时间Petri网等效变换的工作流评价

时间性能分析是工作流模型分析和评价的重要方面.首先介绍了业务过程的一般Petri网模型,然后引入时间Petri网建立工作流网的时间约束模型.提出了保持网时间约束特性不变的网变换规则和时间性能计算方法,对工作流网进行化简及时间性能计算,并给出了相应的算法.最后通过一个实例说明本方法的应用过程.     

基于Matlab环境的Petri网的仿真方法

该文介绍了佩特利网(Petri网)和Statefow的基本概念，给出Petri网在Matlab环境下的仿真方法．并以单水箱系统的混合Petri网模型为例进行说明，结合仿真结果对Peri网的性能进行了初步分析。     

时间约束工作流的可调度性分析

提出一种时间约束工作流的可调度性分析方法。针对时间约束Petri网（Timing Constraint Petri Nets,TCPN）为普通Petri网无法建模多参与资源的不足,给出了扩展的时间约束Petri网（w-TCPN）的定义;结合w-TCPN的拓扑结构,从模型和实例两个层次,给出了w-TCPN变迁可调度的判定定理;提出了时间约束的调整策略。w-TCPN的研究使得时间约束工作流的建模和可调度性分析更加合理。     

利用时间约束Petri网进行项目绩效分析

时间Petri网(Time Petri Net)以及时延Petri网(Timed Petri Net)通过将时间约束引入到变迁中,广泛运用于任务调度以及性能分析,但是对于项目绩效分析所要求的关键路径、最短工期、成本分析等问题却无法有效解决.提出一种新的时间约束Petri网:将时间约束引入到库所中,在全局时钟的基础上,同时赋予Petri网的库所以延迟时间域和持续时间域两种时间约束,并且为T→P流关系的权函数赋予有色资源属性.给出时间约束Petri网的形式化定义,定义了变迁的发生规则,并引入状态类来计算状态的成本空间,给出状态类的计算方法.最后结合一个实例说明了利用时间约束Petri网进行项目的绩效分析的可行性.并用双色甘特图对时间约束Petri网的可达标识进行表述.     

基于Petri网的IRBAC 2000域间动态转换SMER约束违反检测

Kapadia等人提出的IRBAC2000模型是在基于角色的访问控制(role-based access control,RBAC)模型基础上,通过角色互联和动态角色转换实现管理域间的互操作.职责分离是RBAC模型3个基本安全原则之一,而IRBAC2000模型没有考虑静态职责分离可能会造成域中静态互斥角色约束违反问题.在相关研究基础上分析了该问题,提出一种新颖的基于Petri网模型的分析方法,该方法相比以前文献中的方法简单、直观.给出了根据IRBAC2000模型构造对应Petri网的算法,基于该图形化模型可直观表示IRBAC2000模型,分析和给出了IRBAC2000违反静态互斥角色(static mutual exclusive roles,SMER)约束的充分必要条件和检测算法,通过一个实例分析验证了其有效性与正确性.为了在进行角色关联和用户/角色分配操作时不会违反SMER约束,也基于Petri网分析讨论了执行两种管理操作保证安全的先决条件,为IRBAC2000模型的安全性提供了安全保证机制.     

时间约束Petri网的可调度性分析研究

1 引言时间约束Petri网(Timing Constraint PetriNets,TCPN’s)是具有广义时间约束的Petri网,它综合了时间Petri网)(Time Petri Nets)和赋时Petri网(Timed Petri Nets)的共同特点,具有经典Petri网的理论基础和额外的时间约束能力。在实时系统建模中,它可对其它与时间有关的Petri网所不能描述的冲突结构进行建模和分析。TCPN’s使用弱触发规则,即:使能的变迁可触发也可不触发,完全由调度者决     

Petri网的进程表达式与语言表达式

Petri网的语言和进程都是网系统行为的一种有效的描述手段,对应的进程表达式和语言表达式给出了系统全体行为的约束描述．本文首先对Petrl网的进程表达式进行了类型的划分并给出了相应的代数判定依据，随后证明了Petri网的进程表达式与语言表达式的类型一致性，由此给出了由进程表达式求取语言表达式的算法，为基于Petri网语言(尤其是无界Petri网)分析实际的物理系统提供了更为有效的途径．     

