Learning Morphology with Morfette

What it is about

Morfette learns morphological tagging and lemmatization jointly from annotated corpora. Two modules, each a maximum entropy classifier, predict the morphological tags and the lemmas. A third module combines their predictions into a probability distribution over tag-lemma pairs for each sentence. Lemmatization is recast as classification: each class label encodes how a word form maps to its lemma, as a change of prefix and suffix. The system is tested on three morphologically rich languages, Romanian, Spanish and Polish, with no language-specific feature engineering. The lemma rules give a relative error reduction of 62% to 66.5% over a baseline for all words, and the paper reports that the baseline is clearly worse on unseen words.

Ideas

• I1. en/src/morph.rs: lemmatization as a class of edit rules (strip a suffix, add a suffix), learned from data/forms.tsv and data/lemmas.tsv, used only for forms that the dictionary does not contain. Measure lemma accuracy on the unseen forms of EWT test against the current rule set.
• I2. Report the lemma accuracy on unseen words separately, as the paper does, since the English dictionary hides this error on known words.
• I3. A joint score: add the tag-lemma pair probability of en/src/ptag.rs and the lemma rule, and keep the best pair. Measure joint accuracy on EWT test, and check that two runs give the same output.

For Mova

The code is en/src/morph.rs and en/src/ptag.rs, with the commands en morph-eval and en tag-eval. The chapter is 11. Nouns for plural lemmas and 13. Verbs for verb forms. The paper's languages are not English and its corpora are LREC data under NC, so use it only for the method and test on EWT test. Measure first with a two-fold check (en folds).

Cite

The paper itself, not this card. BibTeX from the library's record of the work. DOI 10.63317/46dhmje42wcr

@inproceedings{chrupala2008learning,
  title = {{Learning Morphology with Morfette}},
  author = {Chrupala, Grzegorz and Dinu, Georgiana and Genabith, Josef van},
  booktitle = {Proceedings of the Sixth International Conference on Language Resources and Evaluation (LREC'08)},
  year = {2008},
  doi = {10.63317/46dhmje42wcr},
  url = {https://doi.org/10.63317/46dhmje42wcr}
}

References

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