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  • 1.
    Bensch, Suna
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Bordihn, Henning
    Institut für Informatik, Universität Potsdam.
    Holzer, Markus
    Institut für Informatik, Universität Giessen.
    Kutrib, Martin
    Institut für Informatik, Universität Giessen.
    On input-revolving deterministic and nondeterministic finite automata2009In: Information and Computation, ISSN 0890-5401, E-ISSN 1090-2651, Vol. 207, p. 1140-1155Article in journal (Refereed)
    Abstract [en]

    We introduce and investigate input-revolving finite automata, which are (nondeterministic) finite state automata with additional ability to shift the remaining part of the input. Three different modes of shifting are considered, namely revolving to the left, revolving to the right, and circular-interchanging. We investigate the computational capacities of these three types of automata and their deterministic variants, comparing any of the six classes of automata with each other and with further classes of well-known automata. In particular, it is shown that nondeterminism is better than determinism, that is, for all three modes of shifting there is a language accepted by the nondeterministic model but not accepted by any determinstic automaton of the same type. Concerning the closure properties most of the deterministic language families studied are not closed under standard operations. For example, we show that the family of languages accepted by deterministic right-revolving finite automata is an anti-AFL which is not closed under reversal and intersection.

  • 2.
    Bjorklund, Johanna
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Fernau, Henning
    Kasprzik, Anna
    Polynomial inference of universal automata from membership and equivalence queries2016In: Information and Computation, ISSN 0890-5401, E-ISSN 1090-2651, Vol. 246, p. 3-19Article in journal (Refereed)
    Abstract [en]

    A MAT learning algorithm is presented that infers the universal automaton (UA) for a regular target language, using a polynomial number of queries with respect to that automaton. The UA is one of several canonical characterizations for regular languages. Our learner is based on the concept of an observation table, which seems to be particularly fitting for this computational model, and the necessary definitions are adapted from the literature to the case of UA. 

  • 3.
    Blum, Johannes
    et al.
    University of Würzburg.
    Drewes, Frank
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Language Theoretic Properties of Regular DAG Languages2019In: Information and Computation, ISSN 0890-5401, E-ISSN 1090-2651, Vol. 265, p. 78p. 57-76Article in journal (Refereed)
    Abstract [en]

    We study sets of directed acyclic graphs, called regular DAG languages, which are accepted by a recently introduced type of DAG automata motivated by current developments in natural language processing. We prove (or disprove) closure properties, establish pumping lemmata, characterize finite regular DAG languages, and show that "unfolding" turns regular DAG languages into regular tree languages, which implies a linear growth property and the regularity of the path languages of regular DAG languages. Further, we give polynomial decision algorithms for the emptiness and finiteness problems, and show that deterministic DAG automata can be minimized and tested for equivalence in polynomial time.

  • 4.
    Drewes, Frank
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Engelfriet, Joost
    Leiden Institute of Advanced Computer Science.
    The Generative Power of Delegation Networks2015In: Information and Computation, ISSN 0890-5401, E-ISSN 1090-2651, Vol. 245, p. 78p. 213-258Article in journal (Refereed)
    Abstract [en]

    A device that generates trees over a ranked alphabet, together with an interpretation of the symbols in that alphabet as functions or relations on some domain, generates subsets of that domain. This concept of tree-based generators is well known and essentially already present in the seminal paper by Mezei and Wright from 1967. A delegation network is a system consisting of a finite set of such generators that can "delegate" parts of the generation process to each other. It can be viewed as consisting of an (extended) IO context-free tree grammar and an interpretation. We investigate the language-theoretic properties of these systems and establish several characterizations of the generated languages. In particular, we obtain results in the style of Mezei and Wright. We also study the hierarchy of tree language classes obtained by iterating the concept of delegation, and show that this hierarchy is properly contained in the closure of the regular tree languages under nondeterministic macro tree transductions, but not contained in the IO-hierarchy.

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