# Re: Guessing?

From: paul c <toledobysea_at_ac.ooyah>
Date: Mon, 07 Jul 2008 23:52:27 GMT
Message-ID: <%_xck.84951\$gc5.52424_at_pd7urf2no>

Brian Selzer wrote:
...
> Consider the following statements:
>
> 1. Susan is an electrical engineer.
> 2. Susan is a mechanical engineer.
> 3. Susan is an electrical engineer or Susan is a mechanical engineer.
>
> Now, suppose you have a base relation P whose members map to individuals
> that exemplify the property of being an electrical engineer, a base relation
> Q whose members map to individuals that exemplify the property of being a
> mechanical engineer, and a virtual relation (a view) R (P UNION Q) whose
> members map to individuals that exemplify either the property of being an
> electrical engineer or the property of being a mechanical engineer or both.
> The presence of a tuple in the virtual relation with a value that maps to
> Susan tells us only that Susan exists and that she is either an electrical
> engineer or a mechanical engineer or both. It does not tell us which.

I think that what R = P <OR> Q "means" is that at any time, R always reflects what facts have been inserted to P and Q and says nothing about what has been inserted to R. If this is what David McGoveran means by POOD, I agree with him. People who know much more about computer languages than I have said this is non-deterministic behaviour, which is a nuance that has always escaped me. If they are right in the narrow scope of automation languages, I'm still not bothered.

Also, I'm happy to distribute over any view expression, difference, conjunction, etc., in any way that boolean logic allows. When it comes to projections, we get to the perhaps obscure area that I'm most interest in because I imagine something very fundamental must change, not just the notion of 'insert', but Codd's 1NF as well as the projection operator / aka existential quantification, itself. Received on Tue Jul 08 2008 - 01:52:27 CEST

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