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Re: Pizza Example

From: Dawn M. Wolthuis <dwolt_at_tincat-group.com>
Date: Wed, 7 Apr 2004 08:13:47 -0500
Message-ID: <c50ur6$5ds$1@news.netins.net>


<snip> > You now have the equivalent of a Pick RECORD (a bit like your
> > row). We don't duplicate a simple attribute because it doesn't make
> > sense to do so
>
> In what sense does the relational model duplicate an attribute?
>
> > why list it repeatedly when it only exists once per object?
>
> There are multiple values which may be associated with X, but in what
sense
> is it "listed repeatedly"? Again, I don't see the "duplication."
>

I suspect that Anthony was thinking of the output of a SQL SELECT statement. He might not realize that the property of closure is not extended to queries in the relational model. That's my guess as to the gap on this one.

With a relational database, a query might result in

Jon Doe Pizza
Jon Doe Garlic Bread

rather than

Jon Doe Pizza

              Garlic Bread

When MV folks (PICK) look at SQL output, we shudder. Date's use of GROUP BY and UNGROUP as relational operators (IIRC) helps with this. But SQL does not take tables/views and output the same -- no closure there as we (MV/PICK folks) are accustomed to.

Cheers! --dawn Received on Wed Apr 07 2004 - 08:13:47 CDT

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