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．     

A high performance backoff protocol for fast execution of composite web services

Using web services to expose applications over the Internet is now a widely accepted practice. Currently, there are several ongoing efforts that provide ways to effectively compose web services distributed across different organizations. One of the problems underlying the deployment of such composite services on the web, however, is service co-allocation that arises when a composite service needs to ensure all the required component services to be available for execution at the same time. Motivated by this, this paper presents a new decentralized protocol, named web service co-allocation protocol (WSCP), which can facilitate fast execution of composite web services. The proposed framework is an enhancement of the famous two phase commit protocol through the incorporation of tentative hold phase as well as the employment of a new high performance backoff protocol developed to better address the dynamics of the service co-allocation problem. The simulation results show that the proposed approach yields significant improvements over existing protocols.     

基于工作流技术的复合语义Web服务框架

随着Internet和Web应用的快速发展,Web应用模式及Web服务的异构和分散问题日益突出,如何复合繁复而庞大的Web服务群成了一项繁杂的工作。该文描述了一个复合语义Web服务框架的设计和实现过程。利用本体模型及工作流技术,该Web服务框架能够动态复合基本Web服务并在动态Web环境下自动执行,提高了Web应用的灵活性,并结合语义Web和工作流理论在提供智能化Web服务方面作了一次新的尝试。     

一种基于分布式哈希表的Web服务目录系统

分析了集中式UDDI注册中心存在的缺点。结合P2P技术，基于分布式哈希表提供的高效的数据定位功能，提出了一种分布式Web服务目录系统，讨论了该系统下Web服务的发布与发现过程以及目录系统的维护。在该服务目录系统中，服务的描述信息分布在各个节点上，能够克服集中式UDDI注册中心的缺陷。     

Semantic web service composition testbed

A huge amount of web services are deployed on the Web, nowadays. These services can be used to fulfill online requests. Requests are getting more and more complicated over time. So, there exists a lot of frequent request that cannot be fulfilled using just one web service. For using web services, composing individual services to create the added-value composite web service to fulfill the user request is necessary in most cases. Web services can be composed manually but it is a too tedious and time consuming task. The ability of automatic web service composition to create a new composite web service is one of the key enabling features for the future for the semantic web. There are some successful methods for automatic web service composition, but the lack of standard, open, and lightweight test environment makes the comparison and evaluation of these composition methods impossible. In this paper we propose an architecture for a light weight and scalable testbed to execute, test and evaluate automatic web service composition algorithms. The architecture provides mandatory components for implementing and evaluation of automatic web service composition algorithms. Also, this architecture provides some extension mechanisms to extend its default functionalities. We have also given reference implementations for web service matchmaking and composition. Also, some scenarios for testing and evaluating the testbed are given. We have found that the performance of the composition method will dramatically decrease as the number of web services increases.     

Context-based matching for Web service composition

In this paper, we propose a novel matching framework for Web service composition. The framework combines the concepts of Web service, context, and ontology. We adopt a broad definition of context for Web services, encompassing all information needed for enabling interactions between clients and providers. Context-based matching for Web services requires dealing with three major research thrusts: context categorization, modeling, and matching. We first propose an ontology-based categorization of contextual information in Web service environments. We then define a two-level mechanism for modeling Web service contexts. In the first level, service providers create context specifications using category-specific Web service languages and standards. In the second level, context specifications are enveloped by policies (called context policies) using WS-Policy standard. Finally, we present a peer-to-peer architecture for matching context policies. The architecture relies on a context matching engine, context policy assistants, and context community services. Community services implement rule-based techniques for comparing context policies. Recommended by: Zakaria Maamar     

