Re: two nasty schemata, union types and surrogate keys

From: paul c <toledobythesea_at_oohay.ac>
Date: Sun, 27 Sep 2009 13:57:01 GMT
Message-ID: <NaKvm.45452$Db2.31766_at_edtnps83>



Brian wrote:
...
> And it's wrong! Normalization has everything to do with the semantics
> of the data. If you look carefully at all of the examples of
> converting from one normal form to the next higher form, you'll see
> that the schema before conversion and the one after conversion are NOT
> equivalent in their capacity to express facts. Instead, the schema
> after conversion has at least the same capacity to express facts, but
> not exactly the same capacity. For example, a 2NF schema that is not
> in 3NF, ...

This could be extremely misleading to the casual reader. In one breath, it suggests a set-piece that recasts relations under the guise of normalization but ignoring constraints at the same time. In fact, when normalizing, one must nearly always introduce constraints in order to preserve "semantics". Most trade writers make the same mistake which may be why so many people think re-design involves only normalization. Received on Sun Sep 27 2009 - 08:57:01 CDT

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