Web服务组合的可靠性动态评估模型*

为了合理、高效、动态地评估Web服务组合的可靠性,为服务请求者提供高质量的组合服务,提出了一个Web服务组合的可靠性动态评估模型。该模型对服务提供者发布至UDDI注册中心的Web服务进行语义预先处理,根据语义Web服务间的逻辑组合关系,基于预推理技术构造Web服务的自动组合框架,提出了Web服务的自动组合算法,建立Web服务组合方案的路径结构;利用随机Petri网对满足服务请求者需求的服务组合路径结构进行可靠性建模,结合在线获取的Web服务可靠性信息,对Web服务组合的可靠性进行动态评估。实验示例结果分析表明,提出的模型能确保Web服务组合方案的有效性和提高服务组合的效率,对Web服务组合的可靠性评估具有较强动态性和灵活适应性。     

基于成本效益系数的Web服务组合可靠性优化方法

为了解决Web服务组合优化过程计算量大、非线性等问题,提出在给定成本约束下利用成本效益系数(CBC)对Web服务组合可靠性进行优化的方法。首先分析了Web服务组合结构模式及其对应的可靠性函数,进一步给出服务组合的可靠性计算方法,并建立非线性可靠性优化模型;然后,通过组件服务的成本及其可靠性关系计算成本效益系数,进一步确定Web服务组合的优化方案,再根据优化模型计算得到优化结果;最后,以组件服务可靠性数据为基础,通过与传统的优化方法比较,验证了基于成本效益系数的方法可以在给定成本约束时获得更高的可靠性。实验结果表明,所提方法对Web服务组合进行可靠性优化是有效、合理的。     

基于成本效益系数的Web服务组合可靠性优化方法

为了解决Web服务组合优化过程计算量大、非线性等问题,提出在给定成本约束下利用成本效益系数(CBC)对Web服务组合可靠性进行优化的方法。首先分析了Web服务组合结构模式及其对应的可靠性函数,进一步给出服务组合的可靠性计算方法,并建立非线性可靠性优化模型;然后,通过组件服务的成本及其可靠性关系计算成本效益系数,进一步确定Web服务组合的优化方案,再根据优化模型计算得到优化结果;最后,以组件服务可靠性数据为基础,通过与传统的优化方法比较,验证了基于成本效益系数的方法可以在给定成本约束时获得更高的可靠性。实验结果表明,所提方法对Web服务组合进行可靠性优化是有效、合理的。     

基于本体的Web服务可靠性模型

可靠性是Web服务选择和组合的一个重要度量标准。针对Web服务发现机制中存在效率低下和查准率不高的问题,提出了一种新的Web服务可靠性评估方法—OntoRcl。该方法基于本体技术,分析了可靠性属性的度量标准及其关系,建立了Web服务可靠性本体模型并评佑了Web服务可靠性。该方法有助于可靠性知识域的管理和开发、Web服务的可靠性评估和预测, Web服务的自动选择和组合。     

基于冗余的Web服务组合可靠性优化方法

为了确保Web服务组合的可靠性满足用户需求,该文提出一种可靠性优化方法,利用软件容错技术来提高组合服务的可靠性。在Web服务组合的可靠性预测模型的基础上,分别给出两种容错模式下可靠性优化模型的表示,对于Web服务组合的优化设计具有一定的理论指导意义。     

基于SOA的Web服务可靠性预测

在SOA架构下,服务发现的准确率是影响服务可靠性的因素之一。为了提高Web服务可靠性的预测精度,分析服务发现的失效是非常关键的。首先分析Web服务发现过程中可能出现的失效因素,构建Web服务发现的可靠性模型,并在此基础上提出新的Web服务的可靠性预测方法。最后通过实验验证了Web服务发现阶段的失效对Web服务可靠性的影响,并通过实例说明了Web服务的新的可靠性预测方法。实验结果表明,新的可靠性预测方法更加适用于Web服务。     

