效绵鼎 Pushdown Automata The PDA is an automaton equivalent to the CFG in language-defining power. ■ Only the nondeterministic PDA defines all the CFL's. ■ But the deterministic version models parsers. Most programming languages have deterministic PDA's. 2Pushdown Automata ◼ The PDA is an automaton equivalent to the CFG in language-defining power. ◼ Only the nondeterministic PDA defines all the CFL’s. ◼ But the deterministic version models parsers.  Most programming languages have deterministic PDA’s. 2