Monotone AC-Tree Automata

Hitoshi Ohsaki (1) , Jean-Marc Talbot (2, 3) , Sophie Tison (2, 3) , Yves Roos (2, 3)

1 Institute of Scientific and Industrial Research
2 MOSTRARE - Modeling Tree Structures, Machine Learning, and Information Extraction
3 LIFL - Laboratoire d'Informatique Fondamentale de Lille

This paper considers several questions about monotone AC-tree automata, a class of equational tree automata whose transition rules correspond to rules in Kuroda normal form of context-sensitive grammars. Whereas it has been proved that this class has a decision procedure to determine if, given a monotone AC-tree automaton, it accepts no terms, other important decidability or complexity results have not been well-investigated yet. In the paper, it is proved that the membership problem for monotone AC-tree automata is PSPACE-complete. The expressiveness of monotone AC-tree automata is also studied: precisely, it is proved that the family of AC-regular tree languages is strictly subsumed in that of AC-monotone tree languages. The proof technique used in obtaining the above result yields the answers to two different questions, specifically that the family of monotone AC-tree languages is not closed under complementation, and that the inclusion problem for monotone AC-tree automata is undecidable.

Domaines: Langage de programmation [cs.PL]

Hitoshi Ohsaki, Jean-Marc Talbot, Sophie Tison, Yves Roos. Monotone AC-Tree Automata. 12th International Conference on Logic for Programming Artificial Intelligence and Reasoning, 2005, Montego Bay, Jamaica. pp.337-351. ⟨inria-00536693⟩