| Abstrakt: |
We compare various modes of firing transitions in Petri nets and investigate classes of languages specified by them. We define languages through steps, (i. e., sets of transitions), maximal steps, multi-steps, (i. e., multisets of transitions), and maximal multi-steps of transitions in Petri nets. However, by considering labeled transitions, we do this in a different manner than in [Burk 81a, Burk 83]. Namely, we allow only sets and multisets of transitions to form a (multi-)step, if they all share the same label. In a sequence of (multi-)steps, each of them contributes its label once to the generated word. Through different firing modes that allow multiple use of transitions in a single multi-step, we obtain a hierarchy of families of languages. Except for the maximal multi-steps all classes can be simulated by sequential firing of transitions. [ABSTRACT FROM AUTHOR] |
