Re: Proposal: 6NF

"David Cressey" <dcressey_at_verizon.net> wrote in message news:DqsVg.853$Ye.350_at_trndny04...
>
> "Brian Selzer" <brian_at_selzer-software.com> wrote in message
> news:hwoVg.7861$TV3.6237_at_newssvr21.news.prodigy.com...
>
>> I agree that decomposition into separate relations still has its place.
> I
>> just don't think that nulls should be dismissed arbitrarily.
>>
>> After further consideration (prompted by Bob's harangue), I think that
>> the
>> results of some of the operators enumerated above are not sensible. Ø
>> does
>> not belong to any numeric domain, and you can't add apples and oranges,
> but
>> on the other hand, there is only one empty set, so Ø = Ø should be TRUE.
>>
>
> I've been following your discussion on this subject, and I largely agree
> with the major points you've been making. (Unusual, since we've disagreed
> in the past).
>
> I also agree with the above, that nulls should not be dismissed
> arbitrarily.
> In another subthread, I'm trying to develop the theme one point at a time.
> Where I actaully get to depends on the responses I get.
>
> But here's where I anticipate getting to: as a theoretical tool, nulls
> are
> unnecessary. A system without nulls can be just as expressive as one with
> nulls. As a practical matter nulls are just about indispensable. A
> system
> built with no accomodation for nulls just isn't going to work as
> practically
> as one that allows for nulls.
>
> Where I'm very uncertain is whether admitting nulls inescapably leads to
> 3VL. I think not. But I'm not there yet.
>
> But on nulls and the empty set. The empty set is very clearly a value.
> Null is very clearly not a value. Using the empty set in place of a null
> is
> very clearly the road to confusion.
>
> There is one point I'm confused on: what is the domain of the empty set?
> does it even have a domain? To me, the empty set of character strings is
> not "the same thing" as the empty set of integers. But I may be thinking
> like a computer person and not like a mathematician.
>

The way I see it, the domain of the empty set is the set of all sets, which does not exist.

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>
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Received on Sun Oct 08 2006 - 15:56:01 CEST