Re: Perhaps an idiotic question

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." Received on Thu Nov 30 2006 - 02:18:02 CET