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Computing Simulations over Tree Automata (Efficient Techniques for Reducing Tree Automata)

Summary: Computing Simulations over Tree Automata
(Efficient Techniques for Reducing Tree Automata)
Parosh A. Abdulla1, Ahmed Bouajjani2, LukŽas HolŽik3, Lisa Kaati1, and TomŽas Vojnar3
1 University of Uppsala, Sweden, email: {parosh,lisa.kaati}@it.uu.se
2 LIAFA, University Paris 7, France, email: abou@liafa.jussieu.fr
3 FIT, Brno University of Technology, Czech Rep., email: {holik,vojnar}@fit.vutbr.cz
Abstract. We address the problem of computing simulation relations over tree
automata. In particular, we consider downward and upward simulations on tree
automata, which are, loosely speaking, analogous to forward and backward rela-
tions over word automata. We provide simple and efficient algorithms for com-
puting these relations based on a reduction to the problem of computing simu-
lations on labelled transition systems. Furthermore, we show that downward and
upward relations can be combined to get relations compatible with the tree lan-
guage equivalence, which can subsequently be used for an efficient size reduction
of nondeterministic tree automata. This is of a very high interest, for instance, for
symbolic verification methods such as regular model checking, which use tree
automata to represent infinite sets of reachable configurations. We provide ex-
perimental results showing the efficiency of our algorithms on examples of tree
automata taken from regular model checking computations.
1 Introduction


Source: Abdulla, Parosh Aziz - Department of Information Technology, Uppsala Universitet


Collections: Computer Technologies and Information Sciences