| Approach | Counting the number of matched dependencies is essentially a simplified tree kernel for QA (e.g., see (Moschitti et al., 2007)) matching only trees of depth 2. |
| Approach | Experiments with full dependency tree kernels based on several variants of the convolution kernels of Collins and Duffy (2001) did not yield improvements. |
| Approach | We conjecture that the mistakes of the syntactic parser may be amplified in tree kernels , which consider an exponential number of sub-trees. |