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Mikito Harakiri wrote:
> The proof of proposition 8.2.2 (page 164, the Alice book) begins with
> observation that given three sets of attributes X, Y and Z such that
> set Z complements sets X an Y in the relation header of the relalation
> I, the pi_XY(I) /\ pi_XZ(I) is always a superset of I. Is it obvious?
>
> In RL we do it in couple of steps:
>
> (XY \/ I) /\ (XZ \/ I) <= I ?
> ...
Question - in the RL approach, if pi_XY(I) is (XY \/ I), what does XY stand for? (eg., if XY isn't a projection, is it a 'bag'?)
BTW, 8.2.2 seems to be Heath's theorem, but Alice book doesn't seem to mention that.
p Received on Sat Apr 29 2006 - 10:17:14 CDT