Re: atomic
Date: 3 Nov 2007 05:01:56 -0700
Message-ID: <1194054293.755942.219500_at_q3g2000prf.googlegroups.com>
On Nov 2, 6:28 am, paul c <toledobythe..._at_ooyah.ac> wrote:
> I'm wondering are there applications where RVA values that are "empty"
> make sense or are such values just a curious by-product of RVA's? If
> the latter, should they be suppressed or somehow prevented?
Note therefore that the last tuple actually maps to zero predicates.
So r1 |X| r2 is *interpreted* as
Name Car Colour
bill car1 red bill car4 red bill car2 green john car3 red fred car3 red
The MV approach suffers from a troubling non-uniqeness of representation. I don't know if this is really a problem or not.
BTW, in that thread Bob pointed out that a naive definition of projection gives the wrong answers. Clearly a correct definition of projection would be straightforward given the reinterpretation in single valued attributes.
I'm not sure whether the idea has any merit. It possibly could if one is faced with a problem domain with lots of missing information, and many, many 6NF predicates that would become painful to work with. In certain problem domains the space reduction could be significant. There are potential benefits for both the user and the DBMS implementation Received on Sat Nov 03 2007 - 13:01:56 CET