Re: How to normalize this?

Op maandag 6 mei 2013 00:52:44 UTC+2 schreef Jan Hidders het volgende:
> On 2013-05-05 19:32:35 +0000, Erwin said:
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> > That one does have the inter-component rule that R1 JOIN R2 === R1 JOIN
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> > R3 (as I pointed out), no ?
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> Only if you want to be information-equivalent but conventional
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> normalization does not require that. It only aims at obtaining a
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> lossless decomposition.

Well there's the whole contradiction isn't it.

How can deliberate admission of "information differences" coexist with "aims of being lossless" ?

If "information differences" are deliberately allowed, this can mean either or both of two things : something may be added, something may be lost.

I contend that the "lossless" in conventional normalization can be upheld only for such a perverse and narrow meaning of the term that the claim (of having "lossless" decompositions) becomes essentially meaningless/futile/irrelevant/...

Lossless then seems to mean purely (exaggerating a little bit) that "all the original attributes are still in the design, somewhere, somehow". Relation schemas as mere sets of attributes, and normalization as manipulation/set-algebraic computation on sets of sets of attributes, and the only restriction being that the union of the final sets of attributes must be equal to the original set of attributes (/ union of sets of attributes). Received on Mon May 06 2013 - 14:26:10 CEST