单件小批量产品生产进度延迟事件的petri网仿真

由于个性化需求的发展,多品种、单件小批量已逐渐成为主流生产方式,这类产品因为制造工艺复杂、涉及的制造单位很多,或者有的产品可能会边生产边改进,因此在生产过程中常常会出现意外情况导致生产进度不能按时完成。设计了进度延迟petri网模型(Production Schedule Delay Petri Net,PSDPN),当某工序的实际生产进度发生延迟时,基于PSDPN模型对后面加工工序进行推理仿真,来推理后面哪些加工工序的进度受到了影响,仿真结果帮助提醒生产管理人员对相关工序进行赶工来保证产品在交货期之前顺利完成。

延迟时间Petri网的验证分析

延迟时间Petri网(Delay Time Petri Nets,DTPN)是一类重要的时间扩展Petri网系统,解决了其他时间扩展Petri网(如时间Petri网)在保存时间约束时所面临的困难。可调度验证的目的是验证工作流模型时间约束的合理性,对流程实例的时间可达性进行仿真。提出一种基于DTPN的时间约束工作流验证分析方法。给出了DTPN的相关定义,并结合工作流控制结构描述了变迁可触发的时间条件;提出了DTPN触发点的概念以及基于此的验证分析算法;简要分析了DTPN的特性。DTPN的研究丰富完善了现有时间Petri网体系,具有积极的意义。

基于延迟时间Petri网的工作流相似性度量方法

为了解决实时系统中流程相似性的判定问题,提出一种基于流程中活动的拓扑结构和触发点的流程相似性度量方法。采用延迟时间Petri网(Delay Time Petri Nets,DTPN)模型来表示流程,用于找出流程的触发调度;定义活动时间约束路由关系,给出它们之间的距离和相似度计算公式,进而计算出流程之间的相似度;在此基础上设计相关算法,并且分析时间复杂度。通过实例验证了该算法在时间约束工作流相似性度量方面的有效性。

基于Petri网下哲学家就餐问题模型的改进与推广

哲学家就餐问题是描述在共享资源下同步与并发的经典案例,活性与无饥饿性是求解此问题的前提,效率是基本要求。基于两个许可卡的传递策略,已经给出了无饥饿解的Petri网模型,并且在该模型基础上的改进解决了许可卡的传递问题同时也解决了拥有许可卡且准备就餐的两位相邻哲学家之间共享资源的冲突问题。然而以上改进并没有真正实现效率上的高效且不易推广到哲学家人数大于5位的情形。

Performance Evaluation of Service Orchestration with Dynarric Latency Simulation

Dynamic latency over the Intemet is an Important parameter for evaluating the performance of Web service orchestration. In this paper, we propose a performance analyzing and correctness checking method for service orchestration with dynamic latency simulated in Colored PetriNets （CPNs）. First, we extend the CPN to Web Service Composition Orchestration Network System （WS-CONS） for the description of dynamic latency in service orchestration. Secondly, with simulated dynamic latency, a buffer-limited policy and admittance-control policy are designed in WS- CONS and implemented on CPN Tools. In the buffer-limited policy, the passing messages would be discarded if the node capacity is not adequate. In the admittance-control policy, the ability of a message entering the system depends on the number of messages concurrently flowing in the system. This helps to enhance the success rate of message passing. Finally, the system performance is evaluated through running models in CPN Tools. Simulated results show that the dynamic latency plays an important role in the system throughput and response latency. This simulation helps system designers to quickly make proper compromises at low cost.

Performance Analysis of Integrative QoS Scheme for Routers

This paper proposes an integrative scheme of DiffServ （differentiated service） for the IP-based network. In the scheme, QoS （Quality of Service） is ranked according to the level of both the queuing delay and the drop precedence that base on the relative differentiated service; it does not take the resource reservation problem into consideration for making its implementation more simple and flexible. We will propose an implemented architecture including edge routers and core routers, and the PHB （per-hop-behavior） architecture of the routers is generalized. We adopt ERED （extended random early discard） mechanism for drop precedence and use proportional delay differentiation for queuing delay. In the proportional delay differentiation topic, we propose a new WTP （waiting time priority）-like algorithm. Besides, a new stochastic petri net model of the PHB model is given, and the performance of whole implemented PHB architecture is analyzed, too.