面向成本最小化的组合服务可靠性优化分配

在设计阶段将Web服务组合可靠性指标约束分配到各组件服务,以提供一个可靠性高、成本最小化的Web服务组合是非常必要的。为此,分析Web服务组合结构模式及其对应的可靠性。基于组件服务的可靠性和成本之间的关系函数,建立组合服务可靠性分配优化模型并利用遗传算法对其进行求解。使得在保证Web服务组合可靠性的前提下,将Web服务组合的可靠性指标合理分配给组件服务,并把成本控制到最低。实验结果表明,与其他可靠性分配方法相比,该方法在节约成本方面具有优越性,是有效且实用的,种群具有更好的收敛性。     

基于参考网的Web服务组合模型

为了确保组合Web服务执行的可靠性，提出了基于Reference nets的Web服务组合方法。精确描述了Web服务的形式化语义，使用该方法对组合Web服务控制流的八种基本结构建立模型，并给出了建模步骤。结合应用实例使用Renew2.0.1建立组合服务模型并进行仿真，进一步验证了该方法的有效性。     

基于绑定图的Web服务可靠性预测模型

为提高动态组合服务的可靠性预测精度,提出一种适用于Web动态服务的可靠性预测模型。将Web服务分解为执行路径、服务组合模块、原子服务等不同粒度的组合单位,构建各组合单位的绑定图,在绑定图的基础上按照粒度大小逐层进行可靠度预测,并将组合单位的可靠度集成为组合服务的可靠度。实例分析结果表明,与现有可靠性预测模型相比,当组合服务中服务组件的可靠度发生变化时,该模型只需计算受该服务影响的执行路径上的可靠度增量,降低了计算复杂度,并且能更高效地进行灵敏度分析以识别组合服务中的关键服务。     

一种模型驱动的WS-CDL服务组合可靠性预测方法

WS-CDL是一种主流的Web服务组合标准,描述了基于编排机制的端对端服务组件的组合方式。对基于WS-CDL的服务组合进行可靠性预测,能帮助Web服务的使用和管理者定量考察服务的可信性,并帮助他们从功能相同的服务组件中择优选取以优化整体服务流程的可靠性。然而,学术界对WS-CDL可靠性研究非常匮乏。提出了一种模型驱动的方法来预测基于WS-CDL的组合服务的可靠性。该方法首先引入一系列的转换规则,将WS-CDL中的各种活动和结构转换为等效的NMSPN网描述。在生成的NMSPN网基础上,引入了一个预测算法以分析组合服务的“流程正常结束概率”。为了对理论模型和结果进行检验,还通过WS-CDL+执行引擎对服务组合的实例进行执行并获得了流程正常结束率的实验数据。比较发现,由实验数据导出的95%置信区间完好地覆盖了理论分析结果,表明了该方法的正确性和精确性。     

OWL-S过程模型的形式化描述与相容性分析

构建组合服务的形式化模型是对其进行验证的前提与基础,然而缺乏统一的构建框架使得建模过程变得难以把握且无法实现自动化。通过对确定型有限自动机的扩展,建立了用于描述OWL-S过程模型的有限迁移系统——服务过程自动机,为组合服务的形式化建模提供了统一框架和自动化基础。同时,通过分析服务过程自动机的可接受位置及其在组合过程中可能产生的约束,将相容性划分为三个等级,从而能够在不同强度的可靠性要求下进行组合服务的验证工作。     

SRM: a staged reliability model for Web service

SOA (Service-oriented Architecture) is becoming the major architecture for building complex Web service systems. In SOA, the lifecycle of Web services consists of four stages: service publication, service discovery, service binding and service execution. Faults may occur in any stage and cause a failure of service. The reliability of services depends on not only the faults of the remote services itself, but also the faults that may occur in any SOA stage. Designing an effective and accurate reliability prediction model for Web services has become an important and necessary task. This study first proposes a staged reliability model for atomic services, which structures the reliability estimation based on the faults that may occur at each stage. Then, the reliability of composite services or service systems can be estimated based on this staged model. An experiment is conducted to study the influence of failures at each stage on the reliability of atomic services and a case study is designed to demonstrate the reliability of composite services using our staged model. In addition, the accuracy of our approach is investigated by comparing it against CBRM (component-based reliability model). Sensitivity analysis is also performed to identify critical service. Experimental results show that our staged model can obtain higher reliability prediction accuracy and is more suitable for Web services than traditional model.     

