Preemptive Time Petri Nets are obtained by extending Time Petri Nets with an additional mechanism of resource assignment which makes the progress of timed transitions be dependent on the availability of a set of preemptable resources, and with the capability to make transition times and priorities be dependent on the marking.

The combination of these capabilities supports description and verification of flexible real time systems running under preemptive scheduling, with periodic, sporadic and one shot processes, with non-deterministic execution times, with semaphore synchronizations and precedence relations deriving from internal task sequenzialization and from interprocess communication.

The expressive capabilities of the model and the type of results that can be derived through symbolic enumeration of its dense-timed state space are illustrated with reference to a flexible system mixing dynamic acceptance and performance polymorphism.