基于SLA的语义Web服务组合
摘要
随着Web服务技术的发展,国内外众多学者围绕Web服务组合问题展开了广泛而深入的研究,并取得了一些有价值的探索性研究成果。利用现有的单个Web服务进行服务组合,不但满足了用户的需求,而且还提高了现有服务的复用率。但作为一项新兴的研究课题,其中还有许多亟待解决的问题。其中,以往的研究大都认为服务的质量越高,用户就越满意。其实不然,由于实际应用中会受具体条件的限制,用户可能会对服务质量提出某些特殊要求。
服务水平等级协议(SLA, Service-Level Agreement)是服务提供者和用户之间协商签订的一个正式合约,合同规定了在服务提供过程中双方所承担的商务条款,是在服务品质、优先权和责任义务等方面达成的协议。SLA的提出既满足用户的需求,又可以实现服务提供者利益的最大化,从而有效保障了交易双方的权益。本文围绕基于SLA的Web服务组合问题展开研究,主要完成了以下工作：
1.结合组合服务的一般流程和SLA协议的特点,提出一种基于SLA的服务组合框架。其中支持组合服务提供商和用户之间通过Agent自动建立SLA协议,在服务组合过程中,由组合服务提供商根据服务质量对服务分级,提供不同的SLA协议,用户进行选择确定后即建立了正式的SLA协议,SLA协议使用WSLA(Web Services Level Agreement)语言描述；并且该框架实现了服务组合的自动化与动态性,自动进行服务组合与服务选择,根据服务运行情况,适时对组合服务进行替换,提高了组合服务的健壮性。
2.提出一种基于语义的Web服务组合方法。将服务的I/O表示成本体概念的集合,利用本体概念间的语义相似度,使用深度优先原则,能自动、高效地生成满足用户需求的组合服务。同时为表示出所请求组合服务中各服务之间的相互依赖关系,定义了用户请求的本体依赖关系,克服了一般自动服务组合方法在这方面的缺陷。仿真实验证明了该方法的可行性。
3.为使组合服务在满足SLA协议规定的基础上达到性能的最优化,提出一种基于多种群混合遗传算法的服务组合方法。通过将SLA协议中的具体的QoS约定转化为影响遗传算法适应度函数的因子,利用多个种群独立的使用不同的进化参数进化,增加了个体的多样性,扩大了搜索的范围,模拟退火操作加速了收敛速度,实验证明该方法有效的解决了服务组合问题。
4.为适应网络环境的不确定性和Web服务的动态性,提出一种基于SLA的动态Web服务组合方法。通过分析动态环境下组合服务出现服务失效或QoS指标偏离的原因,提出若使用单个服务替换方法产生的组合服务性能比原方法性能优越,则在组合中只对QoS异常的服务进行更换；否则在备用的组合服务执行方案中根据实时QoS性能选择其中较优的进行升级或进行服务重组合,保证了组合服务的质量。最后仿真实例证明了本方法的可行性和有效性。
With the development of Web services technology, domestic and foreign scholars around the Web service composition issues carried out extensive and in-depth study and obtained some valuable results of exploration. Use of the existing single Web services to do Web services composition, not only to meet the needs of users, but also improves the reusability of existing services. As a new research topic, there are many problems to be solved. Among them, most of previous studies thought the higher quality of service, the more satisfied users.But in fact, the user may have made some special quality of service requirements, because the practical application would be subject to specific conditions.
SLA (Service-Level Agreement) is a formal contract between users and service providers, agreed upon the actual delivery of services quality, priorities, responsibilities and obligations of both parties.The proposed SLA meet the needs of users, and also fulfill the best interests of service providers to effectively protect the interests of both transactions. The Master thesis mainly focuses on the SLA-based composition of Web service issues and does some researeh, the main research work is as follows:
1. Combining the general flow of composite services and the characteristics of SLA protocol, the paper provides a SLA-based service composition framework, which has the following two characteristics: First, it supports the composite service providers and users through the Agent automatically create SLA agreement. In the service composition process, the composite service providers do service classification according to the quality of service and provide different SLA agreements. After the user selection, a formal SLA agreement has been established, which uses WSLA (Web Services Level Agreement) language to describe. Second, it achieves the automation of service composition to support automatic service composition and service selection. According to the service operation, the composite service will timely replaced to improve the robustness.
2. The paper propose a semantic-based automated Web service composition method.Which expressed the I/O of services as the set of ontology concepts, Using semantic similarity and depth-first principle, can automatically and efficiently generate a composite services to meet user needs. At the same time, as the interdependence between the services, we define the dependence of Ontology in user requests to overcome the general method of automatic service composition in this deficiency.
3. In order to meet the SLA agreement and achieve the maximum the QoS performance, a semantic web service composition method based on Multi-population hybrid genetic algorithm is proposed, which translated the Specific QoS agreement in SLA into Genetic factors of fitness function, increased the diversity of the individuals and expanded the scope of the search Using multiple independent populations with different evolutionary parameters of evolution, parallel simulated annealing operation accelerated the convergence speed.So the simulation experimental results show the services composition problem effectively to be addressed.
