On The Approaches For Web Services Composition

How to reuse the existing services, and compose them in an automatic and manageable way to generate a new application system for meeting the dynamic demands of enterprises has become a concern and a hot issue of the industries and academic community. This has also become a technical driving force which pushes Web services to develop forward continuously.The technologies for Web services solve heterogeneous distribution computing and the reuse of code and data by utilizing XML-based standard or proposal such as WSDL, UDDI, SOAP et al and has a high degree of interoperability across platforms as well as a feature of relaxing coupling. Though the Web services promise to integrate business operations, reduce the time and cost of Web application development and maintenance as well as promote reuse of code over the World Wide Web, the existing Web services standards only provide syntactic-level descriptions, so they cannot express semantic for Web services. The lack of machine-processable semantics necessitates human intervention for dynamic discovery and composition for web services, so it is very difficult to meet the need for automated services discovery as well as large-scale services reuse and composition. Semantic Web services composition augments services with semantic information and acquires a consistent knowledge of information about services from concept and definition using ontology base and makes the services interrelated so as to increase flexibility, promote quality and improve accuracy for Web services composition.The aim of this thesis is to find out how to compose Web services into a new service dynamically with BPEL4WS. And this thesis deals with service-oriented architecture, the available Web services composition specification, the intergration of semantic Web service technology with work-flow technology, and the goal-based algorithm for Web services composition and so on. At the same time this thesis points out the problems to be solved in the process of dynamic Web service composition as follow:1. The existing SOA provides a generic deployment and discovery mechanism. Nevertheless, it limits the semantically compatible but syntactically identical or syntactically identical, but semantically incompatible match. So it fails to manipulate the semantic match between advertisements and requests effectively. Thus, it fails to meet the requirements for dynamic Web services composition.2. BPEL4WS makes it possible to bind the services to physical ports dynamically via WSDL, but it fails to provide a concrete method to discover the required service and adjust business processes at runtime in BPEL4WS process.3. With the increasing development and popularity of Web services and semantic Web services, the idea of workflow-driven service composition is becoming a reality. So a method of integrating the semantic Web services with the workflow technology must be found out.4. In the process of the interaction between Web services, the user often hopes to receive the expected results with just one request, but the dynamic and constantly changing Web service environment cannot always provide the relevant Web service that the user requires.First of all, by comparing the business processe implemented by a Business Process Definition Languages (BPDL) with the one by traditional programming languages, this thesis deals with how to compose Web services into a new service statically with BPEL4WS so as to provide solutions for services-based architectures to support business interoperability. Aims at the above-mentioned questions, this thesis deals with how to augment the service-oriented architecture with semantic mechanism and enable the deployment and discovery of Web service be based on semantics in order to support the automatic discovery and binding of Web service. By analyzing the standards and engines of BPEL4WS, the thesis puts forward the methods of Web service composition based on the template of process to overcome the weaknesses of BPEL4WS in dynamically composing the Web services. In order to realize the idea of workflow-driven service composition, this thesis proposes a model for constructing web services workflows by means of integrating research efforts for semantic Web services with workflow technology. According to the formal description of a task, a semantic match-based method is proposed for searching a Web Service chain which solves the problem that the dynamic and constantly changing Web service environment cannot always provide the relevant Web service that the user requires.The contents and the achievements of the thesis are as follow:1. The interaction of distributed, heterogenous and ever changing Web services will inevitably result in semantic differences. The present XML-based SOA fails to support the deployment and discovery of Web services based on semantic description and solve the problem of dismatch caused by semantic differences. In order to enable SOA to adapt to the interaction of Web Services in a more effective way, and aimed at the weak adaptability of available SOA, semantic Web services-based SOA is proposed in this thesis. That is, Web Services are advertised and discovered by augmenting Web Services with rich semantic descriptions. As a result, Web Services will be discovered according to their functional requirements as well as the best quality criteria by this SOA.2. BPEL4WS is the most recently leading player among Web service composition specifications, but it cannot completely meet the demands of dynamic Web service composition. So how to take the characteristics of the existing BPEL4WS specification and its engine into consideration and adapt them for dynamic Web service composition is to be dealt with in the thesis. This paper proposes a Web service composition method based on the template of BPEL process, which can instantiate the abstract process template into a concrete process. Compared with other similar methods, this method has taken the characteristics of existing BPEL4WS specification and its engine into consideration.3. With the growing increase of available web services, there is an ever growing demand to compose web service workflows in order to perform complex business processes. By applying the OWL-S/UDDI Matchmaker to the construction of web service workflows, a model for constructing web services workflows will be presented and a corresponding approach is given in this paper. This model utilizes the semantic descriptions of web services in searching and matching web services automatically, and realizing the automatic construction of web service workflows.4. A approaching goal-based algorithm is proposed for searching web Service chain by adopting the semantic matching algorithm for service profiles, which is based on the web services ontology and the domain-related ontology. With this algorithm, a service chain can be found in accordance with the request for service and can be composed in order to serve needs of requests.The algorithm put forward in the thesis for discovering service chains enriches the previous research achievements. Especially, the "set of concepts" and the "bunch of concepts" introduced and defined formally in the thesis and applying them in the formal definition of service chains are instructive to the discovery of service chains theoretically.