An automatic subdigraph renovation plan for failure recovery of composite semantic Web services

A Web service-based system never fulfills a user＇s goal unless a failure recovery approach exists. It is inevitable that several Web services may either perish or fail before or during transactions. The completion of a composite process relies on the smooth execution of all constituent Web services. A mediator acts as an intermediary between providers and consumers to monitor the execution of these services. If a service fails, the mediator has to recover the whole composite process or else jeopardize achieving the intended goals. The atomic replacement of a perished Web service usually does not apply because the process of locating a matched Web service is unreliable. Even the system cannot depend on the replacement of the dead service with a com- posite service. In this paper, we propose an automatic renova- tion plan for failure recovery of composite semantic services based on an approach of subdigraph replacement. A replacement subdigraph is posed in lieu of an original subdigraph, which includes the failed service. The replacement is done in two separate phases, ofltine and online, to make the recovery faster. The ofitine phase foresees all possible subdigraphs, pre-calculates them, and ranks several possible replacements. The online phase compensates the unwanted effects and executes the replacement subdigraph in lieu of the original subdigraph. We have evaluated our approach during an experiment and have found that we could recover more than half of the simulated failures. These achievements show a significant improvement compared to current approaches     

Towards a formal study of automatic failure recovery in protocol-based web service composition

In the protocol-based Web service composition, the runtime unavailability of component services may result in a failed execution of the composite. In literature, multiple recovery heuristics have been proposed. This work provides a formal study and focuses on the complexity issues of the recovery problem in the protocol-based Web service composition. A recovery is a process responsible of migrating the failed execution into an alternative execution of the composite that still has the ability to reach a final state. The alternative execution is called a recovery execution. Following failure occurrence, several recovery executions may be available. The problem of finding the best recovery execution(s) is called the recovery problem. Several criteria may be used to determine the best recovery execution(s). In this work, we define the best recovery execution as the one which is attainable from the failed execution with a maximal number of invisible compensations with respect to the client. We assume that all transitions are compensatable. For a given recovery execution, we prove that the decision problem associated with computing the number of invisibly compensated transitions is NP-complete, and thus, we conclude that deciding of the best recovery execution is in \(\Sigma _2^P\).     

一种基于角色的分布式动态服务组合方法

服务组合是开放环境中实现跨组织敏捷应用集成的重要技术.许多研究采用集中的服务组合引擎管理组合服务的执行,在系统的可伸缩性、消息传输效率及自治性等方面存在局限.针对集中结构的上述问题,提出一种基于角色的分布式动态服务组合方法,通过划分组合服务的全局流程模型产生各个角色的本地流程模型,从而使得组合服务的控制逻辑及执行负载能够对等地分布到多个结点.讨论了本地流程模型的生成算法及部署与执行机制.模拟实验结果表明,与集中式结构相比,该方法能够更有效地支持大规模并发访问以及大数据量的消息转输,有助于提高组合服务的可伸缩性.     

Self-adapting workflow reconfiguration

Because web services are highly interoperable, they are capable of providing uniform access to underlying technologies, allowing developers to choose between competing services. Workflow languages, such as BPEL, compose and sequence Web service invocations resulting in meaningful, and sometimes, repeated tasks. Their prevalence means there may be multiple Web services that perform the same operation with some better than others depending on the situation. Their potential for being unavailable at critical workflow execution times forces a reliance on such redundant services. One remedy for unavailability and situational awareness constraints is using quality of service factors and user-directed preferences to assign priorities to workflows and services to perform run-time replacement. In this paper we describe a novel approach to self-adapting workflow reconfiguration. We discuss the implementation of our approach embodied by the Next-generation Workflow Toolkit that supports runtime workflow reconfiguration using BPEL with a commercial workflow engine. A key design feature is the decoupling of user-directed changes regarding service priority from the actual workflow execution, allowing NeWT to effectively manage and recover from workflow changes at any time. We evaluate NeWT by comparing the same example across multiple commercial systems that claim reconfiguration capabilities.     

基于用户视角的组合Web服务响应时间优化

针对响应时间,通过选择、调用合适的成员Web服务,对组合Web服务的QoS进行优化．该优化方法基于用户的视角,将组合Web服务运行时用户一次等待周期中需要执行的所有任务作为一个整体进行调度;同时根据组合Web服务流程的不同环节中用户对等待时间的不同敏感度,设置调度参数,降低关键环节超时的风险．实验表明,此方法可以有效地优化组合Web服务的响应时间,提高用户的满意度和QoS．     

基于代理和BPEL4WS的Web服务合成与实现

Web服务的交互和实现被推荐通过软件代理来实现.Web服务目前还不能很好地支持动态、自适应的服务组合和分布式业务流程.软件代理在建模、知识表达和交互等技术上的优势,能够强化Web服务的交互和动态应用能力.基于代理和面向流程建模的BPEL4WS,可以实现Web服务面向业务应用的合成与执行,支持多个协同的业务流程及其动态配置.系统分析了代理、BPEL4WS和Web服务整合的技术与实现方案,利用JADE平台开发了相关的测试模型,并且以网上拍卖为案例,验证了所提方案及实现.     

