A monitoring approach for runtime service discovery

Effective runtime service discovery requires identification of services based on different service characteristics such as structural, behavioural, quality, and contextual characteristics. However, current service registries guarantee services described in terms of structural and sometimes quality characteristics and, therefore, it is not always possible to assume that services in them will have all the characteristics required for effective service discovery. In this paper, we describe a monitor-based runtime service discovery framework called MoRSeD. The framework supports service discovery in both push and pull modes of query execution. The push mode of query execution is performed in parallel to the execution of a service-based system, in a proactive way. Both types of queries are specified in a query language called SerDiQueL that allows the representation of structural, behavioral, quality, and contextual conditions of services to be identified. The framework uses a monitor component to verify if behavioral and contextual conditions in the queries can be satisfied by services, based on translations of these conditions into properties represented in event calculus, and verification of the satisfiability of these properties against services. The monitor is also used to support identification that services participating in a service-based system are unavailable, and identification of changes in the behavioral and contextual characteristics of the services. A prototype implementation of the framework has been developed. The framework has been evaluated in terms of comparison of its performance when using and when not using the monitor component.     

基于服务的Agent社会组织研究

Web Service应用上的人工架构模式成为了其被高度重用的瓶颈。通过Agent对Web Service的封装能极大地改善WebService资源在应用上的主动性及智能性。针对Web Service封装后所形成的Agent服务,给出了基于服务本体及Agent服务描述语言(ASDL)的服务发现方法,并在此基础上给出了基于服务的Agent社会组织机制。实际应用证明方法可行有效。     

基于Web服务的网格体系结构及其支撑环境研究

网格技术是当前网络计算的前沿领域,基于Web服务技术构建网格系统有助于提高网格系统的可扩展性和互操作能力,是这一领域中的最新热点.但现有的工作尚未明确界定基于Web服务的网格的功能模型和实现机制.首先讨论了网格功能模型,基于OGSA(open grid service architecture)框架提出了基于Web服务的网格层次体系结构,并将Web服务工作流引入到网格任务描述中,给出一种Web服务与网格技术相融合的机制,介绍了基于Web服务的网格支撑环境WebSASE4G的总体结构和设计原理,为基于Web     

Collaboration through computation: incorporating trust model into service-based software systems

The open and dynamic nature of service-based software systems necessitates spontaneous and trustworthy interactions between collaborating entities. Service providers are exposed to users spanned across multiple organizational domains, so can be exploited by potentially untrustworthy service requestors. Given that, service providers need to trust requestors before granting them with services. Trust encompasses a number of quality attributes (e.g., security, competence, honesty) and helps in dynamic decision making. In this paper, we present a trust-based service collaboration approach, facilitated by the analysis of service-based interactions between service providers and requestors, and recommendations between service providers. Service providers exchange recommendations to convey their trust on requestors. This collaboration is quantified using our proposed trust model, called CAT, a Context-Aware Trust model based on service-based interactions by considering services as contexts. We identify a number of collaboration-based trust properties including risk and context-awareness and incorporate them in CAT. A context-similarity parameter is introduced to decide on similar services. A time-based ageing parameter is proposed to decrease trust values over time without any further interactions. Direct and indirect recommendations from other service providers are included in total trust calculation, with a path-based ageing parameter applying over indirect recommendations. A mechanism to calculate the accuracy of recommendations is proposed to differentiate between reliable and unreliable recommendations. These calculation schemes are employed in a trust-based service collaboration algorithm to automatically decide on granting services to requestors. The approach is elaborated using examples from file sharing applications, and successfully evaluated by implementing a prototype service-based file sharing grid. This research is partially funded by the Natural Sciences and Engineering Research Council of Canada (NSERC).     

Web服务聚类方法的研究和改进

Web服务的聚类能够改善基于服务的应用如服务发现、组合和QoS预测等.然而目前的聚类方法在相似度度量和信息预处理方面存在一些不足.提出Web服务的QoS和功能两种相似度模型,从不同角度度量服务间的相似度.在此基础上,提出一种特殊的考虑到编程风格和命名规则的预处理方法.最后结合SCAN算法实现了本方法并设计了对比实验对提出的方法进行验证.实验结果表明提出的模型和方法能够有效地提高Web服务的聚类效果.     

