A method to transform graphic control flow models into separable forms is proposed under the true concurrency equivalence notion to evolve process models during the workflow modeling. The separable form means that sequential and concurrent structures can be handled separately. Free choice WF-nets are used as control flow models

and fully concurrent bis-imulation is chosen as the true concurrency equivalent notion. Then the sufficient conditions that two safe nets are fully concurrent bisimilar are given. A partial unfolding algorithm is proposed for WF-nets to obtain their separable forms based on the net unfolding of Petri nets. The equivalence of a partial unfolding net and its original WF-net is ensured by proving that both the models satisfy the sufficient conditions of fully concurrent bisimilation. Comparisons with existing methods show that the proposed transformation method could preserve the concurrency level with less steps

and hence facilitates the evolvement of process models.