵行为包含一个或多个入侵事件,这些事件间可能存在各种各样的关系。该文对入侵事件特征进行研究,从检测角度对入侵事件进行分类。定义了入侵事件,建立了入侵事件的一般模型。从时间、空间和功能方面分析了事件间的内在联系,并依据这些关系建立了入侵事件逻辑、统计和模糊模型,以描述不同的入侵行为,并举实例予以分析。     

Aperiodic task scheduling for Hard-Real-Time systems

A real-time system consists of both aperiodic and periodic tasks. Periodic tasks have regular arrival times and hard deadlines. Aperiodic tasks have irregular arrival times and either soft or hard deadlines. In this article, we present a new algorithm, the Sporadic Server algorithm, which greatly improves response times for soft deadline aperiodic tasks and can guarantee hard deadlines for both periodic and aperiodic tasks. The operation of the Sporadic Server algorithm, its performance, and schedulability analysis are discussed and compared with previously published aperiodic service algorithms.     

基于本体的监控视频语义事件探测*

为了探测视频高层复杂事件,架构了一个视频事件分析框架,采用本体和Petri网进行推理从而获取复合事件;运用视频语义本体标注算法分析低层视频语义,在高层构建一个视频事件分析本体,将低层本体映射到事件分析本体表示高层视频事件;通过本体和扩展Petri网结合的方法对监控视频中的事件进行图形化异步事件推理;最后用semantic Web rule language(SWRL)规则表示视频监控事件的探测。实验证明,提出的方法比基于模式识别的事件探测方法更加有效。     

Real-Time Performance of Sorting Algorithms

In hard real-time systems tasks must meet their deadlines under guarantee. Soft real-time tasks may miss deadlines occasionally, as long as the entire system can provide the specified quality of service.In this paper we investigate the hard and soft real-time performance of sorting algorithms and compare it to their average performance. We show in which way the adequacy of an algorithm depends on the demanded performance criterium (hard, soft, or non real-time). The results provide a guideline to select the right sorting algorithm for a given application.