On optimal decision for QoS-aware composite service selection

The increasing popularity of employing web services for distributed systems contributes to the significance of service discovery. However, duplicated and similar functional features existing among services require service consumers to include additional aspects to evaluate the services. Generally, the service consumers would have different view on the quality of service (QoS) of service attributes. How to select the best composite service in theory among available service (WS) candidates for consumers is an interesting practical issue. This work proposes a QoS-aware service selection model based on fuzzy linear programming (FLP) technologies, in order to identify their dissimilarity on service alternatives, assist service consumers in selecting most suitable services with consideration of their expectations and preferences. This approach can obtain the optimal solution of consensual weight of QoS attribute and fuzzy positive ideal solution (FPIS) by extending LINMAP method, developed by Srinivasan and Shocker. Finally, two numerical examples are given to demonstrate the process of QoS-aware web service selection. The experimental results demonstrated that it is a feasible and supplementary manner in selecting the of web services.     

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.     

QoS-aware web service selection with negative selection algorithm

Web service selection, as an important part of web service composition, has direct influence on the quality of composite service. Many works have been carried out to find the efficient algorithms for quality of service (QoS)-aware service selection problem in recent years. In this paper, a negative selection immune algorithm (NSA) is proposed, and as far as we know, this is the first time that NSA is introduced into web service selection problem. Domain terms and operations of NSA are firstly redefined in this paper aiming at QoS-aware service selection problem. NSA is then constructed to demonstrate how to use negative selection principle to solve this question. Thirdly, an inconsistent analysis between local exploitation and global planning is presented, through which a local alteration of a composite service scheme can transfer to the global exploration correctly. It is a general adjusting method and independent to algorithms. Finally, extensive experimental results illustrate that NSA, especially for NSA with consistency weights adjusting strategy (NSA+), significantly outperforms particle swarm optimization and clonal selection algorithm for QoS-aware service selection problem. The superiority of NSA+ over others is more and more evident with the increase of component tasks and related candidate services.     

A novel QoS model and computation framework in web service selection

With the rapid development of e-commerce over Internet, web services have attracted much attention in recent years. Nowadays, enterprises are able to outsource their internal business processes as services and make them accessible via the Web. Then they can dynamically combine individual services to provide new value-added services. With the increasing number of web services having equivalent functionality, the binding procedure is driven by some non-functional, Quality of Service (QoS) criteria, such as the money cost, response time, reputation, reliability or a trade-off between them. Thus, an important problem is, given QoS constraints, how to aggregate and leverage individual service??s QoS information to derive the optimal QoS of the composite service. In this paper, we propose a novel QoS model for performing flexible service selection. The key idea of the model is to relax users?? QoS constraints and try to find the most possible services satisfying users?? QoS requirements. Based on the proposed QoS framework, we develop various algorithms for making service selection on individual and composite services. We also introduce a top-k ranking strategy to reflect a user??s personalized requirements. Experimental evaluation shows the proposed QoS model is efficient and practical.     

QoS-driven metaheuristic service composition schemes: a comprehensive overview

Services Oriented Architecture provides Web Services (WSs) as reusable software components that can be applied to create more complicate composite services for users according to the specified QoS limitations. However, considering many WSs that may be appropriate for each task of a user-submitted workflow, finding the optimal WSs for a composite WS to maximize the overall QoS is an NP-hard problem. As a result, numerous composition schemes have been suggested in the literature to untangle this problem by using various metaheuristic algorithms. This paper presents a comprehensive survey and taxonomy of such QoS-oriented metaheuristic WS composition schemes provided in the literature. It investigates how metaheuristic algorithms are adapted for the WS composition problem and highlight their main features, advantages, and limitations. Also, in each category of the studied composition schemes, a comparison of their applied QoS factors, evaluated metrics, exploited simulators, and properties of the applied metaheuristic algorithms are explained. Finally, the concluding remarks and future research directions are summarized to help researchers in working in this area.

     

Probabilistic approach for QoS-aware recommender system for trustworthy web service selection

We present a QoS-aware recommender approach based on probabilistic models to assist the selection of web services in open, distributed, and service-oriented environments. This approach allows consumers to maintain a trust model for each service provider they interact with, leading to the prediction of the most trustworthy service a consumer can interact with among a plethora of similar services. In this paper, we associate the trust in a service to its performance denoted by QoS ratings instigated by the amalgamation of various QoS metrics. Since the quality of a service is contingent, which renders its trustworthiness uncertain, we adopt a probabilistic approach for the prediction of the quality of a service based on the evaluation of past experiences (ratings) of each of its consumers. We represent the QoS ratings of services using different statistical distributions, namely multinomial Dirichlet, multinomial generalized Dirichlet, and multinomial Beta-Liouville. We leverage various machine learning techniques to compute the probabilities of each web service to belong to different quality classes. For instance, we use the Bayesian inference method to estimate the parameters of the aforementioned distributions, which presents a multidimensional probabilistic embodiment of the quality of the corresponding web services. We also employ a Bayesian network classifier with a Beta-Liouville prior to enable the classification of the QoS of composite services given the QoS of its constituents. We extend our approach to function in an online setting using the Voting EM algorithm that enables the estimation of the probabilities of the QoS after each interaction with a web service. Our experimental results demonstrate the effectiveness of the proposed approaches in modeling, classifying and incrementally learning the QoS ratings.     

