Re: Notions of Type

From: Marshall <marshall.spight_at_gmail.com>
Date: 17 Aug 2006 22:51:21 -0700
Message-ID: <1155880281.275059.136720@p79g2000cwp.googlegroups.com>

David Cressey wrote:
>
> I'm surprised the PROJECT is such a problem. Maybe I should stay out of the
> discussion, because this is a little over my head. But here goes, anyway:
>
> Why can't you define a "set of attributes" as a relation? I'm thinking
> that an empty relation (one with no tuples) has exactly the same
> information content as a "set of attributes". If you do that, why can't
> you say,
>
> PROJECT <relation>, <empty relation> -> <relation>
>
> Or have I violated some other aspect of the formalism?

What you describe is exactly the approach the Tropashko algebra takes. (Although it's just a specific case of the more general inner union operator, where one of the operands is empty.)

Marshall Received on Fri Aug 18 2006 - 00:51:21 CDT