Study On Methods Of Web Services Discovery And Composition Based On QoS Technology

With the advent and popularization of e-commerce, it is requisite that the distributed and heterogeneous business applications can be integrated and intemperate with each other in the environment of Internet. And it is also requisite that the appropriate business applications over the Internet can be rapidly and automatically found according to the demand and that they can be composed to meet the demand if there exist no individual business application to meet the demand. Web services technology is quite promising for the integration of business applications and service composition. Web services are more coarse-grained and operate at a higher level of abstraction.In the new service-oriented application environment, under the boost of requirements-driven, web Services discovery and composition with QoS-assured has turned into a primary research field in web services. In the past few years, many issues have been addressed. Recently web services discovery algorithm is lack of flexibility. In each node of function processes, there exist lots of web services with the same function and different QoS. To select a right one exactly with the global QoS-guaranteed, related research had some disadvantages. There have not some works on automatically constructing web services function flow. Weaknesses in the aspects hamper the wide deployment of web services. How to resolve these issues ideally is an open problem.This dissertation does a research on the discovery and automatic composition based on QoS by using of knowledge and methods of ontology, graph theory, genetic algorithm etc. The main points of our work are described as follows:1. A discovery and composition framework based on QoS is presented.In the framework discovery and composition based QoS is divided into six phases of receive of use requirement, services discovery, design of function flow, selection of aware-QoS services, executing of composition, evaluation of result. The framework can support automatically construction of the function flow and global optimal selection of the web services based on QoS.2. A QoS-aware method called WSSM-Q is present for web service discovery.To resolve the problem that web services discovery algorithm is lack of flexibility a QoS-aware method called WSSM-Q is present. A set of QoS categorization tModels is defined in the method to describe the QoS attributes of a web service. QoS advertisements of service providers are represented by QoS quantification values. QoS requirements of service consumers are represented by constraint and preference values. The matching rules classified three levels are defined and match functions is introduced to compute service similarity. Web services to meet the requirements of consumers are discovered by four phase algorithm. Because of no need for changes in the inner structure of WSDL and UDDI, it is easy to implement the method through the direct extension to existing protocols. The WSSM-Q is proved to be feasible and effective by high precision and efficiency of the prototype.3. A new method of automatically constructing web services composition flow based on PDG was presented.Based on the fact that current web services composition flow was designed by human, a new method of automatically constructing web services composition flow based on PDG (parameter deduce graph) was presented. Firstly the predicate form of web services was represented. Establishment of four relations in the PDG and the constructing algorithm was conduced so as to form the graphic models of web services composition. Then by definition of complete relevance matrix in the PDG and operation of combination of rows in relevance matrix, the PDG was converted automatically into SCFG (web services composition flow graph) that contains service-vertex and edges which indicate dependence relations among web services. Theoretical analysis and experimental results demonstrates the feasibility and efficiency of this method.4. A GODRP algorithm is presented for QoS-aware web services selection.In order to select a global optimal plan in a lot of execution plans with the different QoS, a GODRP (global optimal and dynamic replanning) algorithm is presented. A position matrix coding scheme was used to express simultaneously all of composite paths and replanning information in the algorithm. The quality of the services composition was improved by means of calculating Hamming Distance of QoS among individuals. It was solved that the algorithm's executive time impairs the QoS of the services composition by prescribing a total time limit and implementing a fine solutions reservation strategy. Experimental results indicate the feasibility and efficiency of this algorithm. Comparison with similar studies, the algorithm provides a more integrated and effective QoS scheme of services composition in dynamic environment.