基于约束优化的Petri网可达性分析

Petri网的可达性判定问题是进行Petri网分析的基础。通过分析目前求解Petri网可达问题的判定方法和基于约束程序的Petri网可达问题判定方法,提出一种基于约束优化的Petri网可达问题判定方法,该方法是在状态方程法的基础上,利用约束程序寻求可行解,再利用优化求最优解,从而减少问题搜索的分支,达到减少状态方程的解空间的目的。最后通过实例的求解验证算法能够提高判定效率。     

PETRI网与ISO传输协议的形式描述

本文介绍了用Petri网描述协议的方法,给出了ISO传输层第三类协议的Petri网说明,并且利用可达树、可达图等分析工具对所给Petri网进行了分析,然后讨论了所给的结果。描述协议的Petri网不仅可以对协议进行验证说明,而且可以作为协议实现的一种工具。     

用UML与Petri网为智能代理建模

统一建模型语言（UML）已经成为软件系统的分析与设计的标准工具，但由它扩充而成的代理统一建模型语言（AUML）还没变成一个标准，目前的AUML规格说明还有很多的局限性，还不能胜任多代理系统的开发．Petri网是仿真、验证软件系统执行的正确性与有效性的形式化工具．本文主要分析当前AUML规格说明和Petri网概念．找出它们之间的结合点，提出用Petri网扩充AUML的方法．将其应用于多代理系统的开发，就能实施之前运用Petri网进行系统的正确性与有效性验证．     

Access-control language for multidomain environments

The XML role-based access control (X-RBAC) specification language addresses multidomain environments' policy-specification needs. X-RBAC is based on an extension of the widely accepted US National Institute of Standards and Technology role-based access-control (RBAC) model. In addition to allowing specification of RBAC policies and facilitating specification of timing constraints on roles and access requirements, X-RBAC provides a framework for specifying mediation policies in a multidomain environment where RBAC policies have been employed.     

Security analysis of GTRBAC and its variants using model checking

Security analysis is a formal verification technique to ascertain certain desirable guarantees on the access control policy specification. Given a set of access control policies, a general safety requirement in such a system is to determine whether a desirable property is satisfied in all the reachable states. Such an analysis calls for the use of formal verification techniques. While formal analysis on traditional Role Based Access Control (RBAC) has been done to some extent, recent extensions to RBAC lack such an analysis. In this paper, we consider the temporal RBAC extensions and propose a formal technique using timed automata to perform security analysis by analyzing both safety and liveness properties. Using safety properties one ensures that something bad never happens while liveness properties show that some good state is also achieved. GTRBAC is a well accepted generalized temporal RBAC model which can handle a wide range of temporal constraints while specifying different access control policies. Analysis of such a model involves a process of mapping a GTRBAC based system into a state transition system. Different reduction rules are proposed to simplify the modeling process depending upon the constraints supported by the system. The effect of different constraints on the modeling process is also studied.     

Control Synthesis of Petri Nets Based on S-Decreases

A method for constructing a controller for a discrete event system modeled by a Petri net is presented in this paper. The control specification of the system is given by a set of linear inequality constraints defined on the marking of the net. The controller that forces the net to obey the constraints is an extended Petri net, which is synthesized based on minimal support S-decreases. The method can deal with general Petri nets with uncontrollable transitions, and then provides a systematic way for synthesizing net-based controllers for discrete event systems.     

基于Time Petri Net的实时系统冲撞检测与消解

time Petri net(TPN)在实时控制系统的建模中得到广泛应用,而冲撞是Petri网及其扩展模型的重要行为,解决冲撞是正确分析模型动态行为的关键.由于引入时间约束,使得TPN模型的使能和触发语义比Petri网模型的语义复杂,冲撞的检测及消解变得更加困难.首先根据时间约束,给出了变迁持续使能时延迟区间的计算方法,并证明了该方法的正确性;然后在此基础上定义并证明了TPN模型中冲撞的检测方法;给出了冲撞时间区间及修改时间约束的冲撞消解方法;最后通过实例验证说明了该方法的有效性和正确性.     

