A Trichotomy in the Complexity of Counting Answers to Conjunctive Queries

Hubie Chen; Stefan Mengel

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arXiv · 1408.0890

A Trichotomy in the Complexity of Counting Answers to Conjunctive Queries

Hubie Chen·Stefan Mengel

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Abstract

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.

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BibTeX RIS

Hubie Chen, Stefan Mengel. 2014-08-05. A Trichotomy in the Complexity of Counting Answers to Conjunctive Queries. https://arxiv.org/abs/1408.0890

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