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  1. #1
    Join Date
    Feb 2012
    Posts
    1

    Help with Functional Dependencies

    If AB is the primary key.
    If the FD relation is say AB -> CD, A -> EF which normal form is it?

  2. #2
    Join Date
    Feb 2012
    Posts
    76
    You've got non-prime attributes (E and F) dependent on a proper subset (A ⊂ AB) of a candidate key (AB is the primary key). Do you understand why? If not, talk to me and I'll go into more depth.

    Knowing the fact above, you should be able to identify which normal form it isn't.

  3. #3
    Join Date
    Mar 2012
    Posts
    3

    I'm lost in FD too :(

    Hi! could you kindly tell me where can I study about FD simply and clearly. Kindly give me links of the sites. I'm completely lost and can't understand about FD. May be my mathematical skill isn't very good

  4. #4
    Join Date
    Feb 2012
    Posts
    76
    Try Functions versus Relations, and let me know if you have any questions. A functional dependency is just asking whether one value is a function of another. If you know fact A, can you determine fact B? If so, B has a functional dependency on A.

    For example, given a person's social security or national identity number, could you determine the person's birthday? In society, it may be difficult but since it's generally understood that those numbers uniquely identify a physical person, and that a person has a particular birthday, we can say that birthday has a functional dependency on social security number.

    Turning the relationship around, a given date doesn't determine a specific social security number, lots of people with different numbers are born on the same date. Social security number doesn't have a functional dependency on birthday.

  5. #5
    Join Date
    Mar 2012
    Posts
    3

    Thanks

    Thanks for the help.
    Now, I understand the basic idea and also will check the website you gave.
    Kindly let me PM you if I want to ask something more if I'm not clear about the concept.

    Thanks

  6. #6
    Join Date
    Feb 2012
    Posts
    76
    I don't mind more questions, but I prefer we keep it in the boards so that everyone can benefit. There are also other helpful and experienced posters here who can add valuable insight.

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