[Informatics] Query on Practice exam solution

[Mark]

Yep. Repeated fields are 1NF.

2NF means that any non-key field in a table is dependent on ALL of the
fields that make up the key.

Of course this only applies if multiple existing fields are combined to
create a key for a table - which is a dumb move that no database developer
in their right mind does because there is no guarantee that a duplicate key
will never arise in the future.

For example, using FamilyName + GivenName + Street + Birthdate as a key may
eventually still yield a duplicate key that will break the database's
integrity.

Wise designers create a new single key field containing arbitrary and
guaranteed-unique data especially for the occasion - typically an account
number or product ID.
A single-field key guarantees that 2NF problems will never arise.

This is why I get so weary about 2NF exam questions: very basic common
sense in database design prevents 2NF problems from ever happening.
Database developers with 2NF problems have only themselves to blame.

Gary Larson's Far Side
<http://www.defordmusic.com/wp-content/uploads/what-site-changes-do.jpg>
demonstrates it best.

Regards,
Mark



On 28 October 2016 at 10:48, Joseph Papaleo <joseph.papaleo at avemaria.vic.
edu.au> wrote:

> Hi all,
>
>
>
> I am seeking some clarity please on normalisation.
>
>
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> A practice exam multiple choice question asks students to identify which
> table has achieved FIRST normal form.  The solutions provided refer to
> answer D being incorrect as there are repeated records.  Isn’t this 2nd
> normal form?
>
>
>
> Thanks
>
> Joseph
>
>
>
>
>
>
>
>
>
>
>
>
>
> Joseph Papaleo
>
> Member of Staff
>
>
> [image: Ave Maria College] <http://www.avemaria.vic.edu.au>
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-- 

Mark Kelly

mark at vceit.com
http://vceit.com
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