Streaming ranked-tree-to-string transducers

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Streaming tree transducers with single-use restriction (STTsurs) were introduced by Alur and D'Antoni as an analyzable, executable, and expressive model for transforming unranked ordered trees in a single pass. The equivalence problem of STTsurs is decidable because their class is as expressive as the class of MSO-definable tree transformations. In this paper, we present streaming ranked-tree-to-string transducers (SRTSTs), based on STTsurs: SRTSTs are released from the single-use restriction while their input and output are restricted to ranked trees and strings, respectively. We show that the expressiveness of SRTSTs coincides with that of deterministic top-down tree transducers with regular look-ahead (yDTRs), whose equivalence problem is known to be decidable. Our proof is done by constructing equivalent transducers in both directions.

Original languageEnglish
Pages (from-to)165-187
Number of pages23
JournalTheoretical Computer Science
Publication statusPublished - 2021 May 16


  • Equivalence
  • Expressiveness
  • Ranked trees
  • Streaming transducers

ASJC Scopus subject areas

  • Theoretical Computer Science
  • Computer Science(all)


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