Research On Key Techniques Of Web Services Composition

With the ability to realize the interoperation of applications on the internet, web service has been a kind of promising integrating technology. A basic requirement of web services is the composition of web services, that is, to compose the existed web services to propose a new value-added function, which has become one of the most important features of web services. At present, the composition of web services has been a hot topic in research field; some standard web service choreography proposals, such as BPEL4WS or WSCI, have also been proposed. However, for these specifications there doesn't exist a unified standard; and even for themselves, these specifications still have a lot to develop and improve.The composition of web services involves the selection, composition, verification and optimization of web services. In this paper, beginning from the basics of composition, we develop the method to select the optimum web services based on the normal of application; then, propose the automatic technology for web services composition to meet the customized requirements of the users; furthermore, we put forward a verification algorithm to analyze the correctness of the composite flow of web services. The main contents include:1. A method to select the optimum web service. First, this method defines and collects the subjective reputation values, then calculates the objective quality values based on the QoS model of web services, and at last, educes the optimum application-oriented web service candidates. And also the evaluating system based on the feedback is established.2. A flexible workflow model. This model formally describes the actions of each web service, develops the automatic composition method for web services based on the task dependencies to meet the customized requirements of the users. And the proposed verification algorithms and the dynamic compensating mechanism make the model more practical.3. The bottom-up and top-down analysis methods for web services composition. Based on the FSA model of web services, put forward two kinds of verification methods. In the bottom-up method, we define the compatibility conception of web services in composition by introducingthe client/server relationship. Then, based on the conceptions, we design the analysis algorithm to verify the correctness of a composite flow. In the top-down method, we first propose a framework to describe the relationship between the atomic services and the composite service, then specify the generated global conversations in composition, and design the algorithms to verify the correctness of global conversations and the projection methods of the global conversations. For the correct global conversations, design the behaviors of each atomic web service based on the results of projection. 4. Implement the prototype system based on the composition model andthe analysis methods. The above results expatiate the key technologies of web services composition,which can be not only applied to the B2B business applications, but also have thepromising the application future in scientific research fields, such as bioinformatics,weather forecasting, distributed computing and the grid service.This work is partially supported by the National Basic Research Program (973)under grant No. 2005CB321905, the Chinese Hi-tech (863) Projects under the grantNo. 2002AA4Z3430, and No. 2002AA231041.