Dense-Timed Pushdown Automata

We propose a model that captures the behavior of real-time recursive systems. To that end, we introduce dense-timed pushdown automata that extend the classical models of pushdown automata and timed automata, in the sense that the automaton operates on a finite set of real-valued clocks, and each symbol in the stack is equipped with a real-valued clock representing its "age". The model induces a transition system that is infinite in two dimensions, namely it gives rise to a stack with an unbounded number of symbols each of which with a real-valued clock. The main contribution of the paper is an EXPTIME-complete algorithm for solving the reachability problem for dense-timed pushdown automata.