Jun'ichi Kazama Kentaro Torisawa Speeding up Training with Tree Kernels for Node Relation Labeling. 2005 conf/naacl/2005 HLT/EMNLP http://acl.ldc.upenn.edu/H/H05/H05-1018.pdf db/conf/naacl/naacl2005.html#KazamaT05