eng
Schloss Dagstuhl – Leibniz-Zentrum für Informatik
Leibniz International Proceedings in Informatics
1868-8969
2015-03-19
110
126
10.4230/LIPIcs.ICDT.2015.110
article
A Trichotomy in the Complexity of Counting Answers to Conjunctive Queries
Chen, Hubie
Mengel, Stefan
Conjunctive queries are basic and heavily studied database queries; in relational algebra, they are the select-project-join queries. In this article, we study the fundamental problem of counting, given a conjunctive query and a relational database, the number of answers to the query on the database. In particular, we study the complexity of this problem relative to sets of conjunctive queries. We present a trichotomy theorem, which shows essentially that this problem on a set of conjunctive queries is either tractable, equivalent to the parameterized CLIQUE problem, or as hard as the parameterized counting CLIQUE problem; the criteria describing which of these situations occurs is simply stated, in terms of graph-theoretic conditions.
https://drops.dagstuhl.de/storage/00lipics/lipics-vol031-icdt2015/LIPIcs.ICDT.2015.110/LIPIcs.ICDT.2015.110.pdf
database theory
query answering
conjunctive queries
counting complexity