Relational Algebra Join This rule represents the relational algebra (binary) join operator. It takes two input relations and a join expression and outputs a relation that is the subset of tuples in the cartesian product of the input relations that satify the join expression. Join("r(x, y)", "s(u, v)", "y = u", "j(x, y, u, v)") Join("r(x, y)", "s(u, v)", "x > u ^ y <= u", "j(x, y, u, v)")