Re: RA with MV attributes
Date: 20 Jan 2007 06:39:39 -0800
Message-ID: <1169303979.635668.78300_at_s34g2000cwa.googlegroups.com>
paul c wrote:
> David wrote:
> > paul c wrote:
> >
> >>David wrote:
> >>
> >>>paul c wrote:
> >>>...
> >>>
> >>>>I do think that once one has a definition it is important to proceed to
> >>>>positioning it in the scheme of things, for example is this a physical
> >>>>approach for storing two relations in one or is it an attempt to promote
> >>>>three-valued logic or is it something else?
> >>>
> >>>
> >>>I'm interested in both its logical and physical aspects. It seems
> >>>best initially to focus mainly on the logical.
> >>>...
> >>
> >>I could entertain this if the motive were to formalize a physical
> >>storage scheme. But I don't see anything logical about presenting to a
> >>user the inference that fred and bill own an empty set of cars that are
> >>green
> >
> >
> > That's an incorrect inference. That's not what a tuple means. If you
> > have the tuple
> >
> > Names = {Fred, Bill}, Cars = {}, CarColour = {green}
> >
> > Then you are meant to read out propositions by taking the cross product
> > of the sets. The cross product is of course empty.
> > ...
>
> Try telling that to a user who can see with his own eyes that the system
> is telling him that Fred and Bill stand in some relation to green cars
> and then explain to him that there is no relation in this case, because
> he is looking at something called a "join" that some other user created!
> (Then he will ask you what does join mean and the boss in frustration
> will renew your contract for another year.)
Obviously (end) users shouldn't look directly at a full outer join result.
Please read my recent post to Marshall. I describe an interesting relationship between outer and inner joins. Keep in mind the idea that tuples containing empty sets disappear in the mapping between tuples and propositions. Received on Sat Jan 20 2007 - 15:39:39 CET