Workflow management systems are increasingly identified as a tool that can not only integrate existing computer applications but also dynamically change existing processes in engineering and manufacturing areas as well as business areas. Since workflow transactions do not have a mechanism to guarantee consistency against failures or concurrent execution, the capability to forecast the effects of workflow transactions is very important Further, workflow modelling involves many problems that originate from application-oriented requirements as well as transaction-oriented requirements. Thus, it is necessary to represent task state dependencies that are used to define the execution order of each task to be able to express fine control requirements for engineering/manufacturing processes. This paper proposes Task Net, which is a transactional workflow model based on coloured Petri nets. First, a workflow specification language is introduced that can express task state dependency relationships such as forward, backward, and mutual exclusion among intra-task states (states of the same task) and inter-task states (states of different tasks). Then, translation procedures of a basic workflow specification and its task state dependencies into a Task Net are described. The proposed workflow language will enable the users to express both the transaction-oriented and application-oriented requirements of complex rules. The Task Net will allow simulation of the given workflow. Before executing a Task Net, tests for deadlocks and redundant task state dependencies are performed to prevent futile efforts. The proposed language, along with various analyses and simulation of Task Nets, is expected to expand the transactional workflow supports provided by current workflow systems, hence, enabling effective integration of existing computer aided (CA) applications as well as flexible definition, control and redesign of engineering and manufacturing processes.
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