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>


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.

So this way you don't really need a definition of compound or multi-valued, you just need to know that to the relational engine the values are "black boxes" or "atoms" that can't be subdivided in any way.

Paul. Received on Fri Oct 22 2004 - 11:04:55 CEST

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