Re: Perhaps an idiotic question

From: paul c <>
Date: Thu, 30 Nov 2006 01:49:52 GMT
Message-ID: <4Nqbh.390700$5R2.215690_at_pd7urf3no>

Bob Badour wrote:
> paul c wrote:

>> But it perplexes me even though I admit I have no good reason for asking:
>> If I declare a relation (or more properly a relvar) R to have an 
>> attribute A where A's type is the type of R am I declaring a fallacy 
>> or something that is logically possible (ignoring whether it has any 
>> use)?
>> p

> You are re-using the same symbols for too many things. I think what you
> are saying is you have relvar R with type T. Type T has an attribute A
> with type T.
> First, to make the declaration, your language has to make some sort of
> forward reference to the type. Second, to have this exactly as stated
> yields a potentially infinite progression of the type. In practical
> terms, one would have to settle for a finite recursion because computers
> are finite machines. ie. If one serially ungroups the A attribute, at
> some finite step, ungrouping would yield an empty relation with
> cardinality zero.
> The question is: Would such a thing have any practical use? I would
> answer a hesitant and cautious "Yes--in very rare circumstances."

Thanks for that. I agree about the forward reference but it seems non-controversial, eg., not uncommon, to me and as well about the infiniteness (which might be the aspect that intrigued me). As for the infiniteness, I don't want to distract into what's practical and what's not except to say that we sometimes ignore infinite issues in practice, given enough memory we are sometimes prepared to let things 'fall apart' at some point, eg., crash/fail as long as we never get a wrong answer for the progressions we can handle.

I had a little trouble expressing my question using more than two variables, perhaps that's one reason why it might be seen as idiotic.

p Received on Thu Nov 30 2006 - 02:49:52 CET

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