On the consistent rewriting of conjunctive queries under primary key constraints

  • Authors:
  • Jef Wijsen

  • Affiliations:
  • Université de Mons, Place du Parc 20, B-7000 Mons, Belgium

  • Venue:
  • Information Systems
  • Year:
  • 2009

Quantified Score

Hi-index 0.00

Visualization

Abstract

This article deals with the computation of consistent answers to queries on relational databases that violate primary key constraints. A repair of such inconsistent database is obtained by selecting a maximal number of tuples from each relation without ever selecting two distinct tuples that agree on the primary key. We are interested in the following problem: Given a Boolean conjunctive query q, compute a Boolean first-order (FO) query @j such that for every database db, @j evaluates to true on db if and only if q evaluates to true on every repair of db. Such @j is called a consistent FO rewriting of q. We use novel techniques to characterize classes of queries that have a consistent FO rewriting. In this way, we are able to extend previously known classes and discover new ones. Finally, we use an Ehrenfeucht-Fraisse game to show the non-existence of a consistent FO rewriting for @?x@?y(R(x@?,y)@?R(y@?,c)), where c is a constant and the first coordinate of R is the primary key.