An older man with a graying beard, possibly a homeless person, sleeps on the grass in front of an ancient tree in a public park.
An old man is sleeping the grass.
In both sentences, an old man is described to be sleeping in the grass. The second sentence just has less detail.
exists e1 e2 s1 s2 s3 s4 x1 x2 x3 x4 x5 x6 x7.(n_grass(x4) & on(e2,x4) & in(x4,x5) & of(x5,x6) & in(x6,x7) & n_park(x7) & a_public(s4) & Theme(s4,x7) & n_tree(x6) & a_ancient(s3) & Theme(s3,x6) & n_front(x5) & Actor(e2,x1) & v_sleep(e2) & rel(x1,x3) & r_possibly(x3) & n_person(x3) & a_homeless(s2) & Theme(s2,x3) & with(x1,x2) & n_beard(x2) & Actor(e1,x2) & v_gray(e1) & n_man(x1) & r_more(s1) & a_older(s1) & Theme(s1,x1))
exists e1 s1 x1 x2.(n_grass(x2) & Theme(e1,x2) & Actor(e1,x1) & v_sleep(e1) & n_man(x1) & a_old(s1) & Theme(s1,x1))