# Re: No exceptions?

From: paul c <toledobythesea_at_oohay.ac>
Date: Sat, 01 Jul 2006 16:04:12 GMT
Message-ID: <02xpg.110590\$iF6.54066_at_pd7tw2no>

> 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' ?
> ...

Suspect I'm missing your point but I'll take a stab and guess that you are pointing out in an oblique way that I haven't specified whether x join y is a question or an answer?

>

>> 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?
> ...

Sorry, still feel I'm missing the point, not sure where 'x = 1' comes from.

>

>> 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.
> ...

Another guess, are you basically saying that as far as you're concerned, x could stand for anything and everything? If you are, then I guess there is a deep flaw in my assumption that I could stipulate via syntax that x is required to be a relation.

p Received on Sat Jul 01 2006 - 18:04:12 CEST

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