Shallow Discourse Parsing for Under-Resourced Languages: Combining Machine Translation and Annotation Projection
Summary
Training shallow discourse parsers requires large annotated corpora, and only English has one at sufficient scale: the Penn Discourse TreeBank (PDTB). The authors therefore build a German resource automatically. They machine-translate the English PDTB 2.0 (the CoNLL 2016 shared-task subset) into German and transfer its annotations onto the translation via word alignment. Unlike earlier projection work, which handled only explicit connectives, this approach transfers whole coherence relations, including arguments, senses and non-explicit types. Alignment comes from GIZA++, refined with Moses symmetrisation heuristics, and connective candidates are checked against the DiMLex lexicon. The result is GermanPDTB, a silver-standard corpus of German financial news. It is far larger than the existing gold German data and also yields new candidate entries for DiMLex. The authors analyse translation and projection errors, then test the corpus extrinsically: they train selected parser components on GermanPDTB and compare them with the same components trained on the gold English PDTB. The comparison figures are not included in the excerpt provided. The work matters because it offers a reusable recipe for any language with decent MT from English.
Key points
- Source corpus vs. German data: PDTB 2.0 has over 1M words and more than 40k relations. The largest gold German corpus, the Potsdam Commentary Corpus (PCC), has only 2,208 relations.
- Choice of MT system: Five systems were compared by BLEU on an OPUS news corpus (Google Translate, DeepL, Bing, Edinburgh NMT, Moses). DeepL (28.07) and Google (26.6) scored best. A 50-sentence manual check (Popovic et al., 2013) rated them as equal in quality. DeepL was chosen because its alignments recovered more explicit connectives.
- Alignment method: Six alignment variants were tested (intersection, union, grow, grow-diag, grow-diag-final, grow-diag-final-and) by matching aligned connectives against DiMLex. Intersection became the default because the authors prioritised precision over recall.
- Relations projected: Explicit (~43%), Implicit (~38%), EntRel (~12%) and AltLex (~2%) relations were projected. NoRel (~0.6%) was excluded.
Cited by
- GDTB: Genre Diverse Data for English Shallow Discourse Parsing across Modalities, Text Types, and Domains
- Investigating Explicitation of Discourse Connectives in Translation using Automatic Annotations
Cite
@inproceedings{sluytergathje2020shallow,
title = {{Shallow Discourse Parsing for Under-Resourced Languages: Combining Machine Translation and Annotation Projection}},
author = {Sluyter-Gäthje, Henny and Bourgonje, Peter and Stede, Manfred},
booktitle = {Proceedings of the Twelfth Language Resources and Evaluation Conference},
year = {2020},
url = {https://aclanthology.org/2020.lrec-1.131/}
}References
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