Disadvantages
- Less Expressiveness: OPNA problem
Let a total state of a SP-DEVS model be passive if ; otherwise, it be active.
One of known SP-DEVS's limitation is a phenomenon that "once an SP-DEVS model becomes passive, it never returns to become active (OPNA)". This phenomenon was found first at although it was originally called ODNR ("once it dies, it never returns."). The reason why this one happens is because of the restriction (3) above in which no input event can change the schedule so the passive state can not be awaken into the active state.
For example, the toaster models drawn in Fig. 3(b) are not SP-DEVS because the total state associated with "idle" (I), is passive but it moves to an active state, "toast" (T) whose toating time is 20 seconds or 40 seconds. Actually, the model shown in Fig. 3(b) is FD-DEVS.
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