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  1. #1
    Join Date
    Apr 2007

    Non loss decomposition

    I'm just revising for a database exam and can't remember how to work out if a decomposition is non loss:

    Relation T defined over attributes A,B,C,D,E
    Functional Dependancies: 
    Determine if decomposition of T into AB, BCD, ADE will be non-loss.
    Apparently this decomposition IS non loss.. but I can't tell how..
    (What to look for.. what to match...)

    According to the notes I made, the transitive dependencies, B -> A and D -> A are handy too

    Thanks for any help.

  2. #2
    Join Date
    May 2008
    Hi, I am revising for the same exam as well. You are probably from Imperial College.. ;p


    The common column of AB and BCD is B which is a determinant in AB as stated by the transitive dependency B->. So the decomposition between AB and BCD is non loss.

    The same goes for BCD, ADE where D is a determinant in ADE as stated by A-> E.

    Last, AD and ADE, D is a determinant in ADE since you've got A->D.

    So since the common columns are determinants in one of the two decomposed parts in each case, the decomposition will be non-loss.

    Hope this helps!

    P.S: There is a slight chance I got all of these wrong!

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