Mixed Initiative Realizability Problem Resolution Using UML Composite States

Realizability problems may emerge when specifications of complex distributed reactive systems are mapped to local distributed designs that may contain undesired behaviours, sometimes termed as implied scenarios. In this paper, we focus on resolving one of these realizability problems named as mixed initiative that occurs when independent and concurrent entities take uncoordinated initiatives autonomously. The mixed initiative problem is unavoidable in the execution of some distributed reactive systems and can normally not be prevented. Mixed initiative resolution guidelines have been proposed in the past that use UML activity diagrams and/or additional transitions in UML state machines. The novelty in our approach lies in the use of UML composite states for resolving the mixed initiative problem. However, UML does not have well-defined guidelines on serialization/unfolding of composite states. This paper, therefore, first proposes guidelines on how to serialize/unfold a UML composite state and then how to use it for addressing mixed initiative realizability problem using a case study named Call Centre.