Re: Question about Date & Darwen <OR> operator

Mikito Harakiri wrote:

>
>
> Let A be a relation with attributes x and y. Let B has attributes y and
> z. Then,
>
> A <OR> (A <AND> B) != A
>
> , since the header of A <AND> B has attributes x,y,z. There is no way
> the subsequent <OR> operation to reduce it to x,y.
> ...

wouldn't that be a necessary consequence of having n-ary tuples?

(i should have mentioned that they do say that the purpose of the A-algebra is not to be implemented but rather to define the operators in the various descriptions in an exact way. however, i still find this topic interesting because i wonder about an "A" implementation in spite of D & D's stated intent. that's also why i wonder if there couldn't be some consistent and logical way of deciding to produce two or more relations as a result. even though <OR> could be avoided entirely, it is still a clearer way to read some expressions and it has seemed to me that when <OR> is involved it might make sense to keep its two relations separate.)

p Received on Sat Sep 03 2005 - 06:41:02 CEST