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Re: No exceptions?

From: Bob Badour <>
Date: Fri, 30 Jun 2006 22:47:28 GMT
Message-ID: <4Shpg.4313$>

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

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
Received on Fri Jun 30 2006 - 17:47:28 CDT

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