II.3.3. T-timed Petri Nets

For transition-timed PNs (T-timed PNs), time durations can be assigned to the transitions; tokens are meant to spend that time as reserved in the input places of the corresponding transitions. In simulation, all the transitions that can fire due to the current marking are fired at the same time. For conflicting transitions, priorities or probabilities allow the choice of the transition(s) to fire. A transition can fire several times, in accordance with the marking of its input places and, from a theoretical point of view, an infinitesimal delay is considered to separate any two successive firings. After a transition fires, the enabling condition is tested for all the transitions of the net.

For the time durations assigned to the transitions, appropriate functions can be used to generate random sequences corresponding to probability distributions with positive support. When a transition is waiting to fire (i.e. during the period when its input places contain reserved tokens) the reserved tokens are graphically removed from the input places, but the computation procedures of the performance indices consider them as remaining in those places (in full accordance with the theoretic approach).

The Diary facility opens a new window that displays (dynamically) the instant(s) when the next fireable transition(s) is (are) to fire.

The Scope facility opens a new figure window that displays (dynamically) the evolution of the selected performance indices. The final value of the global index shown by the Scope is identical to that displayed on request, at the end of simulation, when the user explores the Performance menu.