Re: How to normalize this?
Date: Tue, 7 May 2013 16:07:49 +0200
Message-ID: <51890ab5$0$26892$e4fe514c_at_dreader37.news.xs4all.nl>
On 2013-05-07 13:22:55 +0000, nvitacolonna_at_gmail.com said:
>>
>> Normalization theory based on functional dependencies says nothing
>> about the inter-relational constraints of the decomposition
>
> “It says nothing about the inter-relational constraints of a database
> schema” would be more precise. Here is another example:
>
> R(A,B,C), {B -> A}
> S(D,E), {D -> E}
>
> R is not in 2NF, the only key being BC. Normalization theory would then
> suggest that it must be decomposed. Now, suppose that, in addition to
> the above, you impose R[B,C]⊆S[D,E] (a referential integrity constraint
> from (B,C) to (D,E). Would you still decompose R? Or would you do
> something else?
R is then in BCNF, since B has become a key. So no splitting needed.
- Jan Hidders