考虑失效恢复的组合服务性能建模与分析

互联网环境下运行的组合服务易受到资源故障和组件失效影响而导致失效.已有的失效恢复措施在提高服务可用性的同时也会对服务的性能产生负面影响.为了对失效可恢复情况下的组合服务性能进行量化,通过综合组合服务失效类型和恢复策略,给出一种考虑失效恢复的组合服务性能分析模型.采用排队Petri网(queueing Petri net,简称Qn)描述组合服务的失效发生及其恢复处理过程,重点研究实施重试和替换策略的服务运行情况.详细描述了考虑失效恢复的服务节点和链路QPN模型的内部结构,在此基础上,通过服务交互机制构建组合服务分散执行的性能模型.最后,采用QPME工具仿真和比较不同失效发生率、失效类型分布和恢复策略下组合服务模型的性能表现.结果表明,该方法能够定量分析失效恢复对组合服务性能的影响,有助于指导不确定网络环境下的信息服务系统失效恢复策略实施方案的设计.     

A simulation-based approach for dynamic process management at web service platforms

Web services technology is being adopted as a viable deployment approach for future distributed software systems that enable business-to-business and business-to-consumer interactions across the open and dynamic internet environment. Recent research is focused on developing support technologies for web service discovery, on-demand service composition, and robust execution to facilitate web services based deployment of business processes. Developing techniques to cope with the volatile and open nature of the web during execution of composite services at the service platform is essential for delivering reliable and acceptable performance in this new process delivery framework. In this paper, we propose a simulation-based framework to guide scheduling of composite service execution. Online simulation of the dynamics of the open environment is used for scheduling service requests at the service platform. Comparison of the look-ahead simulation for different scheduling policies with the current execution state provides guidelines for service execution in order to cope with system volatility. We have implemented a prototype of the proposed framework and illustrate the feasibility of our approach with experimental studies.     

Towards an ontology-based approach for specifying and securing Web services

With the increasing popularity of Web services and increasing complexity of satisfying needs of users, there has been a renewed interest in Web services composition. Composition addresses the case of a user request that cannot be satisfied by any available Web service, whereas a composite service obtained by integrating Web services might be used. Because Web services originate from different providers, their composition faces the obstacle of the context heterogeneity of Web services. An unawareness or poor consideration of this heterogeneity during Web services composition and execution result in a lack of the quality and relevancy of information that permits tracking the composition, monitoring the execution, and handling exceptions. This paper presents an ontology-based approach for context reconciliation. The approach also focuses on the security breaches that threaten the integrity of the context of Web services, and proposes appropriate means to achieve this integrity.     

A layered architecture for flexible Web service invocation

Web service composition is emerging as an interesting approach to integrate business applications and create intra‐organizational business processes. Single Web services are combined to create a complex Web service that will realize the process business logic. Once the process is created, it is executed by an orchestration engine that invokes individual Web services in the correct order. However, Web services composing the workflow sometimes become unavailable during the run‐time phase, blocking process execution. This paper describes an architecture that allows the flexible orchestration of business processes. With this approach, Web services composing the process can be automatically substituted with other compatible Web services during process execution. A methodology is defined to evaluate Web service compatibility based on interface matching, in order to select substitutable Web services. Copyright © 2005 John Wiley & Sons, Ltd.     

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.     

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.     

SLA感知的事务型组合服务容错方法

针对组合服务容错逻辑与执行逻辑不分离,以及容错过程易出现SLA（service level agreement）违反的现状,提出一种SLA感知的事务型组合服务容错方法.该方法首先采用有限状态机建模组合服务执行过程,对其状态进行监控;其次,采用监控自动机监控执行过程中的SLA属性,确保不出现SLA违反;然后,对于补偿过程,采用改进的差分进化算法快速寻找最优恢复规划;最后,该方法与组合服务执行逻辑相分离,所以易于开发、维护和更新.基于真实数据集的实验结果验证了所提方法在故障处理时间与组合最优度方面优于其他方法,并且对不同故障规模适应良好.     

