RELATING TREE SERIES TRANSDUCERS AND WEIGHTED TREE AUTOMATA
Abstract
Bottom-up tree series transducers (tst) over the semiring are implemented with the help of bottom-up weighted tree automata (wta) over an extension of
. Therefore bottom-up
-weighted tree automata (
-wta) with
a distributive Ω-algebra are introduced. A
-wta is essentially a wta but uses as transition weight an operation symbol of the Ω-algebra
instead of a semiring element. The given tst is implemented with the help of a
-wta, essentially showing that
-wta are a joint generalization of tst (using IO-substitution) and wta. Then a semiring and a wta are constructed such that the wta computes a formal representation of the semantics of the
-wta. The applicability of the obtained presentation result is demonstrated by deriving a pumping lemma for deterministic finite
-wta from a known pumping lemma for deterministic finite wta. Finally, it is observed that the known decidability results for emptiness cannot be applied to obtain decidability of emptiness for finite
-wta. Thus with help of a weaker version of the derived pumping lemma, decidability of the emptiness problem for finite
-wta is shown under mild conditions on
.
This is an extended and revised version of: A. Maletti, "Relating Tree Series Transducers and Weighted Tree Automata," in Proc. 8th Int. Conf. on Developments in Language Theory, eds. C. Calude, E. Calude and M. J. Dinneen, LNCS 3340 (Springer, Heidelberg, 2004) pp. 321–333.
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