Querying disjunctive databases through nonmonotonic logics

  • Piero A. Bonatti
  • Thomas Eiter
Contributed Papers Nonmonotonic Semantics I
Part of the Lecture Notes in Computer Science book series (LNCS, volume 893)

Abstract

In this paper we study the expressive power of major nonmonotonic formalisms — among them circumscription, default logic, and autoepistemic logic — used as query languages over disjunctive databases. For this aim, we define the semantics of query expressions formulated in different nonmonotonic logics. The expressive power of the languages that we consider has been explored in the context of relational databases. Here, we extend this study to disjunctive databases; as a result, we obtain a finer-grained characterization of the expressive capabilities of those languages and interesting fragments thereof.

In particular, we show that there exist queries that cannot be expressed by any preference-based semantics (including the minimal model semantics and the various forms of circumscription), but which can be expressed in default and autoepistemic logic. Secondly, we show that default logic, autoepistemic logic and some of their fragments express the same class of Boolean queries, which turns out to be a strict subclass of the 2p-recognizable Boolean queries. Then we prove that under the assumption that the database consists of clauses whose length is bound by some constant, default logic and autoepistemic logic express all of the 2p-recognizable Boolean queries, while preference-based logics do not.

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Copyright information

© Springer-Verlag 1995

Authors and Affiliations

  • Piero A. Bonatti
    • 1
  • Thomas Eiter
    • 2
  1. 1.Dipartimento di InformaticaUniversità di TorinoTorinoItaly
  2. 2.Christian Doppler Lab for Expert Systems, Institut für InformationssystemeTU WienWienAustria

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