Research On Migrating Workflow Service Method Supporting Exception Handling

Migrating workflow is a new development direction of the workflow technology recently. The migrating workflow management system contains three elements: migrating workflow engine,migrating instance and workplace. The migrating engine takes charge of the workflow process's definition,migrating instance's generation and the coordination of the migrating instances. The migrating instance is constructed by the paradigm of the mobile Agent and is the execution entity of the migrating workflow. It takes the task specification and migrates among the workplaces which are defined by the itinerary graph continuously. It finishes one or more tasks making use of the workplace service locally. The workplace contains the anchorage server and work-station network. It provides the run-time service and workflow service for the migrating instance.In migrating workflow management system, the service which the workplace provides is the precondition of finishing the tasks which the migrating instance submits. The exceptions appeared in the service process for the migrating instance will prevent the migrating workflow from executing properly and exactly. So, migrating workflow management system must handle the exceptions appeared on the workplace in order to keep the migrating workflow's execution proper and exact. The workplace exceptions are divided into physical failure exceptions and logical failure exceptions, the former means workplace machine fails,network breaks down etc. Meanwhile, the latter one means that the workflow services provided by the workplace change,the service can not execute according to the plans or the service can not get the anticipated results. This thesis studied on the handling of the logical failure exception, that is, how to provide the migrating workflow service supporting the exception handling.Firstly, this thesis analyzes the characteristics of the service exception handling according to the characteristics of the migrating workflow service.The concept and model of the compensation in migrating workflow service are gave out based on the characteristics of service and its exception handling. Then, for the autonomous characteristic of the service provided by the workplace, a migrating workflow service model supporting exception handling is proposed based on the Case-Based Reasoning. In this model, the case is organized by the workstation service and is used to manage and reuse the service knowledge and compensation knowledge of the workplace.The service case is used to manage and organize the workstation service in order to implement the autonomy of the workplace's service, and the compensation case is used to set the local compensation path and handle the workflow service exception. The model combines the exception handling method with the service method. Exception handling takes the local service knowledge and the service exceptions' context into account and makes use of the compensation knowledge in the compensation case to handle the exception detected in order to keep the migrating workflow service process integrated and exact,recovering the failure tasks. Finally, the workplace workflow service framework is designed based on the proposed workflow service model, and the workflow service process based on the service case and the service exception handling process based on the compensation case are gave out.Based on the proposed workflow service method, the case that the bookstore workflow service system providing the books' distribution service for the migrating instance shows the proposed service method can keep the local service's autonomous and enhance the migrating workflow management system's ability to handle the exceptions. The future research will focus on the case matching based on the ontology and active service provided by the workplace for the migrating instance.