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ICDT
2001
ACM

Query Evaluation via Tree-Decompositions

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Query Evaluation via Tree-Decompositions
A number of efficient methods for evaluating first-order and monadic-second order queries on finite relational structures are based on tree-decompositions of structures or queries. We systematically study these methods. In the first part of the paper we consider arbitrary formulas on tree-like structures. We generalize a theorem of Courcelle [8] by showing that on structures of bounded tree-width a monadic second-order formula (with free first- and second-order variables) can be evaluated in time linear in the structure size plus the size of the output. In the second part we study tree-like formulas on arbitrary structures. We generalize the notions of acyclicity and bounded tree-width from conjunctive queries to arbitrary first-order formulas in a straightforward way and analyze the complexity of evaluating formulas of these fragments. Moreover, we show that the acyclic and bounded tree-width fragments have the same expressive power as the wellknown guarded fragment and the fi...
Jörg Flum, Markus Frick, Martin Grohe
Added 29 Jul 2010
Updated 29 Jul 2010
Type Conference
Year 2001
Where ICDT
Authors Jörg Flum, Markus Frick, Martin Grohe
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