sometimes an activity consists of both sequential and unordered sub-activities. the solution to this modeling issue is to divide the main activity in different parts. in figure 4 an example is illustrated, which clarifies the necessity to be able to model unordered activities. the example is taken from the requirements analysis workflow of the unified process. the main activity, “describe candidate requirements”, is divided into two parts. the first part is a sequential activity. the second part consists of four activities that do not need any sequence in order to be carried out correctly.