Design And Implementation Of Workflow Engine Based On The Publish/Subscribe Mechanism

With the development of workflow technology in practice,it has become a hot topic in the field of computer science.The business rules in real-world applications can be expressed as forms which can be identified by computer,so that the business processes can be processed automatically,which improves the work efficiency a lot.Along with the wide use of workflow technology,the business process changes frequently and becomes more complicated,which raises critical requirements for high flexibility of the workflow.Traditional control-driven workflow needs to define a flow chart in advance where the execution order of the activities of the process should be known,which leads to constraints on the flexibility of the workflow.In contrast,the execution of activities is driven by the result of predecessor activities in data-driven workflow,which can lead to higher flexibility.The process of distributed execution in distributed heterogeneous environments is even more complicated and requires more flexible solutions.The publish/subscribe mechanism has become widely used in distributed systems due to the advantages of loose coupling.However,it has rarely been applied to workflow technology.Based on the publish/subscribe mechanism and the data-driven mode,a publish/subscribe-based workflow is proposed and the dedicated workflow engine system is implemented in this dissertation.This system can be applied in publish/subscribe scenarios,which can acquire high flexibility in the steps of process definition and execution.Moreover,its prospect will be more expansive in distributed systems.The main contributions of this dissertation is summarized as follows:(1)A publish/subscribe-based workflow is proposed.The definition rules of process in data-driven mode is given,regarding an activity as the key item and taking the input and output parameters into account in the description of a process.(2)Based on the data dependencies between activities,an automatic publish/subscribe-based modeling solution of workflow is proposed,which can produce data-flow chart composed of activities and provide pre-detection mechanism to detect weather the exit node is reachable or whether any loop-route exists in the process.(3)According to the standard of workflow reference model,a publish/subscribe-based workflow engine is designed and implemented.Other than the core scheduling function of workflow engine,it also provides interfaces of process definition,monitoring and management to construct a complete workflow system.Meanwhile,the problem of optimization of resource allocation in workflow scheduling is also considered.The proposed system is implemented in a distributed manner.The core functions are distributed to each activity node for parallel execution.Moreover,it also supports dynamic modification of the process during the execution process,achieving higher flexibility.(4)Extensive experiments are conducted to verify the effectiveness of the system functions and higher flexibility in the proposed workflow is showed.