Languages of Petri Nets

If the transitions of a Petri net are associated with the letters of some alphabet, then the firing sequences correspond to words over that alphabet. The set of firing sequences is clearly prefix-closed, but if a notion of final state (in addition to the initial marking) is also introduced, some interesting, not necessarily prefixclosed, sets of accepted words (i.e., languages) can be investigated. In this chapter, the languages which arise through such an extension are characterised.