| 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... |
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