Re: 2NF There are two Definitions which is right

From: Jonathan Leffler <jleffler_at_earthlink.net>
Date: Fri, 22 Jul 2005 05:59:26 GMT
Message-ID: <2X%De.6457$dU3.5034@newsread2.news.pas.earthlink.net>

Jon Heggland wrote:
> In article <3k7t18Ft6e3bU1_at_individual.net>, jens_at_haase.to says...
>

>>I found two definitions for 2NF:
>>
>>1: A relation R(A,F) is in 2NF, when every attribute not belonging to 
>>the primary key of R is fully functionally dependent on the primary key of R
>>
>>2: A relation schema R is in 2NF if every nonprime attribute A in R is 
>>fully functionally dependent on the primary key of R

>
> [8<]
>

>>Which definition is right?

>
> The second. Normalisation theory doesn't deal with the arbitrary primary
> key distinction. The first definition probably makes the assumption that
> there is only one key.

I'm probably just being obtuse, but ... both definitions talk about 'the primary key of R'. Given that prime attributes are components of some candidate key (and therefore non-prime attributes are not a component of any candidate key), the second is marginally more correct, but would be more convincingly so if it finished 'dependent on each candidate key of R'.

I can't help but feel that the distinction between the two statements is trivial - they are near enough equivalent.

-- 
Jonathan Leffler                   #include <disclaimer.h>
Email: jleffler_at_earthlink.net, jleffler_at_us.ibm.com
Guardian of DBD::Informix v2005.01 -- http://dbi.perl.org/

Received on Fri Jul 22 2005 - 00:59:26 CDT