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2003
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Query containment and rewriting using views for regular path queries under constraints

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Query containment and rewriting using views for regular path queries under constraints
In this paper we consider general path constraints for semistructured databases. Our general constraints do not suffer from the limitations of the path constraints previously studied in the literature. We investigate the containment of regular path queries under general path constraints. We show that when the path constraints and queries are expressed by words, as opposed to languages, the containment problem becomes equivalent to the word rewrite problem for a corresponding semi-Thue system. Consequently, if the corresponding semi-Thue system has an undecidable word problem, the word query containment problem will be undecidable too. Also, we show that there are word constraints, where the corresponding semi-Thue system has a decidable word rewrite problem, but the general query containment under these word constraints is undecidable. In order to overcome this, we exhibit a large, practical class of word constraints with a decidable general query containment problem. Based on the que...
Gösta Grahne, Alex Thomo
Added 08 Dec 2009
Updated 08 Dec 2009
Type Conference
Year 2003
Where PODS
Authors Gösta Grahne, Alex Thomo
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