Workflow management systems are very useful for integrating sepa-
rately developed application systems by controlling flows of execution. For various
purposes (e.g. distribution of activities, workflow evolution, time calculation, etc.)
it is necessary to change the representation of a workflow, the structure of a work-
flow graph without changing it’s semantics. We provide an equivalence definition of
workflow graphs and introduce a set of basic transformation operations defined on
workflow graphs which keep the semantics. We show how these basic operations can
be combined to achieve complex transformations and briefly describe a prototypical
transformation tool.