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    Inferring null join dependencies in relational databases

    Levene, Mark and Loizou, G. (1992) Inferring null join dependencies in relational databases. BIT Numerical Mathematics 32 (3), pp. 413-429. ISSN 0006-3835.

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    The inference problem for data dependencies in relational databases is the problem of deciding whether a set of data dependencies logically implies another data dependency. For join dependencies (JDs), the inference problem has been extensively studied by utilising the well-known chase procedure. We generalise JDs to null join dependencies (NJDs) that hold in relations which may contain null values. In our model for incomplete information we allow only a single unmarked null value denoted bynull. This allows us to solve the inference problem for NJDs by extending the chase procedure to the or-chase procedure. In order to define the or-chase procedure we generalise relations with nulls to or-relations which contain a limited form of disjunctive information. The main result of the paper shows that the inference problem for NJDs, including embedded NJDs (which are a special case of NJDs), is decidable; this is realised via the or-chase procedure.


    Item Type: Article
    School: Birkbeck Faculties and Schools > Faculty of Science > School of Computing and Mathematical Sciences
    Depositing User: Sarah Hall
    Date Deposited: 14 Jun 2021 16:56
    Last Modified: 09 Aug 2023 12:51


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