TU Berlin

Fachgebiet Algorithmische AlgebraDr. Stefan Mengel

Page Content

to Navigation

There is no English translation for this web page.

Ehemalige Mitarbeiter

Dr. Stefan Mengel


CRIL-CNRS/Université d'Artois
Faculté des Sciences Jean Perrin
rue Jean Souvraz, S.P. 18
F-62307 LENS Cedex
Persönliche Homepage

Publikationen in der Arbeitsgruppe

Structural Tractability of Counting of Solutions to Conjunctive Queries
Citation key DM-Structural-Tractability-Of-Counting-Of-Solutions-To-Conjunctive-Queries
Author Arnaud Durand and Stefan Mengel
Title of Book Proceeding of the 16th International Conference on Database Theory (ICDT 2013)
Year 2013
Abstract In this paper we explore the problem of counting solutions to conjunctive queries. We consider a parameter called the quantified star size of a formula ϕ which measures how the free variables are spread in ϕ. We show that for conjunctive queries that admit nice decomposition properties (such as being of bounded treewidth or generalized hypertree width) bounded quantified star size exactly characterizes the classes of queries for which counting the number of solutions is tractable. This also allows us to fully characterize the conjunctive queries for which counting the solutions is tractable in the case of bounded arity. To illustrate the applicability of our results, we also show that computing the quantified star size of a formula is possible in time $nO(k)$ for queries of generalized hypertree width $k$. Furthermore, quantified star size is even fixed parameter tractable parameterized by some other width measures, while it is W[1]-hard for generalized hypertree width and thus unlikely to be fixed parameter tractable. We finally show how to compute an approximation of quantified star size in polynomial time where the approximation ratio depends on the width of the input.
Link to publication Link to original publication Download Bibtex entry


Quick Access

Schnellnavigation zur Seite über Nummerneingabe