A man is operating a piece of machinery.
The machinist is doing his job.
A man operating machinery does not necessarily imply a machinist or that he is doing his job.
exists e1 x1 x2 x3.(Theme(e1,x2) & Actor(e1,x1) & v_operate(e1) & of(x2,x3) & n_machinery(x3) & n_piece(x2) & n_man(x1))
exists e1 x1 x2.(n_job(x2) & of(x2,x1) & n_male(x1) & n_machinist(x1) & Theme(e1,x2) & Actor(e1,x1) & v_do(e1))