Modeling Urgency in Timed Systems

{ States are associated with time progress conditions specifying how time can advance. Time can progress at a state by t only if all the intermediate states reached satisfy the associated time progress condition. { At transitions, clock values can be tested and modi ed. This is usually done by associating with transitions guards (conditions on clocks) and assignments. If a guard is true from an automaton state and a given clock valuation, the corresponding transition can be executed by modifying clocks as speci ed by the corresponding assignment.