Research On Web Services Composition And Related Technology

Web Services are considered as self-contained, self-describing, modular applications that can be published, located, and invoked across the web. Nowadays, an increasing amount of companies and organizations implement their core business and outsource other applications as Web Services over Internet. However, single Web Service cannot satisfy all the functionality needed by the user. It is imperative task to study how to compose Web Services into a new service.The Web Services Composition is the natural evolution of software component composition, which aims at software development without reinventing the wheel. However, in the Web Services environment, it poses several additional challenges with respect to component-based software engineering.Firstly, Web Services are distributed naturally. Web Services are deployed in a volatile and dynamic environment - the Internet. Web Services can be deployed or undeployed at any given time. Network break down can also make Web Services unavailable. Distributed nature of Web Services can also bring advantage to system's performance and throughput.Secondly, traditional component-based software engineering assumes that the component is composed by expert, such as professional software developer. This service develop method cann't meet the rapid change requirement of the user. As the dynamic nature of Web Services, providing on demand service composition method is very important.The distributed natures of Web Services and rapid changing user requirement are the key challenges addressed by this dissertation. The main contributions are as follows:1. Driven by the dynamic requirement of the user, we provide a method to compose information gaining Web Services. The proposed method automatically composes Web Services directly according to the customers' requirement, and then executes the composed services to achieve the customers' goals. Based on the historic records of Web Services compositions, this method uses a heuristic approach to adjust the composition scheme. Experiment results show that the method is well fits to the volatile environment and yields better performance over other algorithms.2. For the Web Services Composition of information gaining Web Services and world altering Web Services, the dissertation provides a user preference aware approach to Web Services compostion. The key of this approach is to support the users' preferences and ensure their satisfaction. In the dissertation, the users' preferences and satisfaction are modeled as Fuzzy Constraint Satisfaction Problem. Based on this modeling, the dissertation introduces how to use Hierarchical Task Network with Branch and Bound Method to compose Web Services. The experiment results show that this approach improves the users' satisfaction with trivial performance loss. 3. To cope with the dynamic nature of Internet, This dissertation uses policies to capture the common part of Web Services exception handling and presents a Multi-Policy Exception Handling System (MPEHS) to provide system level solution. In current Web Services Compositon method such as Business Process Execution Language for Web Services (BPEL4WS), exception handling is often in ad hoc way, it is up to the service developers to define how to deal with these exceptions. MPEHS add functionality to handle exception underlying the BPEL Engine. The MPEHS's policies can be reused in different BPEL processes and simplify the work of BPEL process developer.4. There are two models for the execution of Web Services Composition. They are centralized model and distributed model. Contrast to centralized model, Distributed Web Services Composition model can improve system's performance. However, different partitions of same service flow also get different throughput of system. This paper studies the distributed partition problem of Web Services composition and proves that it is NP-Hard. The research solves this problem use genetic algorithm. Experiments showed satisfying result of the algorithm.