Pushdown automaton

About: Pushdown automaton is a research topic. Over the lifetime, 1868 publications have been published within this topic receiving 35399 citations.

Systems and methods for determining the N-best strings

Abstract: Systems and methods for identifying the N-best strings of a weighted automaton. A potential for each state of an input automaton to a set of destination states of the input automaton is first determined. Then, the N-best paths are found in the result of an on-the-fly determinization of the input automaton. Only the portion of the input automaton needed to identify the N-best paths is determinized. As the input automaton is determinized, a potential for each new state of the partially determinized automaton is determined and is used in identifying the N-best paths of the determinized automaton, which correspond exactly to the N-best strings of the input automaton.

On the equivalence of two-way pushdown automata and counter machines over bounded languages

Abstract: It is known that two-way pushdown automata are more powerful than two-way counter machines. The result is also true for the case when the pushdown store and counter are reversal-bounded. In contrast, we show that two-way reversal-bounded push-down automata over bounded languages (i.e., subsets of for some distinct symbols a1,…, ak) are equivalent to two-way reversal-bounded counter machines. We also show that, unlike the unbounded input case, two-way reversal-bounded pushdown automata over bounded languages have decidable emptiness, equivalence and containment problems.

Descriptional Complexity of Input-Driven Pushdown Automata

Abstract: It is known that a nondeterministic input-driven pushdown automaton (IDPDA) can be determinized. Alur and Madhusudan (“Adding nesting structure to words”, J.ACM 56(3), 2009) showed that a deterministic IDPDA simulating a nondeterministic IDPDA with n states and stack symbols may need, in the worst case, \(2^{\Omega(n^2)}\) states. In their construction, the equivalent deterministic IDPDA does, in fact, not need to use the stack. This paper considers the size blow-up of determinization in more detail, and gives a lower bound construction, that is tight within a multiplicative constant, with respect to the size of the nondeterministic automaton both for the number of states and the number of stack symbols. The paper also surveys the recent results on operational state complexity of IDPDAs, and on the cost of converting a nondeterministic automaton to an unambiguous one, and an unambiguous automaton to a deterministic one.

The Diagonal Problem for Higher-Order Recursion Schemes is Decidable

Abstract: A non-deterministic recursion scheme recognizes a language of fi-nite trees. This very expressive model can simulate, among others, higher-order pushdown automata with collapse. We show decidability of the diagonal problem for schemes. This result has several interesting consequences. In particular, it gives an algorithm that computes the downward closure of languages of words recognized by schemes. In turn, this has immediate application to separability problems and reachability analysis of concurrent systems.Categories and Subject Descriptors 500 [Theory of computation]: Grammars and context-free languages; 500 [Theory of computation]: Tree languages; 500 [Theory of computation]: Regular languages

Impartiality and Anticipation for Monitoring of Visibly Context-Free Properties

Abstract: We study monitoring of visibly context-free properties. These properties reflect the common concept of nesting which arises naturally in software systems. They can be expressed e.g. in the temporal logic CaRet which extends LTL by means of matching calls and returns. The future fragment of CaRet enables us to give a direct unfolding-based automaton construction, similar to LTL. We provide a four-valued, impartial semantics on finite words which is particularly suitable for monitoring. This allows us to synthesize monitors in terms of deterministic push-down Mealy machines. To go beyond impartiality, we develop a construction for anticipatory monitors from visibly push-down ω-automata by utilizing a decision procedure for emptiness.