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Erschienen in:
2006 | OriginalPaper | Buchkapitel
Interpreting Tree-to-Tree Queries
verfasst von : Michael Benedikt, Christoph Koch
Erschienen in: Automata, Languages and Programming
Verlag: Springer Berlin Heidelberg
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We establish correspondences between top-down tree building query languages and predicate logics. We consider the expressive power of the query language
XQ
, a clean core of the practitioner’s language XQuery. We show that all queries in
XQ
with only atomic equality are equivalent to “first-order interpretations”, an analog to first-order logic (FO) in the setting of transformations of tree-structured data. When
XQ
is considered with deep equality, we find that queries can be translated into FO with counting (
FO
(
Cnt
)). We establish partial converses to this, characterizing the subset of the FO resp.
FO
(
Cnt
) interpretations that correspond to
XQ
. Finally, we study the expressive power of fragments of
XQ
and obtain partial characterizations in terms of existential FO and a fragment of FO that is two-variable if the tree node labeling alphabet is assumed fixed.