When Is a Bottom-Up Deterministic Tree Translation Top-Down Deterministic?

Authors Sebastian Maneth, Helmut Seidl

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Sebastian Maneth
  • Universität Bremen, Germany
Helmut Seidl
  • TU München, Germany

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Sebastian Maneth and Helmut Seidl. When Is a Bottom-Up Deterministic Tree Translation Top-Down Deterministic?. In 47th International Colloquium on Automata, Languages, and Programming (ICALP 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 168, pp. 134:1-134:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)


We consider two natural subclasses of deterministic top-down tree-to-tree transducers, namely, linear and uniform-copying transducers. For both classes we show that it is decidable whether the translation of a transducer with look-ahead can be realized by a transducer without look-ahead. The transducers constructed in this way, may still make use of inspection, i.e., have an additional tree automaton restricting the domain. We provide a second procedure which decides whether inspection can be removed and if so, constructs an equivalent transducer without inspection. The construction relies on a fixpoint algorithm that determines inspection requirements and on dedicated earliest normal forms for linear as well as uniform-copying transducers which can be constructed in polynomial time. As a consequence, equivalence of these transducers can be decided in polynomial time. Applying these results to deterministic bottom-up transducers, we obtain that it is decidable whether or not their translations can be realized by deterministic uniform-copying top-down transducers without look-ahead (but with inspection) - or without both look-ahead and inspection.

Subject Classification

ACM Subject Classification
  • Theory of computation → Models of computation
  • Theory of computation → Formal languages and automata theory
  • Top-Down Tree Transducers
  • Earliest Transformation
  • Linear Transducers
  • Uniform-copying Transucers
  • Removal of Look-ahead
  • Removal of Inspection


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