Using the Penn Treebank to Evaluate Non-Treebank Parsers
What it is about
The question is how to compare a parser that was never trained on the Penn Treebank (NLPWin, built at Microsoft Research) with Treebank-trained parsers such as Charniak's, when the two attach modifiers in a different order and use different brackets. The authors score both on unlabelled precision and recall of maximal projections of heads (MPH), a bracket set that focuses on "maximal projections of heads" (p. 1). Head labels for the gold trees come from Charniak's head rules, plus a small set of reassignment rules; single-word brackets, the sentence bracket and punctuation are dropped, and unary nodes are flattened. On WSJ section 23, NLPWin reaches P 74.32 and R 74.25, and Charniak's parser P 86.18 and R 85.72. On the restricted Brown test BR1 the gap is smaller (NLPWin P 69.54, R 70.56; Charniak P 77.71, R 77.73). The authors argue that raw brackets would reward high PP attachment, and that a dependency tree with ordered dependents is isomorphic to an MPH tree, so the same metric could score dependency parsers.
Ideas
- I1.
tools/parsecmp: add an MPH score next to the labelled scores. In a UD tree, each word and all its dependents form one span, which is the same bracket the paper's MPH trees give, so the metric needs no head-rule set. Score theenoutput and the constituency runs already listed inparsecmp(stanza-con,benepar,supar-con) against the same Haiku reference, and check whether the MPH ranking of systems agrees with the LAS ranking. Non-projective trees give spans with gaps; report their count separately. - I2. Negative control for that metric: in a copy of the reference, move every PP from verb attachment to noun attachment by a fixed rule. MPH precision and recall must fall on the same sentences. A metric that stays flat under this change is not measuring attachment.
- I3. Bias check, as the paper warns about high attachment: on EWT test, count how often
enattaches a PP to the verb and to the noun, and how often gold does, and report the MPH score on the PP subset alone. This shows whether the SLM has the bias the paper describes, and in which direction.
For Mova
The chapters are 22. Phrases: noun, adjective, adverb and prepositional phrases (NP structure, PP attachment) and 21. The simple clause. The code is tools/parsecmp (the SYSTEMS and CONSTITUENCY lists) and en parse-eval. The Penn Treebank is LDC data under non-commercial terms: use it, if at all, for tests only, never in a release. The EWT measurements are CC BY-SA, so they are measurements, not material carried into a build.
Cite
@inproceedings{ringger2004using,
title = {{Using the Penn Treebank to Evaluate Non-Treebank Parsers}},
author = {Ringger, Eric K. and Moore, Robert C. and Charniak, Eugene and Vanderwende, Lucy and Suzuki, Hisami},
booktitle = {Proceedings of the Fourth International Conference on Language Resources and Evaluation (LREC'04)},
year = {2004},
url = {https://aclanthology.org/L04-1115/}
}References
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