Effective Self-Training for Parsing
What it is about
Self-training of parsers was thought to fail because the parser's own errors are amplified. This paper shows that it works when the self-labelled trees come from a two-stage parser and reranker: the 50-best parses of 24 million unlabelled News sentences are reranked, and the reranker's best tree is added to the Wall Street Journal training data, with the two counts merged. Adding the parser's own best trees does not help, but adding the reranker's best trees lifts the first-stage parser from 90.3 to 91.0 F on section 22 at 750k added sentences, and the full system reaches 92.1 F on WSJ, a 12% error reduction. The gain levels off near 91.0 F as more sentences are added.
Ideas
- I1. en/src/parse.rs training on silver: label the school corpus with the teacher's trees, and separately keep only the trees that
treeagreeagrees with the independent parsers; measure LAS on EWT dev (cv) as the silver set grows, and stop where the curve flattens, as this paper does. - I2. en/src/ptag.rs and en/src/parse.rs: merge the counts of gold and silver events with a weight (for example 1 and 0.5) instead of equal weights, and measure LAS on EWT dev for both.
- I3. Keep a separate check of whether the silver set gains through the same features as the teacher's (the paper's own hypothesis): measure LAS on EWT dev with silver trees that the Mova parser itself chose, which should show less gain if that is the cause.
For Mova
The ideas touch the silver corpus in corpus/ and the agreement rules in tools/treeagree (src/rules.rs), and the training counts of en/src/parse.rs. The chapter that matters for the teacher-student setup is languages/en/37-register-and-variation, since the school corpus is not EWT. Measure first I1 on EWT dev, with the cv folds, and keep the EWT test for one run per release.
Cite
@inproceedings{mcclosky2006effective,
title = {{Effective Self-Training for Parsing}},
author = {McClosky, David and Charniak, Eugene and Johnson, Mark},
booktitle = {Proceedings of the Human Language Technology Conference of the NAACL, Main Conference},
year = {2006},
doi = {10.3115/1220835.1220855},
url = {https://doi.org/10.3115/1220835.1220855}
}References
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