QCWS: an implementation of QoS-capable multimedia web services

QoS (Quality of Service), which defines service quality such as latency, availability, timeliness and reliability, is important for web applications that provide real-time information, multimedia content, or time-critical services. Many web applications are best implemented by servers with a guaranteed server processing capacity. In this research, we study the QoS control issues using the current Web services standards. We propose a QoS-capable Web service architecture, QCWS, by deploying a QoS broker between Web service clients and providers. The functions of the QoS broker module include tracking QoS information about servers, making selection decisions for clients, and negotiating with servers to get QoS agreements. We have implemented a QCWS prototype using IBM WSDK, enhanced with simple QoS capabilities. We have measured the performance running under different service priorities.     

WC-Stress:基于QoS的Web集群服务器性能评价工具

针对当前Web通用服务器性能评测工具并不能满足Web集群系统性能评测的需要,该文的研发重点在于构造一个高性能的支持QoS的Web集群服务器评测工具WC-Stress(WebClusterStress)。它的特点包括:可组装的组件结构;支持Web集群的评测需要:如区分服务;支持细粒度的QoS性能评测:如资源优化调度算法的支持;支持新的Web访问特征:如自相似请求的产生。最后给出了此评测工具对笔者设计的一种新型Web集群服务器的测试结果。     

Quality-of-service oriented web service composition algorithm and planning architecture

In the next few decades, it is expected that web services will proliferate, many web services will offer the same services, and the clients will demand more value added and informative services rather than those offered by single, isolated web services. As the result, the problem of synthesizing web services of high quality will be raised as a prominent issue. The clients will face the trouble of choosing or creating composition plans, among numerous possible plans, that satisfy their quality-of-service (QoS) requirements. Typical QoS properties associated with a web service are the execution cost and time, availability, successful execution rate, reputation, and usage frequency. In engineering perspective, generating the composition plan that fulfills a client’s QoS requirement is a time-consuming optimization problem. To resolve the problem in a timely manner, we propose a constraint satisfaction based web service composition algorithm that combines tabu search and simulated annealing meta-heuristics. As an implementation framework of the algorithm, we suggest a QoS-oriented web service composition planning architecture. The architecture maintains expert made composition schemas in a service category and assists the client as pure user to choose the one he/she wants to use. The main modules of the architecture are composition broker and execution plan optimizer. With the aid of the UDDI server, the composition broker discovers candidate outsourced web services for each atomic process of the selected schema and gathers QoS information on the web services. After that, the execution plan optimizer runs the web service composition algorithm in order to generate a QoS-oriented composition plan. The performance of the algorithm was tested in a simulated environment.     

Functionality Aware Dynamic Composition of Web Services

The composition of the web service is a common technique to attain the best results of complex web tasks. The selection of appropriate web services, linking those services in the action flow and attaining the actual functionality of the task are the important factors to be considered. Even though different frameworks and methods have been proposed to dynamically compose web services, each method has its advantage and disadvantage over the other. Most of the methods give much importance to the Quality of Service (QoS) but fail to achieve the actual functionality after composition. This paper proposes a functionality-oriented composition technique for composing web services. Moreover, this method helps reach the extreme functionality of each web service in the composition towards customer satisfaction. Apart from considering the overall QoS of every single service, the non-functional parameters associated with these services are also considered for achieving the expected functionality. Each of these non-functional parameters has a vital role in the functional performance of the web service. The web services that satisfy the non-functional requirements are chosen to form the composition to attain the best performance. The list of services in the proposed composition method is different from the conventional one, which is composed based on the overall QoS. The non-functional parametric values, the QoS of each web service and the overall QoS after composition are evaluated for the proposed method and experimentally analyzed to prove their advantage over the others.     

