Research On Modeling And Mapping Of Web Service Composition

Recently,the development of Web service and service composition is in the ascendant.With the difficulty of a single Web service to meet the increasingly complex business needs,Web service composition has become a hot spot in industry and academia.It can not only improve the reuse rate of Web services,reduce the development cycle and development cost,but also can compose flexibly according to users' changing demand.A number of existing Web services is combined to form a new Web service.The new Web services,as a special kind of system,can provide users with more powerful functions.The modeling,analysis and verification,implementation of the Web service composition are the three most important phases of the Web service composition lifecycle.Many researchers have studied the Web service composition with graphical methods,formal methods,and business process execution languages.But most of the researchers often use a single modeling approach to model and describe all phases,without fully considering the characteristics of each stage.The graphical method is simple,intuitive and easy to understand.It is suitable for modeling stage of Web service composition.But its semantics is described by natural language.It has two senses and inconsistencies,so it is not suitable for Web service composition analysis and verification,implementation stage.The formal method based on the mathematics has a formal analysis and verification methods.It is suitable for analysis and verification stage of Web service composition.But the formal method is highly abstract and difficult to understand,so it is not suitable for the modeling and implementation phase of Web service composition.Business process execution language can able to perform directly in the workflow engine.It is suitable for implementation stage of Web service composition.But the business process execution language is non formal,it involves too many implementation details,the abstract level is not high.So it is not suitable for the modeling,analysis,and validation phases of the Web service composition.At present,there is no organic combination of modeling features and modeling language at various stages in the existing literature,there is a gap between the modeling,analysis,verification and implementation of the Web service composition.This thesis proposes an organic combination method of non formal modeling languages(BPMN and BPEL)and formal modeling language(workflow nets),which fit for different stages with different characteristics.Three stages of Web service composition of modeling,analysis and verification,implementation are covered.It implements the mapping of business process modeling notation to workflow nets and the workflow nets to business process execution language.The goal of seamless connection from modeling to implementation is reached.The main research results are as follows:(1)The problem of the non-standard,different structure but the same semantics exists in the Web service composition.This thesis puts forward seven characteristics of good structure Web service composition,and gives the definition of Web service composition process,Web service composition,good structure Web service composition process,and the definition of good structure Web service composition.The transformation rules from the common Web service composition to the good structure of the Web service composition are given,and the common Web service composition is converted to a good structure Web service composition according to the transformation rules.The problem of the nonstandard and structural diversity in the Web service composition is solved.(2)The BPMN standard specification uses the natural language to define the execution semantics of Web service composition,so it is impossible to analyze the semantic of the Web service composition.The mapping rules between Web service composition and workflow nets are proposed.Petri net defines the semantic of Web service composition and conversion tool named Orch2 PetriNet is implemented between Web service composition and workflow nets.Web service composition and the corresponding workflow is proofed equivalent in behavior using the weak bisimulation.At the same time,correctness of the mapping rules is verified.(3)In view of the commonness of Web service composition,there are three kinds of problems: lack of start events,end events or lack of start events and ending events,the combination of parallel gateways and exclusive gateways,the combination of exclusive gateways and parallel gateways,the unreasonable combination of Web services and so on.With the help of Petri net analysis technology,the semantic errors of Web service composition attribute to a structural problem or a problem of nature in workflow nets.Specifically,for the problem of lacking starting events,ending events or lacking starting events and ending events and mixing gateways in Web service composition,the structure analysis is carried out by corresponding algorithm and existing Petri net verification tools.For the unreasonable problem of Web service composition,the nature analysis is carried out by the Petri network verification tool.For the problem discovered,Web service composition model in the modeling stage is modified and mapped it to workflow nets,detecting whether there are problems of structure and nature of the problem using corresponding tools and algorithm until there's no problem.(4)For the transformation problem of workflow nets to executable business process execution language,the mapping algorithm from workflow nets to business process execution language is proposed.At the same time,the corresponding BPEL code of sequence component,selection component,pick component,loop component and flow components is given.The algorithm uses iterative method repeatedly selecting different types of components,BPEL conversion,simplification of workflow nets,to realize the mapping and transformation of the whole workflow to the BPEL code.In a word,aiming at the three stages of modeling,analysis and verification,and implementation of Web service composition lifecycle,this thesis puts forward relevant theories,methods and technologies at different stages to support the smooth transition from modeling to implementation.Finally,a complete case is used to verify the correctness of the proposed theory and method.