On Nondeterministic Unranked Tree Automata with Sibling Constraints

ABSTRACT. We continue the study of bottom-up unranked tree automata with equality and disequality constraints between direct subtrees. In particular, we show that the emptiness problem for the nondeterministic automata is decidable. In addition, we show that the universality problem, in contrast, is undecidable.

• Type: Conference
• Year: 2009
• Where: FSTTCS
• Authors: Christof Löding, Karianto Wong
• Keywords: Emptiness Problem, FSTTCS 2009, Nondeterministic Automata, Theoretical Computer Science, Unranked Tree Automata