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  1. #1
    Join Date
    Sep 2002
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    18

    ER and Normalization

    If I draw a correct ER model and have powerdesigner generate the sql script for me. Do I have to normalize the database or is it already normalized?

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

    Re: ER and Normalization

    Originally posted by oozypal
    If I draw a correct ER model and have powerdesigner generate the sql script for me. Do I have to normalize the database or is it already normalized?
    The generated database will be as normalised as the ER model you generated it from. If your ER model is correct and normalised, then your database will be too.

  3. #3
    Join Date
    Sep 2002
    Location
    Sydney, Australia
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    255
    Normalisation is an exercise you perform during the modelling stage. ER modelling tools (ERWin, PowerDesignor) assist (or hinder !) the modelling exercise (eg. by automatically generating cols in the child table, generating DDL, etc) but not in normalisation, I do not know of any tool that normalises for you. ERWin warns you of some apparent normalisation errors but these are your simple mistakes, not the moere serious normalisation errors.

    You need to read up on Normalisation. ER Modelling is both a science and an art. A fundamental requirement of relational databases is that they are Normalised. The result of normalisation (goal) is that changes to the db structure are isolated to the smallest area, ie. if you add a column, it affects only one table.

    Technically, for an ER model to be 'correct', it has to be normalised.

    Note there are distinctions between the following three:
    - Normalised (means correctly normalised, to at least Third Normal Form, and sometimes to fourth)
    - Denormalised (reversing the normalisation process for a variety of reasons, all bad)
    - Unnormalised (incorrectly or incompletely normalised)
    Last edited by DerekA; 09-25-02 at 10:59.
    Derek Asirvadem
    Senior Sybase DBA/Information Architect derekATsoftwaregemsDOTcomDOTau
    Anything worth doing is worth doing Right The First Time
    Spend your money on standards-compliant development or spend 10 times more fixing it

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