Re: Proposal: 6NF
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Fri, 06 Oct 2006 13:29:53 GMT
Message-ID: <lTsVg.1242$cz.18087_at_ursa-nb00s0.nbnet.nb.ca>
>
> I
>
>
> but
>
>
>
> I've been following your discussion on this subject, and I largely agree
> with the major points you've been making. (Unusual, since we've disagreed
> in the past).
>
> I also agree with the above, that nulls should not be dismissed arbitrarily.
> In another subthread, I'm trying to develop the theme one point at a time.
> Where I actaully get to depends on the responses I get.
>
> But here's where I anticipate getting to: as a theoretical tool, nulls are
> unnecessary. A system without nulls can be just as expressive as one with
> nulls. As a practical matter nulls are just about indispensable. A system
> built with no accomodation for nulls just isn't going to work as practically
> as one that allows for nulls.
>
> Where I'm very uncertain is whether admitting nulls inescapably leads to
> 3VL. I think not. But I'm not there yet.
>
> But on nulls and the empty set. The empty set is very clearly a value.
> Null is very clearly not a value. Using the empty set in place of a null is
> very clearly the road to confusion.
>
> There is one point I'm confused on: what is the domain of the empty set?
> does it even have a domain? To me, the empty set of character strings is
> not "the same thing" as the empty set of integers. But I may be thinking
> like a computer person and not like a mathematician.
Date: Fri, 06 Oct 2006 13:29:53 GMT
Message-ID: <lTsVg.1242$cz.18087_at_ursa-nb00s0.nbnet.nb.ca>
David Cressey wrote:
> "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 empty set is the empty set. Its most specific type is a subtype of every set type, and has only one proper subtype: the universal subtype.
In general, a set can contain strings, integers, cars and trees or anything else. When you speak of a string set or an integer set, you are implicitly defining a proper subtype of set via specialization by constraint. Received on Fri Oct 06 2006 - 15:29:53 CEST