一种基于客户地址的QoS Web服务器的设计与实现

设计并实现了一种基于客户地址的ＱｏＳ Ｗｅｂ服务器,它能对客户的服务请求设定不同的服务等级,并按不同的服务策略响应客户的服务请求。实验结果表明,ＱｏＳ Ｗｅｂ服务器能够有效地实现了期望的ＱｏＳ服务。     

一种支持QoS约束的Web服务发现模型

服务质量(QoS)描述了一个产品或服务满足消费者需求的能力．提供有保证的QoS是Web服务在商业应用中获得成功的关键．如何动态地选择出最适合用户需求的Web服务正在引起研究领域的关注．该文提出了一种支持QoS约束的Web服务发现模型(WSDM-Q)．该模型定义了一组描述Web服务QoS及信誉度的分类tModel,引入了QoS量化的概念,采用了QoS协商和反馈机制,支持携带QoS描述信息的服务发布和基于QoS约束的服务发现．协商机制允许服务提供者根据运行时的状态对服务请求进行接纳控制,反馈机制允许服务注册中心对服务提供QoS的信誉度进行动态评估和调整。该模型不需要改变UDDI的内部实现,能够直接在现有的UDDI服务上进行扩展．作者已经基于Mierosoft.Netf平台和Microsoft UDDI服务实现了一个原型系统．     

Hybrid Metaheuristics Web Service Composition Model for QoS Aware Services

Recent advancements in cloud computing (CC) technologies signified that several distinct web services are presently developed and exist at the cloud data centre. Currently, web service composition gains maximum attention among researchers due to its significance in real-time applications. Quality of Service (QoS) aware service composition concerned regarding the election of candidate services with the maximization of the whole QoS. But these models have failed to handle the uncertainties of QoS. The resulting QoS of composite service identified by the clients become unstable and subject to risks of failing composition by end-users. On the other hand, trip planning is an essential technique in supporting digital map services. It aims to determine a set of location based services (LBS) which cover all client intended activities quantified in the query. But the available web service composition solutions do not consider the complicated spatio-temporal features. For resolving this issue, this study develops a new hybridization of the firefly optimization algorithm with fuzzy logic based web service composition model (F3L-WSCM) in a cloud environment for location awareness. The presented F3L-WSCM model involves a discovery module which enables the client to provide a query related to trip planning such as flight booking, hotels, car rentals, etc. At the next stage, the firefly algorithm is applied to generate composition plans to minimize the number of composition plans. Followed by, the fuzzy subtractive clustering (FSC) will select the best composition plan from the available composite plans. Besides, the presented F3L-WSCM model involves four input QoS parameters namely service cost, service availability, service response time, and user rating. An extensive experimental analysis takes place on CloudSim tool and exhibit the superior performance of the presented F3L-WSCM model in terms of accuracy, execution time, and efficiency.     

A negotiation‐based service selection approach using swarm intelligence and kernel density estimation

Nowadays, the cloud computing environment is becoming a natural choice to deploy and provide Web services that meet user needs. However, many services provide the same functionality and high quality of service (QoS) but different self‐adaptive behaviors. In this case, providers' adaptation policies are useful to select services with high QoS and high quality of adaptation (QoA). Existing approaches do not take into account providers' adaptation policies in order to select services with high reputation and high reaction to changes, which is important for the composition of self‐adaptive Web services. In order to actively participate to compositions, candidate services must negotiate their self‐* capabilities. Moreover, they must evaluate the participation constraints against their capabilities specified in terms of QoS and adaptation policies. This paper exploits a variant of particle swarm optimization and kernel density estimation in the selection of service compositions and the concurrent negotiations of their QoS and QoA capabilities. Selection and negotiation processes are held between intelligent agents, which adopt swarm intelligence techniques for achieving optimal selection and optimal agreement on providers' offers. To resolve unknown autonomic behavior of candidate services, we deal with the lack of such information by predicting the real QoA capabilities of a service through the kernel density estimation technique. Experiments show that our solution is efficient in comparison with several state‐of‐the‐art selection approaches.     

