Re: Thinking about MINUS
From: J M Davitt <jdavitt_at_aeneas.net>
Date: Mon, 08 Jan 2007 11:10:16 GMT
Message-ID: <sEpoh.9712$SJ3.2793_at_tornado.ohiordc.rr.com>
>
>
> While thinking about this, I stumbled on the following article that
> might be of interest:
>
> http://en.wikipedia.org/wiki/Relation_composition
>
> /Lennart
>
> [...]
>
Date: Mon, 08 Jan 2007 11:10:16 GMT
Message-ID: <sEpoh.9712$SJ3.2793_at_tornado.ohiordc.rr.com>
Lennart wrote:
> Bob Badour wrote:
> [...]
>
>>Right now, we are at the level of using INTERSECT as an analog to AND. >>Join is an extension of INTERSECT, and I am not yet clear how our >>discussion extends to JOIN yet. >>
>
>
> While thinking about this, I stumbled on the following article that
> might be of interest:
>
> http://en.wikipedia.org/wiki/Relation_composition
>
> /Lennart
>
> [...]
>
That's relation algebra and is different from relational algebra. It is interesting, though, that there are so many very similar systems which are just different enough to be different. It makes me think (hope?) that a "unifying theory" will one day emerge.
Darwen has defined a relational composition operation; he calls it COMPOSE. Received on Mon Jan 08 2007 - 12:10:16 CET