利用软件容错技术提高Web服务组合的可靠性

Web服务的一个优点就是可以通过基本服务组合形成更为复杂的服务。为了确保Web服务组合的可靠性,可以利用软件容错技术来提高服务组合的可靠性。针对BPEL流程形式描述的组合服务,本文提出了一种利用软件容错模式增强组合服务可靠性的方法,并利用随机回报网模型度量组合服务的可靠性。     

A survey of methods and approaches for reliable dynamic service compositions

An increasing amount of today’s software systems is developed by dynamically composing available atomic services to form a single service that responds to consumers’ demand. These composite services are distributed across the network, adapted dynamically during run-time, and still required to work correctly and be available on demand. The development of these kinds of modern services requires new modeling and analysis methods and techniques to enable service reliability during run-time. In this paper, we define the required phases of the composite service design and execution to achieve reliable composite service. These phases are described in the form of a framework. We perform a literature survey of existing methods and approaches for reliable composite services to find out how they match with the criteria of our framework. The contribution of the work is to reveal the current status in the research field of reliable composite service engineering.     

基于补偿业务生成图的组合服务异常处理方法研究

为提高组合Web服务执行的一致性、可靠性,提出一种基于补偿业务生成图的组合服务异常处理方法.基于业务流程中任务间补偿依赖关系,讨论了补偿业务生成图的自动生成问题.重点讨论了补偿任务、补偿目标和服务转让应用模式,并相应地介绍了支持框架和相关技术.在此基础上设计了补偿依赖关系、补偿业务生成图的自动生成及组合服务执行过程中异常处理算法.当业务流程出现异常采取向前或向后恢复处理时,该方法在保证补偿实现的同时,兼顾补偿服务不存在或补偿服务代价过高的问题,提高了业务流程执行过程中的自动化水平和自适应能力.仿真结果证实,该方法保证了异常发生时组合服务执行的可靠性和一致性.     

Survey of reliability and availability prediction methods from the viewpoint of software architecture

Many future software systems will be distributed across a network, extensively providing different kinds of services for their users. These systems must be highly reliable and provide services when required. Reliability and availability must be engineered into software from the onset of its development, and potential problems must be detected in the early stages, when it is easier and less expensive to implement modifications. The software architecture design phase is the first stage of software development in which it is possible to evaluate how well the quality requirements are being met. For this reason, a method is needed for analyzing software architecture with respect to reliability and availability. In this paper, we define a framework for comparing reliability and availability analysis methods from the viewpoint of software architecture. Our contribution is the comparison of the existing analysis methods and techniques that can be used for reliability and availability prediction at the architectural level. The objective is to discover which methods are suitable for the reliability and availability prediction of today’s complex systems, what are the shortcomings of the methods, and which research activities need to be conducted in order to overcome these identified shortcomings. The comparison reveals that none of the existing methods entirely fulfill the requirements that are defined in the framework. The comparison framework also defines the characteristics required of new reliability and availability analysis methods. Additionally, the framework is a valuable tool for selecting the best suitable method for architecture analysis. Furthermore, the framework can be extended and used for other evaluation methods as well.     

The RBAC model and implementation architecture in multi-domain environment

Nowadays in the IT convergence environment, the Service Oriented Architecture has its unique significance. The RBAC model has a variety of advantages in protecting the security of services. When the network is extended to a certain scale, it must be divided into multi domains for convenient management. However, the study to the RBAC model can be applied in multi-domain environment is still lacked. Corresponding feasible implementation architectures for the individual and composite services are also in weak. In this paper, we proposed a domain model and a domain based RBAC model can better adapt to the multi-domain security requirements. Then based on the model we designed feasible and efficient access control architectures respectively focusing on the individual services and different type of composite services. The evaluation cases showed the proposed model and implementation architectures achieved desired effects and the performances are in promising.