Broker-based SLA-aware composite service provisioning

QoS-aware service composition aims to satisfy users’ quality of services (QoS) needs during service composition. Traditional methods simply attempt to maximize user satisfaction by provisioning the composite service instance with the best QoS. These “best-effort” methods fail to take into account that there also exist other consumers competing for the service resources and their decisions of service selection/composition can impact on QoS. Since user's QoS needs can be met once the demanded level is reached, in this paper, we propose an “on-demand” strategy for QoS-aware service composition to replace the traditional “best-effort” strategy. The service broker is introduced to facilitate implementation of this strategy: it first purchases a number of service instances for each component from providers and then provisions the composite services with different QoS classes to consumers. This paper focuses on how the broker follows the service level agreement (SLA) to provision composite services in the “on-demand” manner. This problem is formally expressed as the minimization of the QoS distance function between SLA and QoS of composite service instances, under a series of constraints. Heuristic approaches are proposed for the problem and experiments are conducted at last to verify their effectiveness and efficiency.     

QoS需求驱动的服务配置框架

为支持服务质量敏感的基于组件的分布式应用的开发,中间件需要为组件提供并配置各种服务质量服务的非功能性属性.目前的组件架构提供的服务配置方式大多是静态的,且没有考虑不同客户的需求.在对EJB架构进行研究的基础上,提出一种服务质量需求驱动的服务配置框架.研究了根据客户的服务质量需求,在组件实例级别自动生成服务配置决策并实施,实现对不同客户服务差分处理.框架是一个基于服务配置的决策模型,通过多选择背包问题生成服务配置策略.最后通过一个应用实例对框架进行了验证.     

Architectural reliability analysis of framework-intensive applications: A web service case study

A novel methodology for modeling the reliability and performance of web services (WSs) is presented. To present the methodology, an experimental environment is developed in house, where WSs are treated as atomic entities but the underlying middleware is partitioned into layers. WSs are deployed in JBoss AS. Web service requests are generated to a remote middleware on which JBoss runs, and important performance parameters under various configurations are collected. In addition, a modularized simulation model in Petri net is developed from the architecture of the middleware and run-time behavior of the WSs. The results show that (1) the simulation model provides for measuring the performance and reliability of WSs under different loads and conditions that may be of great interest to WS designers and the professionals involved; (2) configuration parameters have substantial impact on the overall performance; (3) the simulation model provides a basis for aggregating the modules (layers), nullifying modules, or to include additional aspects of the WS architecture; and (4) the model is beneficial to predict the performance of WSs for those cases that are difficult to replicate in a field study.     

基于不确定服务质量感知的云服务组合方法

针对不确定服务质量（QoS）感知的云服务组合优化问题的求解,提出一种不定长时间序列（ULST）模型和锦标赛策略的改进遗传算法（T-GA）。首先,基于用户对服务不同时间段的访问规律,将服务质量的长期变化构建为不定长时间序列模型,该模型能够准确地描述一段时间内用户对服务的真实QoS访问记录。其次,提出一种基于不确定QoS模型的改进遗传算法,该算法采用锦标赛选择策略代替基本遗传算法中的轮盘赌选择策略。最后,在真实数据上进行了大量实验,所提的不定长时间序列模型能够有效地解决不确定QoS感知云服务组合问题,而锦标赛策略的改进遗传算法在寻优结果和稳定性方面均优于基于精英选择策略的遗传算法（E-GA）算法,且运行速度提高近1倍,是可行、高效且稳定的算法。     

A novel heuristic algorithm for QoS-aware end-to-end service composition

Many works have been carried out to find the efficient algorithms for QoS-aware service composition in recent years. Nevertheless, on one hand, some of these works only consider the local QoS attributes in Web services composition; on the other hand, some ideas derived from QoS selection algorithms for network routing are directly applied in service composition without any adaption. A service composition model with end-to-end QoS constraints has been presented in this paper. An improved heuristics HCE based on the observation of characteristic of end-to-end service composition is proposed as a novel solution. Simulation results reveal the better performance of proposed heuristic compared to the other two heuristics, HMCOP and generic CE algorithm.     

