Functional dependency is multivalued dependency
From: Mikito Harakiri <mikharakiri_nospaum_at_yahoo.com>
Date: 28 Apr 2006 09:18:06 -0700
Message-ID: <1146241086.922523.280790_at_v46g2000cwv.googlegroups.com>
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?
Date: 28 Apr 2006 09:18:06 -0700
Message-ID: <1146241086.922523.280790_at_v46g2000cwv.googlegroups.com>
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 ?
This is the same as
I /\ (XY \/ I) /\ (XZ \/ I) <= I
and the left side reduces to I by 2 applications of the absorption law.
That is about prioving the obvious part of the proposition. I'm stuck on the non-obvious part. Any ideas? Received on Fri Apr 28 2006 - 18:18:06 CEST