Process pattern is an emerging approach for process reuse. Representing process models based on process patterns to explicit process solutions and factor recurrent process constituents is useful for process understanding as well as process modeling. This subject, however, is still a challenge for the software process technology community. In this paper, we present a UML-based process meta-model that allows explicit representation of process patterns in process models. The novel of our proposition is to enable the application of different process knowledge kinds not only for building but also for improving process models.