Re: No exceptions?
From: paul c <toledobythesea_at_oohay.ac>
Date: Sat, 01 Jul 2006 16:04:12 GMT
Message-ID: <02xpg.110590$iF6.54066_at_pd7tw2no>
>
> What about the relation 'x = true' ? Or rather 'x != false' ?
> ...
>
> Or it could be a boolean expression. If one treats 'x = 1' as a relation
> to handle restrict, then naturally x by itself is a boolean assertion.
> Is it not?
>
>
>
> But in the case of 'x = 1', x is not a relation and is not in the
> catalog. Is it?
> ...
>
> Or it could be an expression that evaluates to a whole set of values.
> ...
Date: Sat, 01 Jul 2006 16:04:12 GMT
Message-ID: <02xpg.110590$iF6.54066_at_pd7tw2no>
Bob Badour wrote:
> 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