Syntactic Features for Evaluation of Machine Translation
What it is about
The paper adds syntax to n-gram evaluation. The headword-chain metric (HWCM) matches the head-modifier paths of the reference against the hypothesis. The subtree metric (STM) matches constituent subtrees, and a dependency subtree variant (DSTM) matches head subtrees. All of them need a parser on the hypothesis. At sentence level, most syntactic metrics predict fluency better than BLEU, and HWCM predicts overall sentence judgments better too. At corpus level the kernel-based subtree metric reaches a correlation of about 0.88 with human overall judgments on the 2005 test systems, against about 0.78 for BLEU at its best n-gram length. The authors note that the kernel metric is weak at sentence level, so the two levels can disagree.
Ideas
- I1. Headword-chain matching on meta trees: take the head-modifier chains of the reference's trees, read by the same reader, and check that each chain appears in the output's trees in the same order. This measures open problem 3, whether the encoder writes trees.
- I2. Report sentence-level and verse-level-aggregated scores separately, as the paper shows they can disagree. A delta that raises the corpus score but lowers the per-verse agreement is flagged.
- I3. A syntactic fluency check on the encoder output, computed as chain matches, to catch order errors that bag-of-concept scores miss.
For Mova
The places are tools/roundtrip (UD trees) and en/src/lin.rs (order). Mova does not need a parser on the output: the paper's cost is the parsing of noisy MT, and Mova can compare meta trees built from the references instead.
Cite
@inproceedings{liu2005syntactic,
title = {{Syntactic Features for Evaluation of Machine Translation}},
author = {Liu, Ding and Gildea, Daniel},
booktitle = {Proceedings of the ACL Workshop on Intrinsic and Extrinsic Evaluation Measures for Machine Translation and/or Summarization},
year = {2005},
url = {https://aclanthology.org/W05-0904/}
}References
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