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  1. #1
    Join Date
    Nov 2003
    Posts
    3

    how do u determine Functional Dependicies?

    Hi all,

    I'm new at this... but i have to design a database, but i wanted to avoid the pitalls of redundacy.. most examples i have worked with while learning this stuff gave me the fucntional dependencies.. if given a database with tables and relationships, how do i determine this?

    any examples or references would be appreciated

    thanks
    Janet

  2. #2
    Join Date
    Sep 2002
    Location
    UK
    Posts
    5,171

    Re: how do u determine Functional Dependicies?

    The only way to determine functional dependencies is to understand the requirements. This is part of the analysis phase - asking users questions about the relationships between different data items. Of course, some can be deduced using common sense and knowledge of the real world. But there is no "automatic" way to determine FD by inspecting attribute names alone, or even by looking at the data. Looking at the data can imply or disprove FDs, but it cannot prove them. For example, if you only have this:

    EmpName Dept DateOfBirth
    Smith Accounts 01/12/1970
    Jones Accounts 01/12/1970
    Brown HR 01/12/1970

    You might (if you were silly) think DateOfBirth is functionally dependent on Dept. Of course it isn't, but only knowledge of the real world tells us that.

    On the other hand, this data proves that there is NOT a functional dependency of EmpName on Dept, because you can see that a given Dept value corresponds to 2 different EmpName values.

  3. #3
    Join Date
    Oct 2003
    Posts
    107

    Re: how do u determine Functional Dependicies?

    Dennis Santoro wrote an excellent primer for data normalization that might be worth a quick read.

    http://www.rdaworldwide.com/pdox/datanorm.pdf

    This was aimed at Paradox Programmers but it is really platform independant in terms of concepts and structuring.

    Mac


    Originally posted by Xseptional
    Hi all,

    I'm new at this... but i have to design a database, but i wanted to avoid the pitalls of redundacy.. most examples i have worked with while learning this stuff gave me the fucntional dependencies.. if given a database with tables and relationships, how do i determine this?

    any examples or references would be appreciated

    thanks
    Janet

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