Automata for Unordered Trees
Abstract
We present a framework for defining automata for unordered
data trees that is parametrized by the way in which multisets of
children nodes are described. Presburger tree automata and alternating
Presburger tree automata are particular instances. We establish the usual equivalence
in expressiveness of tree automata and MSO for the automata defined in
our framework.
We then investigate subclasses of automata for unordered trees
for which testing language equivalence is in P-time. For this we start from
automata in our framework that describe multisets of children
by finite automata, and propose two approaches of how to
do this deterministically. We show that a restriction to confluent horizontal evaluation leads to
polynomial-time emptiness and universality, but still suffers from
coNP-completeness of the emptiness of binary intersections. Finally,
efficient algorithms can be obtained by imposing an order of horizontal
evaluation globally for all automata in the class. Depending on
the choice of the order, we obtain different classes of automata, each
of which has the same expressiveness as Counting MSO.
Origin : Files produced by the author(s)
Loading...