Performance Modeling And Analysis Of Web Services Composition

Web services provide the basis for the development and execution of business processes that are distributed over the network and available via standard interfaces and protocols. Web services have the characters of inter-operation, platform-independent, self-described and loose coupling. Service composition is one of the most promising ideas underlying Web services: new functionalities can be defined and implemented by combing and interacting with pre-existing services. Web services composition refers to the process of composing multiple states-less atomic Web Services into state-full complex applications. Under satisfying the precondition of functional demands, the performance of compositive service is the key to attract users. However, deploying a test-bed system to evaluate Web services composition system is very expensive and time-consuming. Therefore, the performance modeling of Web Services compsition is an important research direction of business process re-engineering.At present, most reserches on the performance analysis of Web services composition are concentrated on mathematical methods. However, the premise of analysis by mathmetical methods is to simply the execution environment of Web services composition and neglects some details about exception handling and transaction when modeling, because it is difficult to analyze them by mathematic methods. In this thesis, the researches are deployed aiming at resolving thes deficiencies. This thesis studies the simulation-based modeling and anaysis of Web services composition by formal methods, with a special focus on the following aspects: exception handling and transaction. The details of results are as follows.In this thesis, the main research target is WS-BPEL process. Therefore, this thesis firstly discusses the abstract syntax and semantics of WS-BPEL and regard that the modeling of BPEL process is devided into two parts. The first part is concentrated on the modeling of the basic control flow in BPEL. The second part is to model the execution context of BPEL process, including the behaviors of exception handling and transaction. This thesis presents a model of composite Web service, which is correponse to activity in BPEL specification.Secondly, this thesis studies in the modeling power of general stochastic Petri nets (GSPN) and the modeling methods by general stochastic Petri nets of composite Web service. Besides discussing the construction of the basic control flow, for example, AND-split, OR-split, AND-join and OR-join construct, the thesis also especially presents the modeling of interrupt event by the definition of GSPN, which is used to simulate the exception handling and transaction behavior. This thesis presents a GSPN-based algebra, used to model the control flows and Web services composition process. This algebra is expressive enough to capture the semantics of complex Web service composition.Thirdly, to better support long-running transactions, BPEL provides some special exception handling and compensation mechanisms which have complex semantics. The thesis studies that the states of activity in BPEL during BPEL process is executing and present the state frame of composite Web service. On the basis of state frame, the thesis discusses the state space of the model of activity in BPEL and the transition relation among the states. In consequence, a state transition system is presented in this thesis. It models the process of state transition and simulates the behavior of exception handling and transaction.Finally, the thesis presents the transforming methods from WS-BPEL to Petri nets and uses these results to evaluate the performance of BPEL process after the reduction.