Structured Prediction of Sequences and Trees using Infinite Contexts
Table 2: Syntactic parsing results for the Penn. treebank, showing labelled F-Measure (F1) and exact bracketing match (ACC).
['[BOLD] Syntactic Parser', 'all F1', 'all ACC', '≤40 F1', '≤40 ACC']
For syntactic parsing, we use the Penn. treebank We used the standard data splits for training and testing (train sec 2-21; validation sec 22; test sec 23). We followed Petrov et al. preprocessing steps by right-binarizing the trees and replacing words with count≤1 in the training sample with generic unknown word markers representing the tokens’ lexical features and position. We note that the A* parser becomes less effective (even with a large beam size) for this task, which we attribute to the large search arising for the large grammar and long sentences. Our best results are achieved by MCMC, demonstrating the effectiveness of MCMC in large search spaces.