基于服务交互行为的复杂服务协同网络建模

随着分布式计算技术的发展,以自治的服务协同与互操作为主要构造手段、结构与行为随需而变的面向服务的软件系统已成为当前主流的软件架构,分析并理解服务交互行为对于这类复杂软件系统的开发、维护和运营具有重要意义.针对面向服务的软件系统中基本构成元素Web服务的复杂交互执行行为,考虑到服务自治性及系统规模化所带来的复杂性,借鉴复杂网络建模分析方法,提出了一种考虑服务行为特征的服务动态行为生长演化模型.模型首先以真实服务的服务结构数据为基础,以服务间参数关联关系为核心,通过参数匹配建立服务结构网络作为基本连通性约束,代表可能发生交互关系的服务.然后,基于服务间的择优选择、组合交互及动态重组等特性,对面向服务的软件系统生长演化及动态执行行为进行了仿真建模.在Seekda及QWS数据集上进行了仿真实验,结果表明:与传统的软件系统的层次性结构有所不同,由自治的Web服务所构成的软件系统具有更强的模块性;与系统中个体服务演化规则,如择优连接及动态重组相比,服务结构网络的性质对系统最终形态有更重要的影响,相关结果对大规模服务软件的构建及分析具有重要的指导意义.     

QoS aggregation for service orchestrations based on workflow pattern rules and MCDM method: evaluation at design time and runtime

Service consumers satisfaction is considered today as one of the main concern to be ensured by service providers, especially with the spread of concurrency and the increase of functionally equivalent services. This satisfaction is closely related to quality of service (QoS) perceived by service consumers. In this context, we propose an approach to determine the satisfaction degree corresponding to the QoS of service-based applications, with regard to service consumers’ QoS expectations. Our approach is based on a preference model, which is built only on the basis of service consumer’s provided information. This preference model is also based on the 2-additive Choquet operator that takes into account preferential dependencies. In this paper, we target both design time and runtime aggregation of QoS of service-based applications.     

面向业务应用的服务发现研究

现有的服务发现研究大多基于功能,以服务为粒度考察服务.而服务是以操作为粒度与用户进行交互的.服务发现与使用粒度上的差异,使服务不能发挥最大效能.为此提出了一种从业务层面,以操作为粒度,考察服务对用户需求业务适用程度的服务发现方法.通过定义面向业务应用的服务与用户需求描述模型,建立领域业务应用本体为服务提供者和使用者的业务级交互奠定基础.通过服务与用户业务需求的深层匹配,在发现可用服务及其操作的同时,对服务的业务规范性和业务完备性进行评估.最终给出了一种面向业务应用的服务发现方法.     

基于语义规则的Web服务发现方法

语义Web服务发现问题研究的核心内容是服务描述与对应的服务发现方法。服务描述分为服务请求描述与服务发布描述,但目前的服务发现方法,并未将请求描述与发布描述分开,以比对服务请求描述与服务发布描述中对应部分作为匹配依据,导致服务请求描述构建困难以及发现结果不够理想。提出以语义规则刻画服务请求描述,以本体构建服务发布描述,进行有效的以语义规则驱动的Web服务发现。对语义规则添加影响因子使得服务匹配精度可以通过匹配度来度量,并按照给定的调节系数来决定最终匹配是否成功。最后以OWL-S TC V2测试服务集合进行了对比实验,证实该方法有效地提高了查全率与查准率高,特别是Top-k查准率。     

利用聚类优化语义Web服务发现

针对传统Web服务缺乏语义造成注册中心返回结果不精确的问题,提出了一种用OWL-S提供语义支持,并据语义相似度将Web服务聚类的解决方法。该方法应用OWL-S实现Web服务的语义描述,采用凝聚的层次聚类的Single-Link算法将相似Web服务聚类,快速定位并返回最合适的服务,提高了服务发现的精确性。     

Service Discovery and Negotiation With COWS

To provide formal foundations to current (web) services technologies, we put forward using COWS, a process calculus for specifying, combining and analysing services, as a uniform formalism for modelling all the relevant phases of the life cycle of service-oriented applications, such as publication, discovery, negotiation, deployment and execution. In this paper, we show that constraints and operations on them can be smoothly incorporated in COWS, and propose a disciplined way to model multisets of constraints and to manipulate them through appropriate interaction protocols. Therefore, we demonstrate that also QoS requirement specifications and SLA achievements, and the phases of dynamic service discovery and negotiation can be comfortably modelled in COWS. We illustrate our approach through a scenario for a service-based web hosting provider.