ER and Normalization [Archive]

andrewst

09-23-02, 09:08

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.

DerekA

09-25-02, 10:39

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)