Re: By The Dawn's Normal Light

From: Alfredo Novoa <anovoa_at_ncs.es>
Date: Sun, 24 Oct 2004 04:32:38 +0200
Message-ID: <oq4mn0dk75gcose5ageb2pk25tpgelfd3r_at_4ax.com>


On Sat, 23 Oct 2004 07:26:44 -0400, "Laconic2" <laconic2_at_comcast.net> wrote:

>> > > A table represents a set if and only if there is a candidate key.
>> > You are moving the concept of normal form from the logical level to the
>> > physical level.
>>
>> Why?
>>
>> Candidate keys are at the logical level.
>>
>In "zero normal form" (a whimsical name, in case you didn't notice) I am
>trying to link the physical level, represented by tables, to the logical
>level, represented by relations.

I thought you were talking about logical SQL tables :-?

It does not make sense to compare an internal physical table with a relation.

>If I think in relations, but I build in tables, I need some kind of link.

You build in logical tables. SQL tables are logical.

An SQL table represents a relation if and only if it does not allow nulls and it has at least a candidate key.

"Table" in SQL, is a name for a multiset that allows nulls (so it is not a multiset at all).

If a DBMS uses bidimensional arrays to represent tables internally then we can talk about physical tables. But of course they are not SQL tables. A DBMS may use any other internal representation for SQL tables.

Regards Received on Sun Oct 24 2004 - 04:32:38 CEST

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