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Functional queries in Datalog

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Abstract

A ‘functional’ query is a query whose answer is always defined and unique i.e. it is either true or false in all models. It has been shown that the expressive powers of the various types of stable models, when restricted to the class of DATALOG¬ functional queries, do not in practice go beyond those of well-founded semantics, except for the least undefined stable models which, instead, capture the whole boolean hierarchyBH.

In this paper we present a ‘functional’ language which, by means of a disciplined use of negation, achieves the desired level of expressiveness up toBH. Although the semantics of the new language is partial, all atoms in the source program are defined and possibly undefined atoms are introduced in a rewriting phase to increase the expressive power. We show that the language satisfies ‘desirable’ properties better than classical languages with (unstratified) negation and stable model semantics. We present an algorithm for the evaluation of functional queries and we show that exponential time resolution is required for hard problems only. Finally we present the architecture of a prototype of the language which has been developed.

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Author information

Authors and Affiliations

  1. ISI-CNR, via P.Bucci, 87036, Rende, Italy

    Stefano Basta

  2. DEIS-Università della Calabria, via P.Bucci, 87036, Rende, Italy

    Sergio Flesca & Sergio Greco

Authors
  1. Stefano Basta
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  2. Sergio Flesca
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  3. Sergio Greco
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Correspondence to Stefano Basta.

Additional information

Stefano Basta, Ph.D.: He received his Ph.D. in “Ingegneria dei Sistemi e Informatica” from University of Calabria, Italy in 2000. Since December 2000, he is Researcher for Institute of Systems Analysis and Information Technology of National Research Council (ISI-CNR). His research interests include logic programming, deductive databases, knowledge representation, information integration, data mining and data warehousing.

Sergio Flesca, Ph.D.: He received his Ph.D. in computer science engineering at the university of Calabria, Italy. Currently he is a researcher in the Engineering Faculty at the University of Calabria. He was a visiting researcher at the Computer Science Department of Vienna University of Technology. His research interests include deductive and active database, semistructured data, XML query languages and XML wrapper induction.

Sergio Greco, Ph.D.: He received his laurea degree in electrical engineering from University of Calabria, Italy. Currently, he is a full professor at the faculty of Enginering at the University of Calabria. Prior of this, he was researcher at CRAI, a research consortium in Informatics and assistant professor at the University of Calabria. He was a visiting researcher at the research center of Microelectronics and Computer Center (MCC) of Austin (Texas) and at the Computer Science Department of University of California at Los Angeles. His area of research includes database theory, deductive database, logic programming, and query languages.

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Basta, S., Flesca, S. & Greco, S. Functional queries in Datalog. New Gener Comput 20, 339–371 (2002). https://doi.org/10.1007/BF03037371

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