摘要
随着计算技术和网络技术的发展,普适计算成为新一代的计算模式,普适应用系统也随之得到长足的发展。普适计算的理念是“以人为本”,即随时随地为用户提供其所需的服务,而面向服务的架构(SOA)以其灵活的软件构筑方式,被认为是实现动态普适应用的理想软件架构模式,传统的Web服务已经发展为普适服务,服务组合技术也被广泛的运用于动态构建普适应用。然而,由于普适环境中设备计算和存储能力的差异性,以及网络等基础配置的动态性,传统的服务组合技术无法直接应用于普适环境。普适应用需要紧密结合用户和服务的上下文,才能实现按用户需求提供服务。为此,学术界和工业界都开展了广泛的研究,并取得了不少研究成果,但是尚未从真正意义上实现动态的普适服务组合,为用户提供最适当的服务。
为此,我们从如下几个方面展开了研究工作:
(1)基于本体的上下文描述和管理系统
根据上下文的特征,利用语义网技术,建立了多个本体用于描述上下文信息。基于本体的上下文模型既能描述实体的一般特征,适用于大部分领域实体,又能够通过拓展本体属性描述特定个体,具有良好的可扩展性。此外,针对普适环境中语义异构的上下文信息源,提出了上下文预处理机制用于处理原始信息,并将其转化为上下文本体中的标准信息供其他应用使用。
(2)基于Petri网的普适服务过程模型和自动合成技术
采用Petri网作为形式化模型,建立了普适服务过程模型,用于描述普适服务的功能,该模型能有效描述普适服务这样的自治实体以及基于服务组合的松耦合普适应用。在此模型基础上提出了组合服务自动化合成机制。根据用户的输入、期望的输出和期望的动作,自动化生成组合服务规范。
(3)基于上下文的组合服务路径构建
普适服务的异构性导致相同功能的服务性能具有较大的差异,对于已生成的组合服务,系统根据普适环境和用户的上下文选择合适的服务调度策略,并根据该策略选择服务副本,构成组合服务路径,使得由这些服务副本构成的组合服务能够为用户提供最佳质量的服务。
(4)基于移动Agent的组合服务执行
提出了基于移动Agent的组合服务执行机制,采用分布式运行模式,能有效降低数据传输量,克服集中式服务执行带来的单点失效等弊端。此外,进一步讨论了Agent驻留策略和Agent之间的数据传输机制,该技术能进一步降低服务之间的数据传输,并有效防止Agent的重复迁移,从而显著提高系统性能。
本文以普适空间上下文的描述和管理为基础,深入研究了普适服务合成及其相关技术,提出了上下文感知的普适服务自适应合成机制,动态为用户提供所需的服务。该服务合成机制能够根据用户的需求和可用服务动态合成组合服务,并且根据当前上下文生成组合服务路径,为用户提供具有最佳服务质量的组合服务。此外,针对传统集中式的组合服务执行引擎在效率和鲁棒性等方面的问题,提出了基于移动Agent的组合服务执行机制,用于实现组合服务。
With the development of computing technology and network technology, pervasive computing is becoming a novel computing paradigm and pervasive application systems have been developed rapidly. The idea of pervasive computing is human centric, i.e. user can acquire service at any time any place. At the mean time, service oriented architecture (SOA) is considered as the ideal software architecture for pervasive applications. Traditional Web services have been developed as pervasive services and service composition techonology also has been widely used in dynamic constructing pervasive applications. In pervasive space, however, the devices have different computing and storage ability and the network is in dynamic. Thus, traditional service composition technology cannot be applicated directly. In both acadimica and industry, researchers have widely investigated this problem, and gotten several good results. But none of them really achieved dynamic pervasive service composition which provids suitable service for user.
For this,we did research on following subjects.
(i) Ontology based context modeling and management system
According to the characteristic of context, several ontologies are builded to represent context. Ontology based context model is able denote the general characteristics of entities which is suitable to most of domain entities. It also can describe the personal characteristic through extending ontology. Furthermore, for the heterogeneous context source, pre-process mechanism to handle source information and converts the source information into the standard attributes in context ontology are proposed.
(ii) Petri net based pervasive service process model and automatic service composition
Base on Petri net, pervasive process model is builded to describe the function of pervasive services. This model is able to describe pervasive service and such loosely coupled pervasive applications. This paper proposes automatic service composition mechanism based on this model, which can automatically generate service specification according to user's input, expected output and actions.
(iii) Context based composite service path construction
The heregeneous of pervasive service leads to the different performance of service with same function. For the composite service, system gets the best service policy in accordance with the context of both pervasive space and user, based on which the service instances are selected to construct composite service path. This service path can offer best performance for user.
(iv) Mobile agent based composite service execution
Mobile agent based composite service execution mechanism which is a distributed service execution mechanism is presented. It can greatly reduce the data transformation and overcome the centrilized disadvantages. This paper further discusses the agent residing policy and the data transformation mechanism between agents, which can reduce the data transformation and prevent the multi-migration of agent, so that improve the system performance.
Based on the study of context modeling and magament, this paper investigates the pervasive service composition and related technology and proposes context aware pervasive service composition mechanism which can dynamically provide services. This service composition mechanism provides composite services based on users' requirement and available services, and then it generates composite service path based on context, so that offers best composite service. Furthermore, traditional centrilized composite service execution engines are not effective and robost, this paper proposes mobile agent based composite service execution machenism to achieve composite services.
引文
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