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Re: No exceptions?

From: paul c <toledobythesea_at_oohay.ac>
Date: Fri, 30 Jun 2006 22:31:23 GMT
Message-ID: <%Chpg.111333$Mn5.20411@pd7tw3no>


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
  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
  3. because x is not in the catalogue, it has no tuple in the database
  4. since x has no attributes and no tuple, it must have the same value as TABLE_DUM

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 - 17:31:23 CDT

Original text of this message

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