On Composite Web Services Provisioning in an Environment of Fixed and Mobile Computing Resources

We present a framework for Web services provisioning in a hybrid environment of fixed and mobile computing resources. Several obstacles still hinder the seamless provisioning of Web services in mobile environments. Examples of such obstacles are: throughput and connectivity of wireless networks, limited computing resources of mobile devices, and risks of communication channel disconnections. In the proposed framework, software agents represent users, providers of services, and providers of resources. The business logic of composite services is expressed as a process model using statecharts formalism. Among other things, the use of agents provides an infrastructure that has the ability to handle disconnections during service preparation for execution. The framework also integrates a service execution planning approach to optimally select computing resources (fixed or mobile) on top of which services will be executed.     

一种基于软件Agent面向Web Services的工作平台

构造了基于软件Agent面向Web Services的工作平台（JAWS平台）。介绍了JAWS平台的设计思想和整体构成,并分析了平台中各个组成部分以及它们之间的关系,给出了平台中web Services的执行流程。在此平台中,软件Agent是一个自治的代表用户利益的实体,软件Agent独立与用户交互,查询满足用户需求的Web Services,并将其组成复合服务。在复合服务执行过程中,由软件Agent在恰当的时间逐一触发复合服务中的web Services,并监视其执行过程,控制平台的一切行为。由于采用了软件Agent技术,JAWS平台具有了自主性、智能性、开放性。     

Web Service Composition Based on QoS Rules

For workflow-based service composition approach, the relations between the Web service QoS and environments are usually not considered, so that the information about QoS for composite service selection is inaccurate. It makes the selected composite service inefficient, or even unexecutable. To address this problem, a novel service composition approach based on production QoS rules is proposed in this paper. Generally, it is very difficult to directly analyze how different kinds of environment factors influence the Web service QoS. We adopt “black-box” analysis method of optimizing composite services, discovering the knowledge such as “the QoS of one Web service will be higher in specific environments”. In our approach, the execution information of the composite service is recorded into a log first, which will be taken as the basis of the subsequent statistical analysis and data mining. Then, the timely QoS values of the Web services are estimated and the production QoS rules being used to qualitatively express the different performances of the Web service QoS in different environments are mined. At last, we employ the mined QoS knowledge of the Web services to optimize the composite service selection. Extensive experimental results show that our approach can improve the performance of selected composite services on the premise of assuring the selecting computation cost.     

一种Web服务组合的可信评估方法

软件可信性日益成为软件工程研究中的热点问题,作为软件资源主要形态的Web服务的可信性也受到了越 来越多的关注。目前对于Web服务可信性的研究主要集中在单一服务QoS属性的可信评价,而针对服务组合的可信 性研究较少。提出了一种通用的原子服务可信评佑模型,并结合原子服务在服务组合执行时的权重,给出了一种基于 结构分析的服务组合可信性的评估方法。最后,结合网络购物实例描述了服务组合可信性评估方法的实验过程。     

Runtime Monitoring CompositeWeb Services Through Stateful Aspect Extension

The execution of composite Web services with WS-BPEL relies on externally autonomous Web services. This implies the need to constantly monitor the running behavior of the involved parties. Moreover, monitoring the execution of composite Web services for particular patterns is critical to enhance the reliability of the processes. In this paper, we propose an aspect-oriented framework as a solution to provide monitoring and recovery support for composite Web services. In particular, this framework includes 1) a stateful aspect based template, where history-based pointcut specifies patterns of interest cannot be violated within a range, while advice specifies the associated recovery action; 2) a tool support for runtime monitoring and recovery based on aspect-oriented execution environment. Our experiments indicate that the proposed monitoring approach incurs minimal overhead and is efficient. This work is supported by the National Natural Science Foundation of China under Grant Nos. 60673112, 90718033, the National Basic Research 973 Program of China under Grant No. 2009CB320704, and the High-Tech Research and Development 863 Program of China under Grand Nos. 2006AA01Z19B, 2007AA010301.     

QoS-Driven Self-Healing Web Service Composition Based on Performance Prediction

Web services run in a highly dynamic environment, as a result, the QoS of which will change relatively frequently. In order to make the composite service adapt to such dynamic property of Web services, we propose a self-healing approach for web service composition. Such an approach is an integration of backing up in selection and reselecting in execution. In order to make the composite service heal itself as quickly as possible and minimize the number of reselections, a way of performance prediction is proposed in this paper. On this basis, the self-healing approach is presented including framework, the triggering algorithm of the reselection and the reliability model of the service. Experiments show that the proposed solutions have better performance in supporting the self-healing Web service composition. This work is supported by the National Natural Science Foundation of China under Grant No. 60773218.