Re: Perhaps an idiotic question

Bob Badour <bbadour_at_pei.sympatico.ca> wrote:

>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?
>>
>> I do not know since I see recursion but no termination. If that
>> is the case, the type can not declared in the first place.
>
>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.

     I do not see it. Could you please post some p-code?

Sincerely,

Gene Wirchenko

Computerese Irregular Verb Conjugation:

     I have preferences.
     You have biases.
     He/She has prejudices.