Look-Ahead Removal for Top-Down Tree Transducers
Abstract
Top-down tree transducers are a convenient formalism for describing tree transformations. They can be equipped with regular look-ahead, which allows them to inspect a subtree before processing it. In certain cases, such a look-ahead can be avoided and the transformation can be realized by a transducer without look-ahead. Removing the look-ahead from a transducer, if possible, is technically highly challenging. For a restricted class of transducers with look-ahead, namely those that are total, deterministic, ultralinear, and bounded erasing, we present an algorithm that, for a given transducer from that class, (1) decides whether it is equivalent to a total deterministic transducer without look-ahead, and (2) constructs such a transducer if the answer is positive. For the whole class of total deterministic transducers with look-ahead we present a similar algorithm, which assumes that a so-called difference bound is known for the given transducer. The designer of a transducer can usually also determine a difference bound for it.
Keywords
Cite
@article{arxiv.1311.2400,
title = {Look-Ahead Removal for Top-Down Tree Transducers},
author = {Joost Engelfriet and Sebastian Maneth and Helmut Seidl},
journal= {arXiv preprint arXiv:1311.2400},
year = {2015}
}
Comments
57 pages, to appear in TCS