Nested Timed Automata

This paper proposes a new timed model named nested timed automata (NeTAs). An NeTA is a pushdown system whose stack symbols are timed automata (TAs). It either behaves as the top TA in the stack, or switches from one TA to another by pushing, popping, or changing the top TA of the stack. Different from existing component-based context-switch models such as recursive timed automata and timed recursive state machines, when time passage happens, all clocks of TAs in the stack elapse uniformly. We show that the safety property of NeTAs is decidable by encoding NeTAs to the dense timed pushdown automata. NeTAs provide a natural way to analyze the recursive behaviors of component-based timed systems with structure retained. We illustrate this advantage by the deadline analysis of nested interrupts.