construction workers are working on beams.
construction workers building a ceiling
Just because construction workers are working on beams, it cannot be assumed that they are building a ceiling.
exists e1 x1 x2 x3.(on(e1,x3) & n_beam(x3) & Actor(e1,x1) & v_work(e1) & n_worker(x1) & of(x1,x2) & n_construction(x2))
exists e1 x1 x2 x3.(Theme(e1,x3) & Actor(e1,x1) & v_build(e1) & n_ceiling(x3) & n_worker(x1) & of(x1,x2) & n_construction(x2))