Theoretical Computer Science
Handbook of formal languages, vol. 3
Journal of the ACM (JACM)
Domains of partial attributed tree transducers
Information Processing Letters
Syntax-Directed Semantics: Formal Models Based on Tree Transducers
Syntax-Directed Semantics: Formal Models Based on Tree Transducers
Jewels are Forever, Contributions on Theoretical Computer Science in Honor of Arto Salomaa
Typechecking for XML transformers
Journal of Computer and System Sciences - Special issue on PODS 2000
Tree-walking automata do not recognize all regular languages
Proceedings of the thirty-seventh annual ACM symposium on Theory of computing
Tree-walking automata cannot be determinized
Theoretical Computer Science - Automata, languages and programming: Logic and semantics (ICALP-B 2004)
Complementing deterministic tree-walking automata
Information Processing Letters
Expressive power of pebble automata
ICALP'06 Proceedings of the 33rd international conference on Automata, Languages and Programming - Volume Part I
Weighted tree-walking automata
Acta Cybernetica
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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 without moving the reading head. Then we make a comparison among some restricted versions of these automata. We will show that the deterministic and non-looping pebble alternating tree-walking automata are strictly less powerful than their nondeterministic counterparts, i.e., they do not recognize all the regular tree languages. Moreover, there is a proper hierarchy of recognizing capacity of deterministic and non-looping n-pebble alternating tree-walking automata with respect to the number of pebbles, i.e., for each n ≥ 0, deterministic and non-looping (n + 1)-pebble alternating tree-walking automata are more powerful than their n-pebble counterparts.