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.     

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.     

一种基于自适应框架的Web服务选择算法

在服务组合中,动态环境的变化可能导致参与组合的Web服务行为发生变化。为此,提出基于自适应框架的Web服务选择算法,用于获取公共服务注册处的信息,并将其记录在本地绑定库中,利用链接分析算法获得绑定库某一时刻高链接度的Web服务,实现服务选择。实验结果证明,该算法可在服务组合中动态选择高质量的Web服务,降低由服务质量变化造成的服务组合失败率。     

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。     

组合Web服务访问控制策略合成研究

针对Web服务多域环境下组合服务的访问控制策略合成问题,首先提出基于属性的Web服务访问控制策略描述框架,并结合原子属性值限制的属性描述方法,对服务访问控制策略进行了形式化表达。然后,通过分析服务组合描述文档中的控制结构,并研究访问控制策略合成算子和访问控制策略规则的合成运算,提出组合Web服务访问控制策略合成方法,实现了组合服务访问控制策略的合成。最后,结合实例给出组合Web服务的访问控制策略合成流程,验证了合成方法的实用性。     

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 composite service. In this paper, we propose an automatic renovation 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, offline and online, to make the recovery faster. The offline 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.     

Dynamic and Personalized Web Services Composition in E-Business

Building composite Web services can save significant time and cost for developing new applications and enhancing the interoperability and collaboration among E-business partners. This article proposes a framework for dynamic and personalized composition of Web services using an approach that integrates not only functional attributes of Web services, but also nonfunctional attributes such as service requirements, quality of service, and the preferences and constraints of individual service consumers. A prototype system based on the proposed framework and some implementation details are also presented.     

Composing semantic Web services under constraints

Web service composition is an inevitable aspect of Web services technology, which solves complex problems by combining available basic services and ordering them to best suit the problem requirements. Automatic composition gives us flexibility of selecting best candidate services at composition time satisfying QoS requirements; this would require the user to define constraints for selecting and composing candidate Web services. In this work, a Web service composition approach is presented in which a rich set of constraints can be defined on the composite service. The output of the framework is the schedule of Web service composition in which how and when services are executed is defined. The basic properties of the proposed approach is converting Web service composition problem into a constraint satisfaction problem in order to find the best solution that meets all criteria defined by user and providing semantic compatibility and composability during composition.     

一种利用云环境实现Web服务组合容错的方法

随着Web服务迅猛发展,基于SOA的服务组合容错性研究成为了业界关注的焦点.服务组合中组件的失效,会导致整个组合执行失败,而资源不足、服务器负载过重是引发组件失效的主要原因之一.云计算作为一种新的计算泛型,其资源整合、动态分配的特点为解决传统SOA下因资源受限而引发的失效提供了新的容错思路.FTEL层将中间件技术应用到服务组合容错上,借助云环境完成服务替换,对传统SOA下较难解决的由于资源问题引起的组件失效进行了容错.     

Service Composition and Execution Plan Generation of Composite Semantic WEB Services Using Abductive Event Calculus

Web Service composition is indispensable, as a single web service cannot satisfy the complex functional requirement of a user. The two key challenges of semantic web service composition are the discovery of the most relevant atomic services from the composite semantic web services and by no means we can assure the execution of the composed atomic services in a proper order. In this work, these two challenges are addressed, and a novel architecture is proposed for atomic service discovery, composition and automatic plan generation for the proper execution of its candidate services. The proposed architecture takes the advantage of abductive event calculus that uses abductive theorem prover to generate a plan for the proper order of execution of the atomic services. The research has found that the plan generated by the proposed architecture is sound and complete.     

