Re: Relational Lattice, what is it good for?

vc wrote:
> Marshall Spight wrote:
> [...]
>
> That does not make any obvious sense. What is '(a, b, ab)' ? Is it
> the union of sets of attributes [of their respective relations] or
> something else ? You did not define the expression.

Under Conventions, I wrote:

"Sets of attributes are given with lower case letters, according to which relations these attributes appear in. Thus, (ab) is the set of attributes that are common to A and B. This set may be empty. The letters of the name are normalized to be in alphabetical order."

So '(a, b, ab)' contains all the attributes that are only in A, all the attributes that are only in B, and all the attributes that in in both A and B.

HTH Marshall Received on Sat Feb 18 2006 - 00:55:49 CET