As such most prior work for learning SCFGs has relied on inference algorithms that were heuristically constrained or biased by word-based alignment models and small experiments (Wu, 1997;Zhang et al., 2008;Blunsom et al., 2009;Neubig et al., 2011).
to these previous attempts, our SCFG model scales to large datasets (over 1.3M sentence pairs) without imposing restrictions on the form of the grammar rules or otherwise constraining the set of learnable rules (e.g., with a word alignment).