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    Null inclusion dependencies in relational databases

    Levene, Mark and Loizou, G. (1997) Null inclusion dependencies in relational databases. Information and Computation 136 (2), pp. 67-108. ISSN 0890-5401.

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    Functional dependencies (FDs) and inclusion dependencies (INDs) are the most fundamental integrity constraints that arise in practice in relational databases. We introduce null inclusion dependencies (NINDs) to cater for the situation when a database is incomplete and contains null values. We show that the implication problem for NINDs is the same as that for INDs. We then present a sound and complete axiom system for null functional dependencies (NFDs) and NINDs, and prove that the implication problem for NFDs and NINDs is decidable and EXPTIME-complete. By contrast, when no nulls are allowed, this implication problem is undecidable. This undecidability result has motivated several researchers to restrict their attention to FDs and noncircular INDs in which case the implication problem was shown to be EXPTIME- complete. Our results imply that when considering nulls in relational database design we need not assume that NINDs are noncircular.


    Item Type: Article
    School: Birkbeck Faculties and Schools > Faculty of Science > School of Computing and Mathematical Sciences
    Depositing User: Sarah Hall
    Date Deposited: 08 Jun 2021 08:58
    Last Modified: 09 Aug 2023 12:51


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