Tree-walking automata cannot be determinized

Tree-Walking Automata Cannot Be Determinized

Tree-walking automata are a natural sequential model for recognizing languages of finite trees. Such automata walk around the tree and may decide in the end to accept it. It is shown that deterministic tree-walking automata are weaker than nondeterministic tree-walking automata.

Weighted Tree-Walking Automata

We define weighted tree-walking automata. We show that the class of tree series recognizable by weighted tree-walking automata over a commutative semiring K is a subclass of the class of regular tree series over K. If K is not a ring, then the inclusion is strict.

Tree-Walking Pebble Automata

Tree-Walking Automata

A survey of tree-walking automata. The main focus is on how the expressive power is changed by adding features such as pebbles or nondeterminism.

Complementing deterministic tree-walking automata

We consider various kinds of deterministic tree-walking automata, with and without pebbles, over ranked and unranked trees. For each such kind of automata we show that there is an equivalent one which never loops. The main consequence of this result is the closure under complementation of the various types of automata we consider with a focus on the number of pebbles used in order to complement...