A Novel Intermediary Framework for Dynamic Edge Service Composition

Multimedia content,user mobility and heterogeneous client devices require novel systems that are able to support ubiquitous access to the Web resources.In this scenario,solutions that combine flexibility,efficiency and scalability in offering edge services for ubiquitous access are needed.We propose an original intermediary framework,namely Scalable Intermediary Software Infrastructure (SISI),which is able to dynamically compose edge services on the basis of user preferences and device characteristics.The SISI framework exploits a per-user profiling mechanism,where each user can initially set his/her personal preferences through a simple Web interface,and the system is then able to compose at run-time the necessary components.The basic framework can be enriched through new edge services that can be easily implemented through a programming model based on APIs and internal functions.Our experiments demonstrate that flexibility and edge service composition do not affect the system performance.We show that this framework is able to chain multiple edge services and to guarantee stable performance.     

基于服务组合的可信软件动态演化机制

以基于服务组合的可信软件为研究对象,重点研究通过组合服务的动态演化机制保障网络化软件的可信性.首先,提出了一个合理性保持的演化操作集,避免复杂的验证过程,使得演化后的组合服务保持结构合理性;在此基础上,通过构造冗余路径的方式给出了一个面向可用性保障的组合服务演化方法;然后,针对组合服务动态演化过程中运行实例的处理,设计了一个组合服务演化中运行实例在线迁移算法,为正确实施演化提供支持;最后,设计实现了一个支持动态演化的组合服务执行引擎,并通过实验验证了所提出方法的有效性.     

Peer-to-peer service provisioning in cloud computing environments

This paper aims to advance the management and delivery of services in large, heterogeneous, uncertain, and evolving cloud computing environments. The goal is important because such systems are becoming increasingly popular, yet existing service management methods do not scale well, and nor do they perform well under highly unpredictable conditions. If these problems can be solved, then Information Technology (IT) services can be made to operate in more scalable and reliable manner. In this paper, we present a peer-to-peer approach for managing services in large scale, dynamic, and evolving cloud computing environments. The system components such as virtualized services, computing servers, storage, and databases self-organize themselves using a peer-to-peer networking overlay. Inter-networking system components through peer-to-peer routing and information dissemination structure is essential to avoid the problems of management bottleneck and single point of failure that is predominantly associated with traditional centralized and hierarchical distributed (grids/clouds) system design approaches. We have validated our approach by conducting a set of rigorous performance evaluation study using the Amazon EC2 cloud computing environment. The results prove that managing services based on peer-to-peer routing and information dissemination structure is feasible and offers significant performance benefits as regards to overall system reliability, scalability, and self-management.     

一种支持服务关联的Web服务选择方法

目前存在的大多数基于QoS(quality of service)的Web服务选择方案都忽略了服务之间的关联关系, 认为服务之间是相互独立的, 使得组合服务的结果与实际有所偏差。为了提高组合Web服务QoS的精确性, 考虑到服务之间的关联关系对组合服务质量的影响, 分别对服务之间的接口关联、业务关联和统计关联三种关联关系进行研究, 提出了一种基于关联度的关联服务集合发现方法, 将支持服务关联的选择问题转换为混合整数规划模型进行求解。实验结果表明, 考虑服务之间的关联关系会提高组合Web服务的质量。     

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Petri网的语义Web服务自动组合方法

Web服务组合使得开发人员可以快速地创建自己的应用程序.但是,随着Internet上可用的Web服务数目的增加,Web服务组合是一项高度复杂的任务.针对语义Web服务的自动组合问题,提出了一种既考虑服务输入/输出又考虑服务行为约束的自动组合方法.首先,注册服务被转化为一组Horn子句形规则,用户的输入和输出请求分别被转化为Horn子句中的事实和目标,从而将寻找满足用户输入/输出请求的合成服务问题转化为Horn子句的逻辑推理问题;然后,用Petri网来为该Horn子句集建模,T-不变量技术被用来判定是否存在满足用户输入/输出请求的合成服务;最后给出了两种算法来获取既满足用户输入/输出请求又满足用户行为约束的合成服务的Petri网模型.     

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。     

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.     

