Message Based Transitions are available for the Begin and Message Wait event types. A Message Based Transition can be added by using the source flow object argument mapping sets.
Begin and Message Wait events can receive different sets of arguments. Each set has a name defined as the Argument set name. Within each set, the arguments can be mapped to instance variables or predefined variables. For any of these mappings, a new outgoing transition can be added to the flow object. The transition type is called Message Based Transition. Basically, you define the transition that the instance will flow through based on the received message.
There cannot be more that one outgoing message based transition for the same Argument set name.