Research On QoS Prediction Of Web Composite Services

Web Service Composition (WSC) takes Web services as basic elements and aggregates them to Web Composite Services (WCS) with more complex functions according to the application requirements. Although WSC is driven by function, QoS is equally important to function, as neither WCS with unsatisfying function nor with unsatisfying QoS can meet the users' requirements. So it is very necessary to judge whether WCS designed according to function requirements meet the QoS requirements, and to choose WCS with better QoS from those with familiar functions. And this is based on the QoS prediction of WCS before the WCS execution, and the prediction will be taken as the standard of judgment and selection. Now the research on QoS prediction of WCS is in its infant, and the research result is limited. The paper concentrates on the improvement of feasibility and accuracy of the approach on QoS prediction of WCS, and the main innovations are as follows:(1) An architecture for QoS definition is proposed, and the architecture can meet the requirements of QoS prediction of WCS on QoS definition and suitable for the prediction research. The architecture is based on the QoS Dimension Class, and provides general and multi aspects and multi perspective QoS definition structure for QoS prediction, and support the expansibility of QoS attributes of Web Services.(2) A workflow model for WCS process is proposed, and a novel QoS prediction algorithm is proposed based on the model. The approach is defined with mathematic language, and has higher level of abstraction to the approach in existence. The approach can support more QoS attributes and the prediction result is more comprehensive. (3) A model-driven architecture for QoS prediction of WSC languages is proposed, and the approach for QoS prediction of BPEL processes is proposed based on the architecture. The approach has good feasibility and accuracy.(4) An approach for QoS prediction of WCS with transactions is proposed. We analyze the relationship between Web transactions and WCS execution processes, and provide the method to estimate the execution processes of WCS according to the exception handler policies of the transactions in the WCS. And the QoS prediction algorithm is proposed based on the execution processes estimation. And the approach has good feasibility and accuracy.