Re: Perhaps an idiotic question
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Thu, 30 Nov 2006 23:41:50 GMT
Message-ID: <2%Jbh.27048$cz.408998_at_ursa-nb00s0.nbnet.nb.ca>
Date: Thu, 30 Nov 2006 23:41:50 GMT
Message-ID: <2%Jbh.27048$cz.408998_at_ursa-nb00s0.nbnet.nb.ca>
Gene Wirchenko wrote:
> Bob Badour <bbadour_at_pei.sympatico.ca> wrote:
>
>>Gene Wirchenko wrote: >> >>>paul c <toledobythesea_at_oohay.ac> 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)? >>> >>> I see recursion but no termination. >>> >>> What *is* the use of such a declaration? >> >>What would be the type of a view that combines a recursion or closure >>with the GROUP operation?> is the case, the type can not declared in the first place.
>
> I do not know since I see recursion but no termination. If that
Sure, it can. It just requires a forward reference.
> I can see the attribute being an FK into its own relation. The
> type then is more pointer to R than R. (That wording is not quite
> right, but I hope the concept comes through.)
Suppose you have a reference from R1 to R1. e.g. Employee relation has a Manager reference to Employee. You declare a recursive view that groups the manager references as a relation valued attribute.
Whether the recusion terminates depends on what you did with the CEO's manager reference and how you wrote the recursion. Received on Fri Dec 01 2006 - 00:41:50 CET