(Collins and Duffy, 2002;Kudo and Matsumoto, 2003;Cumby and Roth, 2003;Shen et al., 2003;Moschitti and Bejan, 2004;Culotta and Sorensen, 2004;Kudo et al., 2005;Toutanova et al., 2004;Kazama and Torisawa, 2005;Zhang et al., 2006;.
in question classification, tree kernels, e.g.