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    Non trivial functional dependencies


    Hi

    Im not sure if this is the correct place to post this but it is to do with database management slightly.

    I am basically having a problem with a possible exam question for my degree exam module database systems.

    I have searched google, wikipedia, my lecture notes and some paper i found from toronto and am still having trouble understanding a non trivial functional dependency!

    I know that a functional dependency is when:

    A -> B (A determines B)
    B -/> A (B is determined by A) -/> meant to be does not determine!

    Ive read my notes and it says that a functional dependency is trivial if satisfied by all tuples. However I dont really understand this.

    My exam question is as follows:

    Give a full explanation of the terms functional dependency (FD) and non-trivial FD.

    List all the non-trivial functional dependencies (FDs) satisified in the following table


    Code:
       A       B       C
       a1     b1      c1
       a1     b1      c2
       a2     b1      c1
       a2     b1      c3
    Please if someone knows could they tell me as Ive been trawling the net for an hour and a half on this question and still havent worked it out. Please if possible do not link me to more pages Im sure its a lot simpler than im making it out to be!


    Thanks in advance

    Billabang
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    Sadly didnt get a lot of response in the forum. Must admit that doesnt happen often though

    Ive found out that non trivial functional dependencies are anthing that is NOT:

    A -> A (where an attribute determines itself)
    A -> B where B is contained in or is a subset of A

    As these are all trivial and therefore NOT useful.

    The non trivial FDs from that table are as follows:

    a1 -> b1
    a2 -> b1
    c1 -> b1
    c2 -> b2


    Hope this helps anyone that gets the same problem

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