Indeed, the top-systems were built using Support Vector Machines (SVMs) trained with Tree Kernels (TKs), which were applied to a syntactic representation of question text (Filice et al., 2016Barrón-Cedeño et al., 2016).
nns-based models struggled to get good accuracy as (i) large training sets are typically not available 2 , and (ii) effectively exploiting full-syntactic parse information in nns is still an open issue.