Research On The Approaches For Web Services Composition

Web service composition plays an important role in improving the reusability and interoperability of software systems especially under the Internet environment.With the development of B2B business,the composition of the web service will be the main form of inter-enterprise collaboration.Because web services in heterogeneous environment may run on different platforms, be created by different ways,implemented by using a different programming language, provided by different service providers,how to implement the web service composition will be the the focus of research in web service domain.Current web service technologies such as WSDL,UDDI and BPEL4WS can only provide the description on syntactic level but can't express semantic information which makes that requesters and providers can not understand the message conveyed between them and the automation of web service can't be implemented. With the rapid development and gradual improvement of the semantic web technologies especially semantic markup language OWL web ontology,to engage semantic web technology to intelligently integrate various web service resources attracted a growing academic interest in the study and semantic web services was then proposed. And the automatic composition of semantic web services received extensive concern from the beginning.With the improvement of SOA architecture, the larger amount of web services immerged on Internet, the efficiency of the web service composition will put an important role on the development of the dynamic composition.This thesis analyzed web service composition related methods and the current research status,studied many kinds of semantic description of web service,and on the basis of OWL-S, studied web service composition methods,especially studied how to compose web services dynamically and do our best to ensure the efficiency of composition methods in the presence of massive web services.The major content and the achievements of this thesis are as following:(1) First,we analyzed the character and demand of the service oriented architecture and web service composition,then analyzed the research basis of automatic web service and its research area,importantly introduced the semantic web service description language called OWL-S,which settled the theoretical basis of our dynamic composition methods and its efficiency improvement.(2) Proposed a Web service dynamic composition algorithm based on description logic. Description logic is a formal representation of knowledge.One of the most significant feature is a formal, logic-based semantics, the other is its ability to see reason as a kernel service. We formally describe the web service by using description logic. Each of the inputs and outputs of web service requests is understood as concept in description logic.The semantic similarity between concepts was given according to the five match degree in description logic.The algorithm considered the semantics of Web service,implemented dynamic composition of web service according to user's request,increase the quality and efficiency of web service composition.With the use of DL's ability to express the semantics, composition of Web services can be judged according to the semantic relation between concepts which increase the success probability of composition.(3) Proposed a Web service composition algorithm based on annotated ontology, which can improve the dynamic Web service composition's efficiency.With the number of Web services available on the Internet becoming larger and larger, How to quickly retrieve the web service semantically annotated with the domain ontology during composition process will be the key role of the development of Web service composition. We started from annotating the domain ontology with web services and used OWL-S to formally describe the web service,applyed the interface match algorithm,classified the Web services according to the concepts of the service's input and output parameters, then the search space used by semantic matching was decreased and thus the efficiency of the web service composition was enhanced.A concurrent algorithm also was proposed.The imitation experiment result showed the algorithms could improve the web service composition efficiency.(4) Proposed a hybrid web service composition methods based on caching pool. Static composition takes place during design-time when the architecture and design of the software system are planned. This may work fine as long as the web service environment-business partners,and service components does not, or only rarely changed.The service environment is a highly flexible and dynamic environment.Ideally,service processes should be able to transparently adapt to environment changes.We analyzed the advantage and disadvantage of static composition and dynamic compostion,proposed a hybrid web service composition method based on caching pool.The descriptions of the composed web service were stored in the caching pool,and the caching space was managed by using appropriate replacement algorithm.The common composition service can be composed once and used many times to save the composition time and in the meantime it maintaines the flexibility of the dynamic web service composition according to user's request.We proposed the priority of composite web service and replacement degree which can be used to ensure the storing of the composed web service which was the most common and was the most difficult to compose.These measures ensure to improve efficiency of composition.(5)Defined a web service registry architecture and proposed a semantic web service discovery algorithm oriented for composite web service.The main areas of research on Semantic Web services include discovery, selection, composition and execution of web service. An infrastructure----the semantic web service registry architecture is needed to ensure these tasks to work well. This thesis proposed architecture for web service registration. In which, a service registry structure was defined, the registration algorithm of atomic web services and composite services were implemented, and semantic web services discovery and composition can be done.In it a method to maintain the registration center also proposed. With the web service discovery algorithm, we can both discover atomic services and composite services.The reuse of composition can be obtained and the efficiency can be improved.The work and result in this thesis can be directly used in the web service composition, and has some theoretic and actual value on composition efficiency improvement.