一种基于Web Service的分级QoS的研究与实现

随着Web Service技术的广泛应用,Qos成为一个非常重要的问题．以服务响应时间为Qos参数,验证了一种基于Web Service的分级QoS方法,提出了目标时间预设模型,并针对优化问题提出一种基于动态规划的解决方法,并实现了原型系统．实验数据表明这种方法有效地控制了负载平衡,实现了服务分级．     

基于QoS和多级索引的Web服务发布订阅

发布订阅机制有利于实现对大规模Web服务的主动管理,提出了基于QoS的Web服务发布订阅模型和系统架构,设计了基于QoS和多级索引的Web服务匹配算法。Web服务的QoS属性和订阅的属性约束所形成相应的匹配关系构成模型的关键;将发布的Web服务及其QoS和服务订阅一起生成过滤矩阵,通过属性约束覆盖可以减少重复匹配;按QoS属性类型对发布的Web服务建立多级索引,生成属性到服务的映射,可以实现服务订阅的快速匹配。实验结果表明,该Web服务发布订阅系统比传统方法有较大提升,能够适应于大规模分布式Web服务管理。     

RDRP: Reward-Driven Request Prioritization for e-Commerce web sites

Meeting client Quality-of-Service (QoS) expectations proves to be a difficult task for the providers of e-Commerce services, especially when web servers experience overload conditions, which cause increased response times and request rejections, leading to user frustration, lowered usage of the service and reduced revenues. In this paper, we propose a server-side request scheduling mechanism that addresses these problems. Our Reward-Driven Request Prioritization (RDRP) algorithm gives higher execution priority to client web sessions that are likely to bring more service profit (or any other application-specific reward). The method works by predicting future session structure by comparing its requests seen so far with aggregated information about recent client behavior, and using these predictions to preferentially allocate web server resources. Our experiments using the TPC-W benchmark application with an implementation of the RDRP techniques in the JBoss web application server show that RDRP can significantly boost profit attained by the service, while providing better QoS to clients that bring more profit.     

一种基于杂草优化的全局Web服务选择算法

随着网络中的Web服务数量的暴增,基于QoS的服务选择成为保证组合服务质量和可靠性的关键环节。针对当前服务选择算法全局优化能力弱的问题,将服务选择建模为带约束的非线性最优化问题,并提出一种基于杂草优化的服务选择算法。首先随机产生一组服务选择可行解并将其编码为杂草个体,进而根据个体的QoS效用值确定个体的繁殖数,最后以高斯分布方式指导种群的扩散完成对解空间的快速搜索。理论分析与实验结果表明,该算法有效性和鲁棒性强,可获得相较于已有文献更优的全局解。     

基于信誉的语义Web服务发现

服务发现在语义Web领域是一个挑战性问题.一个关键问题是发现满足用户功能需求的最佳服务.同样重要的是,电子商务应用还要求发现满足QoS需求的最佳服务.由此提出一个基于信誉管理的分布式服务选择框架.它主要有以下特点：用一个结构化的覆盖网络作为分布式服务存储系统来提高系统的有效性和可扩展性; 提出一个QoS感知的语义Web服务发现方法,并给出基于用户反馈的分布式信誉度评估算法.最后用一个例子示范算法如何解决实际问题.     

Web QoS控制研究综述

Internet的服务模式正由传统的数据通信与信息浏览向电子交易与服务转变 ,Web服务器系统作为支持电子商务的核心设施 ,需要对不同的用户或HTTP请求提供区分服务和性能保证 ,因此必须具备建立和支持服务质量 (QualityofService ,QoS)控制的机制与策略 .该文综述了WebQoS控制的研究现状 ,包括Web请求的分类机制、Web服务器应用软件的QoS控制机制、操作系统的WebQoS控制机制、中间件的WebQoS控制机制以及Web服务器集群系统的QoS控制机制与策略 ,并分析了进一步的研究方向 .     

