Re: Very simple question to relational theorists.

On Tuesday, September 11, 2012 3:51:37 AM UTC-7, Evgeniy Grigoriev wrote:

> "So if the wff R(A,B,...) denotes the predicate for R then the wff for R RENAME A TO N is R(N,B,...). If the wff S(X,Y,...,A,...) denotes the predicate for S then the wff for (R JOIN S) RENAME A TO N is R(N,B,...) AND S(X,Y,...,N,...). "

> To be correst, let me first ask you about virtual view which is (I hope) possible for you. Can I define some virtual view Q as result of (R JOIN S)? Ok, "the wff for for (R JOIN S) RENAME A TO N is R(N,B,...) AND S(X,Y,...,N,...)" but was is name "Q" here?

Do you mean, what is a wff for the predicate of Q?

Q has an associated relational expression R JOIN S. So a wff for Q's associated predicate is R(A,B,...) AND S(X,Y,...,A,...). This is because predicate-of-(R JOIN S) is predicate-of-R AND predicate-of-S. (We were given wffs for these two predicates.)

philip Received on Thu Sep 13 2012 - 12:57:10 CEST