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Web services are gaining high popularity and importance on mobile devices. Connected to ad-hoc networks, they provide the possibility to establish spontaneously even complex service-based workflows and architectures. However, usually these architectures are only as stable and reliable as the underlying network infrastructure. Since topologies of mobile ad-hoc networks behave unpredictably, dependability within them can be only achieved with a dynamic replication mechanism. In this paper we present a highly flexible solution for replication and synchronization of stateful Web services and discuss the behavior of the implemented prototype in large-scale simulations.  相似文献
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网格服务与静态资源不同,是有状态的,能够随时间和网格用户的调用不断的改变自身状态。为了能够消除州格服务的访问瓶颈、实现对网格服务的就近访问和网格服务的负载均衡,必须能够实现对有状态的网格服务进行复制。而网格服务的复制需要对许多不同的动态改变的资源进行复制,即对网格服务运行所需的硬件环境进行搭建、软件环境进行复潮,本文就有状态网格服务结构与复制方法进行了探讨。  相似文献
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In this paper, we design the Real-Time Fault-Tolerant Object Group (RFTOG) model that supports the grouping of distributed objects that are required for distributed application. The proposed model basically provides two services. One is the group management service, which supports both consistency maintenance and transparency of the replicated objects with a variety of replication mechanisms. It also provides the load balancing of distributed applications. The other is real-time service in an object group. When the clients request the service to the service object selected through the load balance, this service guarantees the service execution within deadline for the clients’ requests. We develop the Naval Air Defense System (NADS) simulator for verifying the effectiveness of the services proposed by the RFTOG model.  相似文献
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Replicating web services over physically distributed servers can offer client applications a number of QoS benefits, including higher availability and reduced response time. However, selecting the “best” service replica to invoke at the client-side is not a trivial task, as this requires taking into account factors such as local and external network conditions, and the servers’ current workload. This paper presents an empirical assessment of five representative client-side service selection policies for accessing replicated web services. The assessment measured the response time obtained with each of the five policies, at two different client configurations, when accessing a world-wide replicated service with four replicas located in three continents. The assessment’s results were analyzed both quantitatively and qualitatively. In essence, the results show that, in addition to the QoS levels provided by the external network and the remote servers, characteristics of the local client environment can have a significant impact on the performance of some of the policies investigated. In this regard, the paper presents a set of guidelines to help application developers in identifying a server selection policy that best suits a particular service replication scenario.  相似文献
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针对传统容错方法在融合网络环境下服务组合的低效性,本文提出了一种快速可靠的服务组合容错方法.该方法首先采用模糊逻辑,对服务的临时性故障进行服务重试;然后采用多属性决策理论,对服务的永久性故障进行服务复制;最后通过改进的粒子群算法,对永久性故障进行服务补偿.基于真实数据集的实验结果表明,所提方法在故障排除率、故障处理时间与组合最优度方面,均优于其它方法.  相似文献
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杨娜  刘靖 《计算机科学》2017,44(7):61-67, 97
云计算环境下,失效成为一种常态行为,可靠性保障能力不足不仅成为云计算应用推广的主要障碍,而且还促使云计算环境下的容错服务研究成为一个亟待解决的问题。针对目前云计算容错服务研究中存在的用户容错需求定义无法直接反映用户关心的可靠性问题,以及云容错服务供应商资源得不到灵活利用等问题,提出了一种融合容错需求和资源约束的云容错服务适配方法。从用户的角度,以组件为单位,基于可靠性对用户的容错需求进行定义。从云容错服务供应商的角度,分别在其资源充足和资源不足的情况下研究最佳的容错服务适配方法,并使用最优化理论求解该适配方法下的容错服务。实验结果表明,所提出的容错服务适配方法生成的容错服务能更好地满足用户和云容错服务供应商的需求。  相似文献
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In this paper, we propose a simulation model to study real‐world replication workflows for cloud storage systems. With this model, we present three new methods to maximize the storage space usage during replica creation, and two novel QoS aware greedy algorithms for replica placement optimization. By using a simulation method, our algorithms are evaluated, through a comparison with the existing placement algorithms, to show that (i) a more evenly distributed replicas for a data set can be achieved by using round‐robin methods in replica creation phase and (ii) the two proposed greedy algorithms, named GS_QoS and GS_QoS_C1, not only have more economical results than those from Chen et al., but also guarantee the QoS for clients. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献
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