Cardinality of relation with empty set of attributes is 1

Proof:
MVFD with empty antecedent, for example

{} -> {X} | {Y,Z}

claims that cardinality of the XYZ relation is the product of cardinalities of its projection onto the sets X and YZ of attributes.

Take {X} to be an empty set, then:
{} -> {} | {X,Y,Z}

holds trivially. Since projection to the entire set of attributes
{X,Y,Z} doesn't really change the relation, it follows that the other
relation in the MVFD decompostition should have cardianlity 1. Received on Mon Oct 02 2006 - 13:38:17 CDT