This paper offers a critical analysis of the popular control-flow-oriented workflow modeling paradigm and argues that time is not just an additional property specified on the top of control flows as it is commonly done in commercial and research workflow models. It also explains why this way of time modeling can easily lead to an inability to properly specify temporal constraints and verify their consistency. The paper proposes a two-level workflow modeling where the control-flow level is used for modeling of control flows, monitoring of workflow execution and reasoning about the order of tasks while the operational level is used for more precise time modelling and verification of temporal constraints.
Marjanovic, Olivera, "Methodological Considerations for Time Modeling inWorkflows" (2001). ACIS 2001 Proceedings. Paper 42.