On regions and zones for event-clock automata

Event clock automata ($$\mathsf{ECA}$$ECA ) are a model for timed languages that has been introduced by Alur, Fix and Henzinger as an alternative to timed automata, with better theoretical properties (for instance, $$\mathsf{ECA}$$ECA   are determinizable while timed automata are not). In this paper, we revisit and extend the theory of $$\mathsf{ECA}$$ECA . We first prove that no finite time abstract language equivalence exists for $$\mathsf{ECA}$$ECA , thereby disproving a claim in the original work on $$\mathsf{ECA}$$ECA . This means in particular that regions do not form a time abstract bisimulation. Nevertheless, we show that regions can still be used to build a finite automaton recognizing the untimed language of an$$\mathsf{ECA}$$ECA . Then, we extend the classical notions of zones and DBMs to let them handle event clocks instead of plain clocks (as in timed automata) by introducing event zones and Event DBMs (EDBMs). We discuss algorithms to handle event zones represented as EDBMs, as well as (semi-) algorithms based on EDBMs to decide language emptiness of $$\mathsf{ECA}$$ECA .