We design a classifier based on SVMs and different kernels applied to several forms of question and answer representations: (1) linear kernels on the bag-of-words (BOW) or bag-of-POS-tags (POS) features, (2) the String Kernel (SK) (Shawe-Taylor and Cristianini, 2004) on word sequences (WSK) and POStag sequences (POSSK), (3) the Syntactic Tree Kernel (STK) (Collins and Duffy, 2002) on syntactic parse trees (PTs), (4) the Shallow Semantic Tree Kernel (SSTK) (Moschitti et al., 2007) and the Partial Tree Kernel (PTK) (Moschitti, 2006) on PASs.
pOS-tag sequences and pAS trees used with SK and pTK yield to two innovative kernels, i.e.