A remark on the complexity of consistent conjunctive query answering under primary key violations

نویسنده

  • Jef Wijsen
چکیده

A natural way for capturing uncertainty in the relational data model is by allowing relations that violate their primary key. A repair of such relation is obtained by selecting a maximal number of tuples without ever selecting two tuples that agree on their primary key. Given a Boolean query q, CERTAINTY(q) is the problem that takes as input a relational database and asks whether q evaluates to true on every repair of that database. In recent years, CERTAINTY(q) has been studied primarily for conjunctive queries. Conditions have been determined under which CERTAINTY(q) is coNP-complete, first-order expressible, or not first-order expressible. A remaining open question was whether there exist conjunctive queries q without self-join such that CERTAINTY(q) is in PTIME but not first-order expressible. We answer this question affirmatively.

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عنوان ژورنال:
  • Inf. Process. Lett.

دوره 110  شماره 

صفحات  -

تاریخ انتشار 2010