Re: Notions of Type
From: paul c <toledobythesea_at_oohay.ac>
Date: Fri, 18 Aug 2006 00:43:50 GMT
Message-ID: <a38Fg.416358$iF6.240557_at_pd7tw2no>
>
> Which theory:-?
>
> In classic RA they aren't.
>
> In D&D algebra they are. In relational lattice they are too.
>
Date: Fri, 18 Aug 2006 00:43:50 GMT
Message-ID: <a38Fg.416358$iF6.240557_at_pd7tw2no>
Aloha Kakuikanu wrote:
> paul c wrote:
>> Aloha Kakuikanu wrote: >>> Keith H Duggar wrote: >>>> Marshall wrote: >>>>> Very true. Of the various relational operators that have >>>>> been identified over the years, only a few, like union, >>>>> are really algebraic. >>> Except that union applies to relations of the same arity only. >> I thought that was only a practical restriction, ie., in theory, any >> relations can be unioned?
>
> Which theory:-?
>
> In classic RA they aren't.
>
> In D&D algebra they are. In relational lattice they are too.
>
I guess I meant D&D. Still, I thought the 'classic' version must have to allow for different headers in theory, even if not in practice, otherwise axioms like de Morgan's laws wouldn't be true. (When I read about the lattice's union, I was puzzled for the same reason.)
p Received on Fri Aug 18 2006 - 02:43:50 CEST