  Event-clock automata (ECA) are a well-known semantic subclass of timed
automata (TA) which enjoy admirable theoretical properties, e.g.,
determinizability, and are practically useful to capture timed specifications.
However, unlike for timed automata, there exist no implementations for checking
non-emptiness of event-clock automata. As ECAs contain special prophecy clocks
that guess and maintain the time to the next occurrence of specific events,
they cannot be seen as a syntactic subclass of TA. Therefore, implementations
for TA cannot be directly used for ECAs, and moreover the translation of an ECA
to a semantically equivalent TA is expensive. Another reason for the lack of
ECA implementations is the difficulty in adapting zone-based algorithms,
critical in the timed automata setting, to the event-clock automata setting.
This difficulty was studied by Geeraerts et al. in 2011, where the authors
proposed a zone enumeration procedure that uses zone extrapolations for
finiteness. In this article, we propose a different zone-based algorithm to
solve the reachability problem for event-clock automata, using simulations for
finiteness. A surprising consequence of our result is that for event-predicting
automata, the subclass of event-clock automata that only use prophecy clocks,
we obtain finiteness even without any simulations. For general event-clock
automata, our new algorithm exploits the G-simulation framework, which is the
coarsest known simulation relation in timed automata literature, and has been
recently used for advances in other extensions of timed automata.
