Unsupervised Grammar Induction with Depth-bounded PCFG
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There has been recent interest in applying cognitively or empirically motivated bounds on recursion depth to limit the search space of grammar induction models (Ponvert et al., 2011; Noji and Johnson, 2016; Shain et al., 2016). This work extends this depth- bounding approach to probabilistic context- free grammar induction (DB-PCFG), which has a smaller parameter space than hierar- chical sequence models, and therefore more fully exploits the space reductions of depth- bounding. Results for this model on grammar acquisition from transcribed child-directed speech and newswire text exceed or are com- petitive with those of other models when eval- uated on parse accuracy. Moreover, gram- mars acquired from this model demonstrate a consistent use of category labels, something which has not been demonstrated by other ac- quisition models.
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