Research On Dynamic Evolution Of Web Service Compositions

The Internet is now evolving from an information sharing and exchanging network to a resource sharing and integrating platform. Conforming to this trend, there emerges Service Computing as a computing paradigm. In the application mode of Services Computing, Web service composition is an effective means to achieve resource integration. Therefore, Web service composition is becoming hotspot of the software technique research. Web service composition runs on the open Internet platform, thus it needs the ability to evolve dynamically in order to adapt to the ever-changing user requirements and system environments. However, current standards, methods and techniques on Web service and Web service composition are insufficient to meet the needs. The dynamic evolution of a Web service composition is still confronted with many technical challenges. The challenges include the following aspects, (I) the static evolution of a Web service composition:how to guarantee that in the evolution process the correctness especially the data flow correctness of a Web service composition is not violated; (II) the dynamic evolution of a service orchestration:how to update the process definition of a service orchestration at run-time stage such that the changes happened at the process definition level can be dynamically propagated to the running service orchestration instances; (III) the dynamic evolution of a service choreography:how to cooperate the dynamic evolution of service orchestrations effectively without any central control while the dynamic evolution of a service choreography could be realized. The following efforts are presented in this dissertation to cope with these challenges:1. After the analysis of the technical requirements for the dynamic evolution of Web service compositions, a process-aware-based means to the dynamic evolution of Web service compositions is proposed. Based on this technical means, a unified conceptual framework of the dynamic evolution of Web service compositions is presented. This conceptual framework can support the dynamic evolution of Web service compositions not only from different ranges (i.e., service orchestrations and service choreographies), but also from different levels (process definition level and process instance level).2. By studying the preservation of data flow correctness in the static evolution of. a Web service composition, a set of evolution operations and corresponding usage guidelines are put forward to help the software developers adapt the Web service composition correctly. The particularity of this approach lies in two aspects. (I) The approach is an incremental solution, that is, it only checks the parts that have the possibility to be affected; in this way, the approach can determine whether or not the evolution operations will undermine the data flow correctness of a Web service composition. (II) This is a correctness-by-construction approach, that is, when the evolution operations affect the data flow correctness of the Web service composition, further evolution operations will be provided to the software developers to remedy the problems.3. A flexible instance-migration-based approach to the dynamic evolution of service orchestrations is presented, and the approach can dynamically propagate the changes happening at the level of orchestration process definition to the level of running orchestration instances. With a view to interpret the approach, first, the validity of orchestration instance migration is defined. Then, a migratability criterion is proposed, which can guarantee the validity of orchestration instance migration. In the end, the algorithm of the migratability criterion is put forward. Compared with the existing migratability checking approaches, this approach is more flexible in that it not only guarantees the validity of orchestration instance migration, but also allows more orchestration instances to migrate to the orchestration process after evolution.4. Considering the characteristics of the choreography-based Web service composition methodology, an approach to the dynamic evolution of service choreographies, which is based on the dynamic co-evolution of service orchestrations, is presented. This approach is implemented as a choreography evolution protocol, which can effectively support the propagation of service choreographies and the dynamic co-evolution of service orchestrations. In this approach, to guarantee the transactional property of the choreography evolution, the dynamic evolution of a service choreography would be feasible if and only if all service orchestrations affected by the choreography evolution can evolve simultaneously.5. A supporting system for the dynamic evolution of Web service composition is designed and partially implemented. This supporting system is based on the widely used JBoss jBPM platform, and the platform provides a graphical user interface which can support the development and execution of Web service compositions. The functions of the JBoss jBPM platform are extended so that the whole system can support the static evolution of the Web service compositions, the dynamic evolution of a single service orchestration as well as the dynamic co-evolution of several service orchestrations. In addition, on the basis of this supporting system, a travel agency Web service composition, which can evolve dynamically, is designed as a case study to demonstrate the feasibility and validity of the techniques for the dynamic evolution of Web service compositions proposed in this dissertation.