基于QoS的网格计算经济模型

提出了基于经济模型的网格QoS控制机制,刻画了基于经济模型的网格QoS管理结构。用生产一消费模型给出基于多QoS指标的全局QoS优化模型,用整数规划中的背包问题形式化描述了以用户QoS效用函数为导向的资源分配问题。这种形式化描述将用户的QoS需求、资源稀缺以及服务成本等网格关键因素统一在一个框架中分析,提出用价格和契约来控制网格QoS的策略。     

Investigating the problems faced by older adults and people with disabilities in online environments

Irresponsible and inaccessible web design causes unnecessary problems to certain website users. By applying the web content accessibility guidelines to a website the amount of possible users who can successfully view the content of that site will increase especially for those who are in the disabled and older adult categories of online users. We present the results of assessing the compliance of a selection of websites with guidelines set out by the Web Accessibility Initiative (WAI). It was found that most sites evaluated were inaccessible to those with disabilities. Only one of the selected sites passed all three priority levels set out by the WAI. In many cases, minor modifications to sites will make them accessible to people with disabilities. Therefore it can only be speculated that the reasons for lack of conformance may vary from lack of awareness of the issue, time constraints or the general stress of having to keep up with new technologies. Companies who overlook users with disabilities however may be doing so at long-term risk to their legal position, public image and ultimately business success.     

Investigating the problems faced by older adults and people with disabilities in online environments

Irresponsible and inaccessible web design causes unnecessary problems to certain website users. By applying the web content accessibility guidelines to a website the amount of possible users who can successfully view the content of that site will increase especially for those who are in the disabled and older adult categories of online users. We present the results of assessing the compliance of a selection of websites with guidelines set out by the Web Accessibility Initiative (WAI). It was found that most sites evaluated were inaccessible to those with disabilities. Only one of the selected sites passed all three priority levels set out by the WAI. In many cases, minor modifications to sites will make them accessible to people with disabilities. Therefore it can only be speculated that the reasons for lack of conformance may vary from lack of awareness of the issue, time constraints or the general stress of having to keep up with new technologies. Companies who overlook users with disabilities however may be doing so at long-term risk to their legal position, public image and ultimately business success.     

基于树型二重结构编码遗传算法的服务选择

提出了Web服务语法业务流程树的概念,并结合基于QoS的Web服务全局选择的特点,研究了一种用于组合服务QoS优化的基于树型二重结构编码的遗传算法GATD。该方法建立在服务语法业务流程树先序遍历序列编码的基础上,采用二重编码方法处理用户的QoS约束条件,不仅能够有效地选择出满足用户QoS需求的服务资源,而且可以较好地支持服务运行时快速再规划。     

A reputation assessment model for trustful service recommendation

Nowadays, software systems are mainly Web front-based, Cloud-deployed and accessible by a wide audience over the Internet. These online systems commonly rely on Service-oriented Architecture principles, where they are built as orchestrations of RESTful (and in some rare cases as SOAP-based) services. Integrating new services in an existing orchestration is a challenging and risky task because trustworthiness of these services is not guaranteed throughout their lifetime. Reputation of services is a good indicator about the overall quality of services, because it reflects consumer satisfaction regarding the service-offered functionality and quality. Thus, reputation of services could be considered in the selection and recommendation of trustworthy services. In this paper, we present a framework for the management of web service reputation to conduct a better service recommendation. We present a reputation assessment model that aggregates fair user feedback ratings. The model includes a mechanism that prevents the introduction of malicious feedback ratings, by penalizing detected specious users. In addition, this framework includes a bootstrapping technique for estimating reputation of newcomer services based on neighbor similarity and initial advertised QoS. A set of experiments has been conducted to evaluate the effectiveness of the proposed framework. The results of these experiments highlighted the potential of our framework. These are presented at the end of the paper.     

动态Web服务合成中的服务选择算法研究

为了提高服务合成效率并更好的适应动态变化的应用环境,提出了基于流程修改的服务合成方案,使得复合服务的执行与服务发现过程并行化。提出了基于QoS属性的服务选择算法,该算法能够实现服务执行时选择服务,在考虑综合QoS信息及时间因素的基础上,通过不断更新用户需求来进行服务选择,提高了服务合成效率。实验结果表明,该选择算法可以获得满足用户需求且最优的服务,很好的保证了服务的可靠执行。     

A framework for QoS-aware binding and re-binding of composite web services

QoS-aware dynamic binding of composite services provides the capability of binding each service invocation in a composition to a service chosen among a set of functionally equivalent ones to achieve a QoS goal, for example minimizing the response time while limiting the price under a maximum value.This paper proposes a QoS-aware binding approach based on Genetic Algorithms. The approach includes a feature for early run-time re-binding whenever the actual QoS deviates from initial estimates, or when a service is not available. The approach has been implemented in a framework and empirically assessed through two different service compositions.