An efficient composition of Web services with active network support

Composition of Web services enables collaboration among autonomous business organisations such that they can integrate their services to perform collaborative business activities. It facilitates the development of new services using pre-existing Web services thus reducing development and operational costs. However, the highly distributed, dynamic, and autonomous nature of component Web services gives rise to various issues such as service matchmaking, reliability, availability, security and efficiency. This paper presents a new protocol in order to improve the efficiency of Web services composition. The proposed protocol is based on the peer-to-peer paradigm which exploits the capabilities of underlying networks such that part of the processing is carried out at the network nodes. Efficiency of the proposed protocol is tested through various experiments. Experimental results show that the proposed protocol significantly improves performance by reducing the system response time in the composition of Web services.     

Web服务的模型检测技术探讨

从模型检测的基本概念出发,针对目前面向服务计算模式中,组合Web服务验证确认过程存在的问题,着重讨论了模型检测应用于Web服务验证中的关键技术,例如如何验证动态绑定服务的可信性,如何克服服务组合过程中的复杂性和不确定性;比较全面地总结并比较了几种具有代表性的对Web服务进行验证和确认的模型检测技术和相关工具;并探讨了应用于Web服务验证框架的模型检测技术研究中存在的一些问题及相应的解决方案.     

一种面向语义Web的组合服务演化方法研究

为了敏捷、有效地调整动态环境下的组合服务,系统地提出一种面向语义Web的组合服务结构化演化方法EM4CS。 EM4CS方法采用OWL-S语言描述的组合式语义Web服务为研究对象,将组合服务演化过程划分为3个部分、6个阶段,分别从演化需求获取、演化需求形式化表示、语法一致性维护、语义一致性维护、演化结果确认和演化结果发布与传播6个方面覆盖组合服务演化周期。EM4CS方法从系统工程的角度分析组合服务演化过程,以迭代求精的方式逐步实现演化需求,同时维持服务描述语法和语义的一致性。介绍了遵循EM4CS方法的组合服务演化支撑系统ESS4CS,该系统能够全程辅助知识工程师完成组合服务演化工作,能有效地提高组合服务演化的效率和精度。     

一个基于Petri网的Web服务组合模型

作为企业应用集成的重要手段，Web服务组合需要建立可靠的表达和分析方法。因此，基于Petri网技术定义一个Web服务组合模型，将组合Web服务的要索映射到Petri网结构。利用Petri网提供的分析技术，辅助复杂业务流程的建模，并分析验证其正确性和性能。     

一种语义Web服务调用代理的模型与实现

Web Service是最新的程序间协作交互技术,当前的Web Service应用开发过程中,程序员需要预先知道某个服务的接口细节,并写入应用程序中,这样的紧耦合降低了不同服务之间的互换性,该文提出了一种使用语义Web和Agent技术在客户端发现和调度Web Service的系统模型,并通过原型系统的演示说明其灵活性。     

A probabilistic approach to modeling and estimating the QoS of web-services-based workflows

Web services promise to become a key enabling technology for B2B e-commerce. One of the most-touted features of Web services is their capability to recursively construct a Web service as a workflow of other existing Web services. The quality of service (QoS) of Web-services-based workflows may be an essential determinant when selecting constituent Web services and determining the service-level agreement with users. To make such a selection possible, it is essential to estimate the QoS of a WS workflow based on the QoSs of its constituent WSs. In the context of WS workflow, this estimation can be made by a method called QoS aggregation. While most of the existing work on QoS aggregation treats the QoS as a deterministic value, we argue that due to some uncertainty related to a WS, it is more realistic to model its QoS as a random variable, and estimate the QoS of a WS workflow probabilistically. In this paper, we identify a set of QoS metrics in the context of WS workflows, and propose a unified probabilistic model for describing QoS values of a broader spectrum of atomic and composite Web services. Emulation data are used to demonstrate the efficiency and accuracy of the proposed approach.