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Automata for Unordered Trees

Abstract

International audienceWe present a framework for defining automata for unordereddata trees that is parametrized by the way in which multisets of children nodes are described. Presburger tree automata and alternatingPresburger tree automata are particular instances. We establish the usual equivalence in expressiveness of tree automata and MSO for the automata defined inour framework.We then investigate subclasses of automata for unordered treesfor which testing language equivalence is in P-time. For this we start from automata in our framework that describe multisets of childrenby finite automata, and propose two approaches of how todo this deterministically. We show that a restriction to confluent horizontal evaluation leads to polynomial-time emptiness and universality, but still suffers fromcoNP-completeness of the emptiness of binary intersections. Finally, efficient algorithms can be obtained by imposing an order of horizontal evaluation globally for all automata in the class. Depending onthe choice of the order, we obtain different classes of automata, eachof which has the same expressiveness as Counting MSO

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