Shape Preserving Tree Transducers

TL;DR

This paper proves that shape preservation is decidable for various classes of tree transducers and introduces a normal form for shape-preserving transducers, where each input node corresponds to exactly one output node.

Contribution

It establishes decidability of shape preservation for top-down, bottom-up, and macro tree transducers and presents a normal form for such transducers.

Findings

Shape preservation is decidable for top-down and bottom-up tree transducers.

Shape-preserving transducers can be transformed into a normal form with one output node per input node.

The normal form simplifies analysis and implementation of shape-preserving transducers.

Abstract

It is shown that shape preservation is decidable for top-down tree transducers, bottom-up tree transducers, and for compositions of total deterministic macro tree transducers. Moreover, if a transducer is shape preserving, then it can be brought into a particular normal form, where every input node creates exactly one output node.