Re: choice of character for relational division

On Mar 31, 9:08 am, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
> Marshall wrote:
> > Let us consider the choice of characters to use for
> > relational operators. It might be desirable to use
> > different characters for the relational operators from
> > the scalar ones, so we avoid using * for join, even
> > though it is in some sense a product operator.
>
> > Set subtraction already has a standard character
> > in common usage: \
>
> > But we also need a character for relational division.
> > The / character is often used, but that's the same
> > as numerical division. Bummer.
>
> > So, if you had to choose an ascii character for
> > relational division, which one would you use
> > and why?
>
> Does a unique relational "division" exist?

Well, I think so. It's in TTM, no? Suppliers who supply all parts? That sort of thing?

> If "product" has a completely
> different name "join", why should a "divide" use the same name?

A fair question. The inverse of union is called "set subtraction" rather than just "subtraction." Maybe call it "inverse join?" "Unjoin?" "Relational division?"

> If we have an equality operation for relations, does a "divide"
> operation give us all that much?

I believe it does.

Marshall Received on Sat Mar 31 2007 - 23:17:43 CEST