Study Of Modeling Techniques Based On Petri Net And QoS Analysis Of Dynamic Workflows

Along with the rapid development of computer technology, cloud computing and economic globalization, workflow technology is currently being applied in quite diverse domains. However, the factors of change are present in some degree and form in process in almost all domains. It means that organizations or enterprises need to adjust their activities to deal with these factors in the execution of business processes. In order to adapt the increasingly fierce competition, dynamic changeable market environment and personalized user requirements, the dynamics, flexibility and adaptability of workflow systems must be improved. These characteristics not only bring to enterprises huge economic efficiency, but also provide a huge challenge to workflow models. For example, process instances are usually deviating from the pre-defined processes in runtime and loosing the control. How to handle the transition of the workflow instance in runtime, guarantee the transformed process which can not only realize the original target, but also avoid running detached and so on, become an urgent problem to be solved.The dynamic changes of workflow mainly include process changes, instance migration and workflow evolution and so on. This paper mainly focus on the study of modeling technology for dynamic workflow, as well as the transition rules of realizing workflow instance migration.Firstly, this paper proposes Place-Programmed Petri Nets (PPPN) and Transition-Programmed Petri nets (TPPN) which respectively aim at workflows constrained by resources and stochastic workflows. Based on these, we consider places which have local storage described by variables (or attributes), and propose the definition of Programmed Petri Nets. This paper further describes its transition firing rule, and proves equivalence between PPPN and colored Petri nets. After that, we propose the definition of Programmed Workflow Nets (PWN) by modifying the definition of PPN, and deeply analyze dynamic mechanism of PWN.Secondly, we propose the definition of rewriting nets based on PWN and its rewriting rules. The models and rules of rewriting nets based on PWN can realize all operations of various changing modes, and can alter the support characteristics, which can compares existing process management technology from the view of systems, of the changes of control flows. There are two ways to change the business processes of rewriting nets based on PWN. One is to change the programming functions of PWN, the other is to change the structure of current business process in order to improve the performance of the system, or to add, delete and update service in order to adapt environments and the change of business requirements. For the sake of dealing the transition of instances in runtime, we propose some definitions such as conservative state, and prove some properties.Lastly, we introduce stochastic network calculus on account of the stochastic workflows including dynamic services composition. We apply arrival curves and service curves to analyze the delay bounds and backlog bounds of services composition based on communication network. It can be concluded the QoS evaluation of dynamic services composition under stochastic service guarantee. Meanwhile, we analyze the performance of two scenarios through instance simulation.