A protocol transition (transition as specialized in the ProtocolStateMachines package) specifies a legal transition for an operation. Transitions of protocol state machines have the following information: a pre condition (guard), on trigger, and a post condition. Every protocol transition is associated to zero or one operation (referred BehavioralFeature) that belongs to the context classifier of the protocol state machine. The protocol transition specifies that the associated (referred) operation can be called for an instance in the origin state under the initial condition (guard), and that at the end of the transition, the destination state will be reached under the final condition (post).