Research On Agent-based Grid Workflow Technology

More and more powerful computing and collaborative Grid applications that require tremendous resources are constructed as the Grid researches and Grid infrastructure greatly advance. Many applications are more and more complicated, and they are constrained by temporal, spatial and resource relationship. Grid workflow can conveniently construct, execute, manage and monitor grid applications, and automate grid applications with great efficiency. Due to the dynamism, distribution, heterogeneity and autonomy of grid applications, conventional workflow technology can't effectively solve the relative problems of grid environment. The thesis is based on the application project:"ShanghaiGrid". Integrated with agent technology, the thesis mainly studies grid workflow architecture, model construction, workflow optimization and mapping mechanism. The detail is as following:1. Grid workflow architecture. The four-layer architecture contains user layer, engine layer, agent layer and application broker layer. Based on the architecture, the system is composed of some functional components, such as the distributed workflow enactment system, the component-based modeling environment, the workflow console, the multi-agent supporting platform and the middleware of external application brokers. The architecture complying with the standard of WFMC and GCC is open and extensible. In the thesis, we lay emphasis on the middleware of external application brokers and the multi-agent supporting platform. The former component is used by the system to invoke heterogeneous external applications transparently. The later component provides robust supports for the system to work properly. We also simply present considerations about fault tolerance in the system.2. Grid workflow model construction. Based on the multi-agent supporting platform and AI planning technology, we propose Plan generating algorithm and Plan merging algorithm to solve the automatic construction problem for complicated workflow models. By giving a demonstration"Online conference arrangement for the domestic conferences", we show further the feasibility and superiority of the automatic construction of workflow model based on AI planning technology.3. Optimization of Grid workflow. Based on the multi-agent supporting platform, we adopt Genetic algorithms (GA) to solve the service selection problem of grid workflow, thereby realizing grid workflow optimization. We present our GA module in detail, and analyze the simulation process by giving a demonstration"Travel arrangement composite service". The final result demonstrates that the global optimization solution can be gotten quickly and efficiently by use of Genetic algorithms. It also shows the feasibility and superiority of GA method used in service selection domain. Although the thesis focuses on the cost-driven service selection, we can expand it easily to realize multi-goal driven optimization of grid workflow.4. Mapping mechanism of grid workflow. Given the dynamic nature of the Grid environment, it is more suitable for users to define workflow applications in the abstract model. Based on the multi-agent supporting platform, we give definitions of three types of grid workflow: abstract workflow (AW), concrete workflow (CW) and executable workflow (EW). We prove the rationality of such definitions. Utilization of three workflow types further liberates model designers from sophisticated system details. It also increases the reusability of domain-specific models and improves the fault tolerance of the system. Based on the BDI definitions of all agents in the system and Contract Net Protocol (CNP) as negotiation protocol among those agents, we propose AW2CW mapping algorithm and CW2EW mapping algorithm to implement service-oriented workflow mapping efficiently. By giving a demonstration"Online conference arrangement for the international conferences", we show further the feasibility and superiority of the CNP method used in grid workflow mapping process.5. Grid workflow prototype and related application. Based on the researches that we have done and the demands of"ShanghaiGrid Workflow System", we have developed a prototype. In consideration of integrality, we also present other researches, which have been implemented or being on in the system, i.e. ECA-based grid workflow, Distributed workflow enactment system. Finally, by giving an application of a medical image processing workflow, we illustrate the collaborations among the modeling tool, the simple workflow console and the workflow engine service.