These DTs preserve structural information as the dot product between the DTs of two trees approximates the classical tree kernels T K as defined by Collins and Duffy (2002), that is, T K(t a , t b ) ≈ DT (t a ), DT (t b ) .
this function guarantees that two different subtrees have nearly orthonormal vectors (see (Zanzotto and Dell'Arciprete, 2012) for more details).