Handbook of formal languages, vol. 3
Languages, automata, and logic
Handbook of formal languages, vol. 3
Acta Cybernetica
Data on the Web: from relations to semistructured data and XML
Data on the Web: from relations to semistructured data and XML
Typechecking for XML transformers
PODS '00 Proceedings of the nineteenth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Expressive and efficient pattern languages for tree-structured data (extended abstract)
PODS '00 Proceedings of the nineteenth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Domains of partial attributed tree transducers
Information Processing Letters
A comparison of tree transductions defined by monadic second order logic and by attribute grammars
Journal of Computer and System Sciences
A formal model for an expressive fragment of XSLT
Information Systems - Databases: Creation, management and utilization
Jewels are Forever, Contributions on Theoretical Computer Science in Honor of Arto Salomaa
The Expressive Power of Transitive Closue and 2-way Multihead Automata
CSL '91 Proceedings of the 5th Workshop on Computer Science Logic
Journal of Computer and System Sciences
Visibly pushdown automata for streaming XML
Proceedings of the 16th international conference on World Wide Web
XPath, transitive closure logic, and nested tree walking automata
Proceedings of the twenty-seventh ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Deciding determinism of caterpillar expressions
Theoretical Computer Science
Transitive closure logic, nested tree walking automata, and XPath
Journal of the ACM (JACM)
Deterministic caterpillar expressions
CIAA'07 Proceedings of the 12th international conference on Implementation and application of automata
Nested pebbles and transitive closure
STACS'06 Proceedings of the 23rd Annual conference on Theoretical Aspects of Computer Science
Regular languages with variables on graphs
Information and Computation
Foundations of XML based on logic and automata: a snapshot
FoIKS'12 Proceedings of the 7th international conference on Foundations of Information and Knowledge Systems
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Tree-walking automata (TWAs) recently received new attention in the fields of formal languages and databases. To achieve 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 define all regular tree languages, or equivalently, all of monadic second-order logic. We prove this conjecture for a restricted, but powerful, class of TWAs. In particular, we show that 1-bounded TWAs, that is TWAs that are only allowed to traverse every edge of the input tree at most once in every direction, cannot define all regular languages. We then extend this result to a class of TWAs that can simulate first-order logic (FO) and is capable of expressing properties not definable in FO extended with regular path expressions; the latter logic being a valid abstraction of current query languages for XML and semistructured data.