%
% Understanding Relational Database Query Languages, S. W. Dietrich, Prentice Hall, 2001.
%
%---------------------------------------------------------------------------------------------------------------------------
%        DOMAIN RELATIONAL CALCULUS (DRC)
%---------------------------------------------------------------------------------------------------------------------------
%  Abstract Division Example
%
%  abTable(a,b)
%       primary key (a, b)
%  bTable(b)
%       primary key (b)
%---------------------------------------------------------------------------------------------------------------------------

universalDivision :=
    { A | abTable(A, _) and (forall B) (not bTable(B) or abTable(A,B) ) }; 

forallExistsEquivalence :=
{ A | abTable(A, _) and not (exists B) (not (not bTable(B) or abTable(A,B) ) )};

existentialDivision :=
    { A | abTable(A, _) and not (exists B) (bTable(B) and not abTable(A,B)) };