基于Agent的Web服务集成模型与集成算法

针对现有Web服务集成方法在动态性、灵活性和智能性等方面存在的不足,提出一种基于Agent的Web服务集成模型,对模型中多Agent系统的组织结构和交互方式进行了设计。为实现集成服务整体的QoS目标,以一个通用的Web服务QoS度量模型为基础,将局部最优与全局最优的思想相结合,提出一种基于QoS的Web服务集成路径选择算法,通过实验验证了其有效性。     

The Virtual Service Grid: an architecture for delivering high‐end network services

This paper presents the design of a new system architecture, Virtual Service Grid (VSG), for delivering high‐performance network services. The VSG is based on the concept of the virtual service which provides location, replication, and fault transparency to clients accessing remotely deployed high‐end services. One of the novel features of the virtual service is the ability to self‐scale in response to client demand. The VSG exploits network and service information to make adaptive dynamic replica selection, creation, and deletion decisions. We describe the VSG architecture, middleware, and replica management policies. We have deployed the VSG on a wide‐area Internet testbed to evaluate its performance. The results indicate that the VSG can deliver efficient performance for a wide range of client workloads, both in terms of reduced response time and in the utilization of system resources. Copyright © 2002 John Wiley & Sons, Ltd.     

一个面向语义服务发现的QoS本体

随着网络上服务数量的急剧增长,用户使用服务有了更多的选择。服务的QoS属性是用户实施服务选择的一个重要准则。为了实现支持QoS的语义服务匹配和服务选择,本文对语义QoS规范进行了深入研究,并根据QoS和应用的相关性提出了一种分层的QoS语义模型。该模型使得服务提供者可以基于SLA在不同的场景下为用户提供不同层次的QoS保障。在此模型基础上,本文对支持QoS的语义服务匹配与服务选择算法进行了详细讨论。此外,还给出了一个基于QoS本体的服务发现框架。     

动态选择Web服务的QoS本体设计

QoS信息是动态选择Web服务的重要依据.本体描述可以使Web服务成为机器可读、可理解和可操作的实体,从而可实现Web服务的自动组合.分析了Web服务的各种Qos参数,设计了一个分层的OWL描述QoS本体结构,分别表示Web服务不同方面的QoS信息,并根据Agent的思想给出了一个Web服务的改进结构,这样Web服务的使用者可利用它们动态选择最合适的Web服务.     

一种考虑QoS数据可信性的服务选择方法

随着Internet上功能相似的Web服务的逐渐增多,在运行时刻基于服务质量(QoS)对Web服务进行查找和选择已成为研究热点.现有的基于QoS的服务选择方法通常假定服务提供者和使用者给出的QoS数据都是真实可信的,然而这一假设在实际中往往很难保证.为此,提出了一种考虑QoS数据可信性的服务选择方法.方法从QoS数据来源的角度对质量属性进行分类和计算:对于数据来自服务提供者的质量属性,使用以往运行数据统计,对提供者的QoS数据进行修正;对于数据来自服务使用者的质量属性,通过计算用户间以往反馈的相似程度权衡不同QoS反馈数据的可信程度.对此给出了实现框架,并通过一组模拟实验说明该方法能够有效地削弱不可信的QoS数据对服务选择的影响,增强了Web服务选择结果的准确性.     

基于QoS的Web服务选择方法研究新进展*

随着服务计算、云计算技术的迅速发展,具有相同或相似功能但服务质量（QoS）不同的可用服务已大规模部署在互联网上。如何从这些海量Web服务中为服务组合选择令人满意的服务成了一个重要的研究问题,其选择方法是影响组合服务的QoS 和服务组合性能高低的关键因素。为了解决该问题,研究者们已开发了许多服务选择方法以帮助用户选择合适的服务。针对近五年基于QoS的Web服务选择方法的新进展进行了综述。归纳了包括运用Skyline计算、协同过滤、优化算法、多属性决策支持理论和混合方法等一些典型的服务选择方法,讨论了各方法的优势和局限性,并根据当前研究现状,探讨了该领域的发展趋势和未来研究方向和挑战。