On the power of tree-walking automata

On the Power of Tree-Walking Automata

Tree walking automata TWAs recently received new attention in the elds of formal languages and databases Towards a better understanding of their expressiveness we characterize them in terms of transitive closure logic formulas in normal form It is conjectured by Engelfriet and Hoogeboom that TWAs cannot de ne all regular tree languages or equivalently all of monadic second order logic We proof ...

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.

Pebble Alternating Tree-Walking Automata and Their Recognizing Power

Pebble tree-walking automata with alternation were first investigated by Milo, Suciu and Vianu (2003), who showed that tree languages recognized by these devices are exactly the regular tree languages. We strengthen this by proving the same result for pebble automata with “strong pebble handling” which means that pebbles can be lifted independently of the position of the reading head and withou...