Pushdown automaton

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

Incrementally-Updatable Stream Processors for XPath Queries based on Merging Automata via Ordered Hash-keys

Abstract: Various kinds of data such as news articles and sensor data are generated continuously in the form of XML data on the network. The processing systems (e.g., systems for selective dissemination of information and notification) must evaluate many filters for every XML data. Therefore, Gupta and Suciu proposed an automaton called the XPush machine, which can efficiently evaluate a large number of XPath filters, each with many predicates, on a stream of XML documents. The XPush machine is constructed by creating an AFA (Alternating Finite Automaton) for each filter, and then transforming the set of AFAs into a single DPDA (Deterministic PushDown Automaton). Since the XPush machine cannot be partially updated inherently, however, addition of a single filter necessitates recalculation (i.e., reconstruction) of the XPush machine as a whole. In other words, the cost of updating an automaton depends on the total number of AFAs (or filters). In this paper, we propose and evaluate an integrated XPush machine, which enables incremental update by constructing the whole machine from a set of sub-XPush machines. The evaluation result positively demonstrates that efficient partial exchange of the AFAs is possible without significantly affecting all of the state transition tables.

Random generation and approximate counting of ambiguously described combinatorial structures

Abstract: This paper concerns the uniform random generation and the approximate counting of combinatorial structures admitting an ambiguous description. We propose a general framework to study the complexity of these problems and present some applications to specific classes of languages. In particular, we give a uniform random generation algorithm for finitely ambiguous context-free languages of the same time complexity of the best known algorithm for the unambiguous case. Other applications include a polynomial time uniform random generator and approximation scheme for the census function of (i) languages recognized in polynomial time by one-way nondeterministic auxiliary pushdown automata of polynomial ambiguity and (ii) polynomially ambiguous rational trace languages.

Nested timed automata

Abstract: This paper proposes a new timed model named nested timed automata (NeTAs). A 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.

Brzozowski Algorithm Is Generically Super-Polynomial for Deterministic Automata

Abstract: We study the number of states of the minimal automaton of the mirror of a rational language recognized by a random deterministic automaton with n states. We prove that, for any d > 0, the probability that this number of states is greater than n d tends to 1 as n tends to infinity. As a consequence, the generic and average complexities of Brzozowski minimization algorithm are super-polynomial for the uniform distribution on deterministic automata.