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Deterministic Automata on Unranked Trees Thomas, Wolfgang Christau, Julien Löding, Christof Automata unranked trees parikh automata We investigate bottom-up and top-down deterministic automata on unranked trees. We show that for an appropriate definition of bottom-up deterministic automata it is possible to minimize the number of states efficiently and to obtain a unique canonical representative of the accepted tree language. For top-down deterministic automata it is well known that they are less expressive than the non-deterministic ones. By generalizing a corresponding proof from the theory of ranked tree automata we show that it is decidable whether a given regular language of unranked trees can be recognized by a top-down deterministic automaton. The standard deterministic top-down model is slightly weaker than the model we use, where at each node the automaton can scan the sequence of the labels of its successors before deciding its next move. Schloss Dagstuhl – Leibniz-Zentrum für Informatik Wolfgang Thomas and Julien Christau and Christof Löding 2005 Is Part Of Dagstuhl Seminar Proceedings, Volume 5061, Foundations of Semistructured Data (2005) InProceedings Text doc-type:ResearchArticle publishedVersion application/pdf doi:10.4230/DagSemProc.05061.3 urn:nbn:de:0030-drops-2281 https://drops.dagstuhl.de/entities/document/10.4230/DagSemProc.05061.3 eng https://creativecommons.org/licenses/by/4.0/legalcode