Re: teaching relational basics to people, questions

From: Sampo Syreeni <>
Date: Wed, 18 Nov 2009 08:53:00 -0800 (PST)
Message-ID: <>

On Nov 18, 1:08 am, wrote:

> Go read a definition carefully. Eg wiki dknf.
> It's in DK/NF iff all constraints follow from the domain and key ones.
> So it's not in DK/NF iff some constraint doesn't follow from the
> domain and key ones,
> In other words, if there other constraints is just isn't *in* DK/NF.

But that's just my point: we *assumed* DK/NF, so there cannot be any other constraints. 6NF should logically be subsumed, if not else then vacuously.

> (It's not a very useful concept.)

Personally I find it very useful, at least as a mental aid, because it forces one to concentrate on the possibility of constraining your schema just a little bit further. No matter the means.

Received on Wed Nov 18 2009 - 17:53:00 CET

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