Workflow Patterns: On the Expressive Power of (Petri-net-based) Workflow Languages

Contemporary workflow management systems are driven by explicit process models, i.e., a completely specified workflow design is required in order to enact a given workflow process. Creating a workflow design is a complicated time-consuming process which is often hampered by the limitations of the workflow language being used. To identify the differences between the various languages, we have collected a fairly complete set of workflow patterns. Based on these patterns we have evaluated 15 workflow products and detected considerable differences in expressive power. Languages based on Petri nets perform better when it comes to state-based workflow patterns. However, some patterns (e.g. involving multiple instances, complex synchronizations or non-local withdrawals) are not easy to map onto (high-level) Petri nets. These patterns pose interesting modeling problems and are used for developing the Petri-net-based language YAWL (Yet Another Workflow Language).