Research On Dynamic Web Service Composition And Performance Analysis With QoS Assurences

Web Service extracts the advantage of distributed computation, Grid computation and XML, and solves the problems of heterogeneous distributed computation and data reuse. Web Service has the characters of inter-operation, multi-platform and loose coupling, so it becomes the leading development trend of WWW. But single Web Service has limited function, service increment and service reuse can be obtained only through combining multiple Web Services. Thus, the potential of Web Service can be brought into play.The environment of distributed, heterogeneous and multi-autonomous-fields WAN (wide area network), which is represented by Internet, requires Web Service Composition to satisfy higher demands. The dynamic change of the runtime environment and user requirements desire that Dynamic Web Service Composition can break away from the static composition mode, rectify itself so that satisfy the dynamic characters of WAN and provide efficient, cheap service composition.Under satisfying the precondition of functional demands, the performance of compositive service is the key to capture users, represented by the quality of service provided by it. As the development of Web Service, service functionality continually subdivides and deepens, and users have higher and various demands of QoS (Quality of Service). The capability of providing compositive services with QoS assurance is the necessary condition that Dynamic Web Service Composition can has practicability.In the context of WAN, this dissertation employs both simulation method and mathematic method to study the methods of framework, architecture, building conceptual model, building performance model, performance simulation, performance analysis and performance optimization of dynamic web service composition from the aspects of building model, performance analysis, performance optimization and so on. A trans-whole-length example: Products Order Web Service Composition contrastively validates these models and methods presented in this dissertation. The main points of the dissertation are described as follows:(1) It presents a dynamic web service composition application framework based on Service integratorAiming at the characteristic of dynamic web service composition under the wide area network environment, this dissertation presents a kind of application framework based on Web Service Integrator, introduces the architecture and mechanism of the Web Service Integrator.(2) It presents the conceptual model and meta-model of the Dynamic Web Service Composition and modeling method supporting iterative designFor the shortcoming of Web Service Composition modeling method directly based on Petri Net, This dissertation presents a conceptual model: DWSCHM, which comprises three-tier views. DWSCHM model supports iterative design method from top to bottom and form abstract to concreteness through user view, design view and instance view. DWSCHM model has the advantage of comprehension and description of operation logic. And DWSCHM model can describe composite service from various abstract levels, which improves the reusability of the model. Aiming at the dynamic changes of the runtime environment and user's demands, this dissertation presents a dynamic modeling method based on DWSCHM model. Through adjusting model at runtime, Composite service is able to fit the change of environment and user demands, avoid to be cancelled.(3) Aiming at the performance analysis and performance optimization on the design stage of dynamic web service composition, it presents a simulation-based performance model, performance analysis and optimization method of composite service.The performance indexes can be divided to two classes: time-interrelated and time-irrelated. This dissertation presents a composite service performance simulation model supporting stochastic time—STPM and corresponding simulation method. By extending STPM model, this dissertation presents a performance simulation model supporting time-irrelated characters—STPM+. This dissertation designs and implements a Visual performance simulation tools—VisualWSCPE supporting STPM+ model, introduces performance simulation and analysis methods of composite service based on VisualWSCPE tools.(4) Aiming at the performance analysis and performance optimization on the running stage of dynamic web service composition, it presents a performance model, performance analysis and optimization method based on mathematic analysis.This dissertation discusses two kinds of performance analysis methods respectively based on Markov Process and performance equivalent facilitation, introduces the basic principle of the Dynamic Web Service Composition performance optimization, presents a Web Service selection optimization method based on GA, and describes work mechanism and main algorithms of the key part—genetic selector. By comparing to random selection method, experiment results show the advantages of the Web Service selection optimization method.