Timing constraint Petri nets and their application toschedulability analysis of real-time system specifications

We present timing constraint Petri nets (or TCPN's for short) and describe how to use them to model a real-time system specification and determine whether the specification is schedulable with respect to imposed timing constraints. The strength of TCPN's over other time-related Petri nets is in the modeling and analysis of conflict structures. Schedulability analysis is conducted in three steps: specification modeling, reachability simulation, and timing analysis. First, we model a real-time system by transforming its system specification along with its imposed timing constraints into a TCPN; we call this net N_s. Then we simulate the reachability of N_s to verify whether a marking, M_n, is reachable from an initial marking, M_o. It is important to note that a reachable marking in Petri nets is not necessarily reachable in TCPN's due to the imposed timing constraints, Therefore, in the timing analysis step, a reachable marking M_n, found in the reachability simulation step is analyzed to verify whether M_n, is reachable with the timing constraints. M_n is said to be reachable in the TCPN's if and only if we can find at least one firing sequence σ so that all transitions in σ are strongly schedulable with respect to M_o under the timing constraints. If such M_n can be found, then we can assert that the specification is schedulable under the imposed timing constraints, otherwise the system specification needs to be modified or the timing constraints need to be relaxed. We also present a synthesis method for determining the best approximation of the earliest fire beginning time (EFBT) and the latest fire ending time (LFET) of each strongly schedulable transition     

时间Petri网的ECS-class可达性分析方法

时间Petri网(TPNs)是实时系统时间特性常用的描述和验证的Petri网模型,可达性分析是Petri网模型最基本分析方法.基于"状态类(State-class)"的可达性分析方法不能正确计算并发情况下的时间延迟,而基于"带时间戳的状态类(CS-class)"的可达性分析方法不能正确处理冲突情况下的事件调度,因此提出了"扩展的带时间戳的状态类(ECS-class)"可达性分析方法.它不仅正确的计算时间延迟,而且合理地调度事件.并对一个时间Petri网模型进行可达性分析验证.     

Modeling and analysis of the behavior of information systems

Many widely used specification techniques for information systems are based on a hierarchy of information flow diagrams. A method is introduced which preserves the benefits of these techniques and adds the precision of the Petri net formalism. Information-flow diagram hierarchies are formalized by notions of net theory. The bottom-level nets of a hierarchy are treated as Petri nets. The behavior model of the information system is the Petri net derived by repeatedly replacing each part of a net by its associated refinement. As a prerequisite for such replacements, the data abstractions relation information flows of different level are specified by a semantic hierarchy data model. The nets in the hierarchy are appended by dynamic counterparts of the abstractions so that a consistent replacement becomes possible. The interface behavior of the nets in the hierarchy is analyzed, using the concept of behavior constraints as a formal measure of correct interface behavior. The behavior model can be derived in an iterative bottom-up way by first analyzing a net for fulfillment of its associated behavior constraint and afterward integrating it into the next-higher-level net     

Network-centric control based on Petri nets in the structured discrete-event system

Using the concepts of network-centric control, we develop a design methodology for a controlling Petri net in real-time automation systems. The methodology involves the structured discrete-event system (SDES) model to analyze the functionality and coherence of the object. We define structure of the model, as well as propose a technique for analyzing and modeling the object via the process Petri net. Finally, we suggest an analysis technique for the process Petri net and develop a design method for a supervisor, i.e., a controlling Petri net which implements the SDES specification (in coherence with the process net).     

Generalized stochastic Petri nets: a definition at the net leveland its implications

The class of Petri nets obtained by eliminating timing from generalized stochastic Petri net (GSPN) models while preserving the qualitative behavior is identified. Structural results for those nets are derived, obtaining the first structural analysis of Petri nets with priority and inhibitor arcs. A revision of the GSPN definition based on the structural properties of the models is presented. It is shown that for a (wide) class of nets, the definition of firing probabilities of conflicting immediate transitions does not require the information on reachable markings. Identification of the class of models for which the net-level specification is possible is also based on the structural analysis results. The procedure for the model specification is illustrated by means of an example. It is also shown that a net-level specification of the model associated with efficient structural analysis techniques can have a substantial impact on model analysis     

基于可达标识列计时Petri网的时态特征及可控性研究

应用时态逻辑提出计量Ｐｅｔｒｉ网的形式化分析方法,基于可达标识列研究受控系统的时态特征及其可控性与控制不变性,给出控制逻辑存在的充要条件,提出了时态公式分解方法,并讨论了禁止状态避免问题。