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    The additivity problem for functional dependencies in incomplete relations

    Levene, Mark and Loizou, G. (1997) The additivity problem for functional dependencies in incomplete relations. Acta Informatica 34 (2), pp. 135-149. ISSN 0001-5903.

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    Incomplete relations are relations which contain null values, whose meaning is “value is at present unknown”. A functional dependency (FD) is weakly satisfied in an incomplete relation if there exists a possible world of this relation in which the FD is satisfied in the standard way. Additivity is the property of equivalence of weak satisfaction of a set of FDs, say F, in an incomplete relation with the individual weak satisfaction of each member of F in the said relation. It is well known that satisfaction of FDs is not additive. The problem that arises is: under what conditions is weak satisfaction of FDs additive. We solve this problem by introducing a syntactic subclass of FDs, called monodependent FDs, which informally means that for each attribute, say A, there is a unique FD that functionally determines A, and in addition only trivial cycles involving A arise between any two FDs one of which functionally determines A. We show that weak satisfaction of FDs is additive if and only if the set F of FDs is monodependent and that monodependence can be checked in time polynomial in the size of F.


    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 08:44
    Last Modified: 09 Aug 2023 12:51


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