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    How many variables are needed to express an existential positive query?

    Bova, S. and Chen, Hubie (2018) How many variables are needed to express an existential positive query? Theory of Computing Systems , ISSN 1432-4350. (In Press)

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    Abstract

    The number of variables used by a first-order query is a fundamental measure which has been studied in numerous contexts, and which is known to be highly relevant to the task of query evaluation. In this article, we study this measure in the context of existential positive queries. Building on previous work, we present a combinatorial quantity defined on existential positive queries; we show that this quantity not only characterizes the minimum number of variables needed to express a given existential positive query by another existential positive query, but also that it characterizes the minimum number of variables needed to express a given existential positive query, over all first-order queries. Put differently and loosely, we show that for any existential positive query, no variables can ever be saved by moving out of existential positive logic to first-order logic. One component of this theorem's proof is the construction of a winning strategy for a certain Ehrenfeucht-Fra\"{i}ss\'{e} type game.

    Metadata

    Item Type: Article
    Additional Information: The final publication is available at Springer via the link above.
    School: Birkbeck Schools and Departments > School of Business, Economics & Informatics > Computer Science and Information Systems
    Depositing User: Hubert Chen
    Date Deposited: 16 Nov 2018 09:28
    Last Modified: 05 Sep 2019 04:46
    URI: http://eprints.bbk.ac.uk/id/eprint/25143

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