Re: By The Dawn's Normal Light
From: Paul <paul_at_test.com>
Date: Fri, 22 Oct 2004 10:04:55 +0100
Message-ID: <4178cd36$0$47980$ed2e19e4_at_ptn-nntp-reader04.plus.net>
>
> This definition is a problem, because it includes two other terms that
> may themselves be subject to confusion: "compound" and "multivalued."
Date: Fri, 22 Oct 2004 10:04:55 +0100
Message-ID: <4178cd36$0$47980$ed2e19e4_at_ptn-nntp-reader04.plus.net>
Marshall Spight wrote:
>>A Relation is in first normal form if and only if none of the domains of its >>attributes permit compound or multivalued values.
>
> This definition is a problem, because it includes two other terms that
> may themselves be subject to confusion: "compound" and "multivalued."
To clarify it a bit more, maybe it should be:
"A Relation is in first normal form if and only if none of the domains
of its attributes permit compound or multivalued values *from the point
of view of the relational engine*."
Of course, a string could be viewed as a compound value by the type
engine, which is why you get type operators like "substring" etc. But
from the point of view of the relational engine, a string is atomic:
there is no way for the relational operators to break it down into
smaller pieces.
Paul. Received on Fri Oct 22 2004 - 11:04:55 CEST