Re: No exceptions?
Date: Fri, 30 Jun 2006 22:47:28 GMT
Message-ID: <4Shpg.4313$pu3.101351_at_ursa-nb00s0.nbnet.nb.ca>
paul c wrote:
> paul c wrote:
>
>> Jon Heggland wrote: >> >>> paul c wrote: >>> >>>> Let me re-phrase my original question: Is there a logical flaw in >>>> substituting TABLE_DUM for x in the expression "x join y" when x is not >>>> in the catalogue? >>>> >>> >>> I don't know what precisely you mean by "logical flaw", so I'll pass >>> judgement. If something should be substituted for x (a "default value", >>> so to speak), TABLE_DUM does seem the natural choice, though, as it >>> corresponds to false/zero in some sense. >>> ...
>
> I suppose my "logic", if I may call it that, went like this (at
> evaluation time):
>
> 1) according to syntax, x must be a relation
What about the relation 'x = true' ? Or rather 'x != false' ?
> 2) according to the catalogue, there are no attributes for a relation
> named x, so given that the syntax insists x is a relation, it must be
> the same relation as either TABLE_DEE or TABLE_DUM
Or it could be a boolean expression. If one treats 'x = 1' as a relation to handle restrict, then naturally x by itself is a boolean assertion. Is it not?
> 3) because x is not in the catalogue, it has no tuple in the database
But in the case of 'x = 1', x is not a relation and is not in the catalog. Is it?
> 4) since x has no attributes and no tuple, it must have the same value
> as TABLE_DUM
Or it could be an expression that evaluates to a whole set of values.
> That seems okey-dokey, but what if I make an innocuous change to step 3,
> eg.,
>
> 3) because x is not in the catalogue, it has no known value in the database
>
> Now, it seems I'm stuck, the choice between DEE and DUM is
> indeterminate. So I guess by logical flaw, I meant either a mistake in
> the reasoning OR a misleading assumption.
>
> p
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Received on Sat Jul 01 2006 - 00:47:28 CEST