4. To fit the uncertainty of network environment and dynamics of Web services, a SLA-based Dynamic Semantic Web service composition method is proposed, which analyzed the reason of service failures or QoS indicators deviation, proposed to replace the anomalous service if the performance of composite service using a single service replacement method is superior than the original; Otherwise, to update the composite services using the optimum under Real-time QoS properties in the backup composite plan or recomposition to ensure the quality of service composition. Finally simulation results show the feasibility and effectiveness of this method
服务水平等级协议(SLA, Service-Level Agreement)是服务提供者和用户之间协商签订的一个正式合约,合同规定了在服务提供过程中双方所承担的商务条款,是在服务品质、优先权和责任义务等方面达成的协议。SLA的提出既满足用户的需求,又可以实现服务提供者利益的最大化,从而有效保障了交易双方的权益。本文围绕基于SLA的Web服务组合问题展开研究,主要完成了以下工作：
1.结合组合服务的一般流程和SLA协议的特点,提出一种基于SLA的服务组合框架。其中支持组合服务提供商和用户之间通过Agent自动建立SLA协议,在服务组合过程中,由组合服务提供商根据服务质量对服务分级,提供不同的SLA协议,用户进行选择确定后即建立了正式的SLA协议,SLA协议使用WSLA(Web Services Level Agreement)语言描述；并且该框架实现了服务组合的自动化与动态性,自动进行服务组合与服务选择,根据服务运行情况,适时对组合服务进行替换,提高了组合服务的健壮性。
2.提出一种基于语义的Web服务组合方法。将服务的I/O表示成本体概念的集合,利用本体概念间的语义相似度,使用深度优先原则,能自动、高效地生成满足用户需求的组合服务。同时为表示出所请求组合服务中各服务之间的相互依赖关系,定义了用户请求的本体依赖关系,克服了一般自动服务组合方法在这方面的缺陷。仿真实验证明了该方法的可行性。
3.为使组合服务在满足SLA协议规定的基础上达到性能的最优化,提出一种基于多种群混合遗传算法的服务组合方法。通过将SLA协议中的具体的QoS约定转化为影响遗传算法适应度函数的因子,利用多个种群独立的使用不同的进化参数进化,增加了个体的多样性,扩大了搜索的范围,模拟退火操作加速了收敛速度,实验证明该方法有效的解决了服务组合问题。
4.为适应网络环境的不确定性和Web服务的动态性,提出一种基于SLA的动态Web服务组合方法。通过分析动态环境下组合服务出现服务失效或QoS指标偏离的原因,提出若使用单个服务替换方法产生的组合服务性能比原方法性能优越,则在组合中只对QoS异常的服务进行更换；否则在备用的组合服务执行方案中根据实时QoS性能选择其中较优的进行升级或进行服务重组合,保证了组合服务的质量。最后仿真实例证明了本方法的可行性和有效性。
With the development of Web services technology, domestic and foreign scholars around the Web service composition issues carried out extensive and in-depth study and obtained some valuable results of exploration. Use of the existing single Web services to do Web services composition, not only to meet the needs of users, but also improves the reusability of existing services. As a new research topic, there are many problems to be solved. Among them, most of previous studies thought the higher quality of service, the more satisfied users.But in fact, the user may have made some special quality of service requirements, because the practical application would be subject to specific conditions.
SLA (Service-Level Agreement) is a formal contract between users and service providers, agreed upon the actual delivery of services quality, priorities, responsibilities and obligations of both parties.The proposed SLA meet the needs of users, and also fulfill the best interests of service providers to effectively protect the interests of both transactions. The Master thesis mainly focuses on the SLA-based composition of Web service issues and does some researeh, the main research work is as follows:
1. Combining the general flow of composite services and the characteristics of SLA protocol, the paper provides a SLA-based service composition framework, which has the following two characteristics: First, it supports the composite service providers and users through the Agent automatically create SLA agreement. In the service composition process, the composite service providers do service classification according to the quality of service and provide different SLA agreements. After the user selection, a formal SLA agreement has been established, which uses WSLA (Web Services Level Agreement) language to describe. Second, it achieves the automation of service composition to support automatic service composition and service selection. According to the service operation, the composite service will timely replaced to improve the robustness.
2. The paper propose a semantic-based automated Web service composition method.Which expressed the I/O of services as the set of ontology concepts, Using semantic similarity and depth-first principle, can automatically and efficiently generate a composite services to meet user needs. At the same time, as the interdependence between the services, we define the dependence of Ontology in user requests to overcome the general method of automatic service composition in this deficiency.
3. In order to meet the SLA agreement and achieve the maximum the QoS performance, a semantic web service composition method based on Multi-population hybrid genetic algorithm is proposed, which translated the Specific QoS agreement in SLA into Genetic factors of fitness function, increased the diversity of the individuals and expanded the scope of the search Using multiple independent populations with different evolutionary parameters of evolution, parallel simulated annealing operation accelerated the convergence speed.So the simulation experimental results show the services composition problem effectively to be addressed.
4. To fit the uncertainty of network environment and dynamics of Web services, a SLA-based Dynamic Semantic Web service composition method is proposed, which analyzed the reason of service failures or QoS indicators deviation, proposed to replace the anomalous service if the performance of composite service using a single service replacement method is superior than the original; Otherwise, to update the composite services using the optimum under Real-time QoS properties in the backup composite plan or recomposition to ensure the quality of service composition. Finally simulation results show the feasibility and effectiveness of this method
引文
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[3]岳昆,王晓玲,周傲英.Web服务核心支撑技术：研究综述[J].软件学报,2004,15(3)：428-442.
[4]Keller A, Ludwig H. Defining and monitoring service level agreements for dynamic e-Business[C]. In: Proc. of LISA 2002:The 16th Keller A, Ludwig H. Defining and Systems Administration Conf. Berkeley:USENIX Association,2002.189-204.
[5]Cabrera F, Copeland G, Cox B, Freund T, Klein J, Storey T, Thatte S. Web services transaction. http://www.infosys.tuwien.ac.at/Teaching/Courses/IntAppl/Papers/ ws-transpec.pdf.
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[8]Dan. A, Ludwig. H, Pacifici. G. WS differentiation with SLAs. http://www-128.ibm.com/developerworks/webservices/library/ws-slafram.
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