Research On Key Technologies Of Automatic Web Services Composition

Enterprise applications integration is one of core problems in information field, and Web services are currently the standard frameworks for constructing cross-enterprise distributed applications. Web services composition is to integrate service modules and has become the bridge between information infrastructures based on Web services and enterprise applications integration. Only when application programs and business processes can together implement complex business applications through Web services composition, could Web services technique be brought into play. Therefore, the problem how to compose distributed and autonomous Web services available into new enterprise business applications has become a hotspot problem of software engineering.With the requirements of inter-enterprise application integration in open computing environment being the research background, we have investigated some important issues of automatic service composition. The contributions of this dissertation are as follows:(1) Summarizations and analyses. First of all, we have summarized the research progress on services composition home and abroad, which can be classified into three main categories, namely workflow based, artificial intelligence planning based and program synthesis based ones. For each of the three categories, representative methods have been described as examples and their advantages and disadvantages been analyzed.(2) Automatic semantic annotation method for Web services. Service description is the base of services composition. Semantic annotation for services has become an effective approach to get the semantic descriptions for Web services. In this dissertation, we divide semantic annotation process into two sub-processes: domain location and concept mapping. Existing automatic service annotation approaches mainly concentrates on the solution of concept mapping. Aimed at the solution to domain location problem, we present an algorithm called MD-kNN40D (Multiple Domains ANN for Ontology Discovery) based on the idea of machine learning. Experiment results show that MD-kNN40D is an effective supplement to existing services semantic annotation approaches.(3) Efficient semantic based services matching method. Service discovery plays an important role in services composition. In this dissertation, we have presented an approach to services matching called SMOSH (Services Matching On Services Hierarchy), which hierarchizes services by exploiting the automatic reasoning mechanism of OWL ontologies. We have formally proved that the constructed hierarchy can help much to increase the matching efficiency. The results of simulation experiments show that, compared with representative approaches available, SMOSH keeps relatively good performance and can respond to services request in much shorter time.(4) Similarity measure mechanisms for semantic Web services. Service similarity measure is useful to quantify the matching extent of candidate services with requests, to make a ranking of the candidate services, and to enrich the flexibility of service matching. Semantic similarity measure of OWL concepts is the base of similarity measure of services that are annotated using OWL concepts. We have presented a structural similarity measure mechanism of concept descriptions, which elicits the underlying semantics by querying the knowledge base and assesses the information content of concept expresssions.(5) Efficient algorithms for automatic services composition. Services composition problem is NP complete. We have proposed a novel automatic services composition method based on graph called ASC-Graph (Automatic Services Composition Based on Graph) in this dissertation. ASC-Graph consists two phases. The first one is to construct the composition planning graph, by which we can justify the satisfiability of composition problem in polynomial time. The second one is to search the composition solution, namely to find the optimal solution for specific composition problems. Aimed at the problem of composition solution search, a search algorithm has been presented. The results of simulation experiments show that ASC-Graph can solve the composition problem of large-scale services effectively.(6) Formal modeling theory for Web services behavior. Service systems include stateful ones and stateless ones. Among the interface operations of stateful services, there exist strict logical and temporal constraints. In this dissertation, we have presented a formal behavior model Service-Net which is based on Colored Petri Net (CP-Net). Service-Net can be used to describe not only the control dependency and data dependency among inner operations, but also the message interactions of services with outer environments as an independent communication system. We comprehensively put into considerations the effects of control flow and data (message) flow on service's inner and interaction behavior, so Service-Net can support comprehensive and precise description and analysis of services behavior.(7) Verification theory and methods for services interaction. Composition of stateful services is interactive, that is, once all component services finish their private sessions, global interaction protocol will be generated. The correctness of interaction protocol is the key to assuring the success of services interactions. Based on the behavior model Service-Net, we have further defined the formal model of services interaction. In addition, the correctness justification criteria of interaction protocol as well as the corresponding verification methods based on CP-Net theory are presented.(8) To apply the behavior modeling theory and the interaction correctness verification methods into real-world Web service execution platforms, we have presented the model transformation rules from the metamodels of the standard Web services flow modeling language BPEL (Business Process Execution Language) to Service-Net construct elements, and thus defined the CP-Net formal semantic for BPEL.To sum up, we present well-evaluated solutions in this dissertation for some key issues of automatic service composition. Our contributions make a nice groundwork for future research and engineering on automatic service composition both in theory and in practice.