动态Web服务组合研究

Web服务作为一种崭新的分布式计算模型,是Web上数据和信息集成的有效机制。动态Web服务组合作为一种灵活、快速集成信息的重要方法,成为开放异构环境中复杂分布应用的新的研究热点。本文首先分析了几种Web服务描述方式并给出了动态Web服务组合定义及模式;其次,结合目前存在的一些组合平台和框架,重点分析了基于工作流和基于AI规划的动态Web服务组合原理与典型应用,并分析了其它相关的一些动态Web服务组合策略;最后提出了动态Web服务组合面临的挑战和进一步的研究方向。     

Context-Aware Web Service Composition based on AI Planning

A web service is an application that is published on the web and can be discovered and used automatically. In many cases, a web service cannot provide the capability that the user has requested. Therefore, according to the user request, it should be possible to combine various services and produce a new composite service for the user request. Context is the information that can be used to characterize the situation of an entity. In this paper, we present our context model for web service composition and implement the newly proposed framework for context-aware web service composition and show how the newly proposed framework reduces the number of failures and composition time.     

一个基于有色Petri网的自动Web服务合成模型

提出了一个基于有色Petri网的自动Web服务合成模型,为Web服务的合成提供语义支持,提高合成服务的可靠性和可维护性.该模型将服务的合成结构分成顺序、并发、选择、循环、置换5种合成结构.给出了Web服务基于有色Petri网的形式化定义.定义了一个封闭的Web服务合成算法,通过算法获得的框架能够对Web服务进行说明性的合成.定义了一个自动Web服务合成算法,通过该算法,可以对Web服务进行有人工指导的半自动合成和无人工指导的自动合成.     

基于语义Web的动态组合服务关键技术研究

随着Webservice应用的发展,大量存在的应用服务之间需要解决共享和交互。Web服务的动态组合为解决信息共享和应用协作的瓶颈问题带来了新的方案。论文通过分析原有Web服务组合的特点,提出一个基于语义的Web服务动态组合框架,并在此基础上实现了一个动态服务组合系统原型。该原型支持组合服务的即时生成,以及在动态环境中快速部署和发布。     

一种动态服务组合中的相容性模型

异构服务组合是不同应用领域间Web服务可用性和可应用性的关键点,尤其是电子商务和电子政务应用.组合设计者尝试进行完美的组合匹配但在实际中不可能找到完全相容的服务.提出一种相容性模型,确保Web服务能够正确组合,避免意想不到的运行时失效.通过一套从语法、语义和非功能属性3个层次定义的规则来进行相容性检查.同时引入相容度的概念来度量部分和完全相容,提出一种松弛相容函数将Web服务间的相容程度转化成数量值.最后通过实验来分析相容性阈值对服务成功组合率的影响.     

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.     

网格环境下动态编程模型研究

论文通过对0GSA体系结构的研究,对网格环境下的编程进行了探索,利用WebServiees对网格环境下传统的分布式软件资源进行封装,尽可能自动化地把异构的软件资源提供的服务封装为Web服务,把这些对外提供Web服务的构件组装为一个新的服务。从构件角度出发来看,这实际上也是一个复合构件,这个系统对外也以Web服务的方式提供服务。随着网格环境下服务数量的快速增长,如何自动地根据服务请求进行服务的动态组合,已成为一个迫切需要解决的问题。论文通过分析原有Web服务组合的特点,提出了基于关键字匹配的动态编程模型,根据用户需求的实时变化,方便用户编程。     

Dynamic composition and optimization of Web services

Process-based composition of Web services has recently gained significant momentum for the implementation of inter-organizational business collaborations. In this approach, individual Web services are choreographed into composite Web services whose integration logics are expressed as composition schema. In this paper, we present a goal-directed composition framework to support on-demand business processes. Composition schemas are generated incrementally by a rule inference mechanism based on a set of domain-specific business rules enriched with contextual information. In situations where multiple composition schemas can achieve the same goal, we must first select the best composition schema, wherein the best schema is selected based on the combination of its estimated execution quality and schema quality. By coupling the dynamic schema creation and quality-driven selection strategy in one single framework, we ensure that the generated composite service comply with business rules when being adapted and optimized.