Augmenting a BiLSTM Tagger with a Morphological Lexicon and a Lexical Category Identification Step

Steinþór Steingrímsson, Örvar Kárason, Hrafn Loftsson

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Abstract
Previous work on using BiLSTM models for PoS tagging has primarily focused on small tagsets. We evaluate BiLSTM models for tagging Icelandic, a morphologically rich language, using a relatively large tagset. Our baseline BiLSTM model achieves higher accuracy than any other previously published tagger, when not taking advantage of a morphological lexicon. When we extend the model by incorporating such data, we outperform the earlier state-of-the-art results by a significant margin. We also report on work in progress that attempts to address the problem of data sparsity inherent to morphologically detailed, fine-grained tagsets. We experiment with training a separate model on only the lexical category and using the coarse-grained output tag as an input into to the main model. This method further increases the accuracy and reduces the tagging errors by 21.3% compared to previous state-of-the-art results. Finally, we train and test our tagger on a new gold standard for Icelandic.
Anthology ID:
R19-1133
Volume:
Proceedings of the International Conference on Recent Advances in Natural Language Processing (RANLP 2019)
Month:
September
Year:
2019
Address:
Varna, Bulgaria
Editors:
Ruslan Mitkov, Galia Angelova
Venue:
RANLP
SIG:
Publisher:
INCOMA Ltd.
Note:
Pages:
1161–1168
Language:
URL:
https://aclanthology.org/R19-1133
DOI:
10.26615/978-954-452-056-4_133
Bibkey:
Cite (ACL):
Steinþór Steingrímsson, Örvar Kárason, and Hrafn Loftsson. 2019. Augmenting a BiLSTM Tagger with a Morphological Lexicon and a Lexical Category Identification Step. In Proceedings of the International Conference on Recent Advances in Natural Language Processing (RANLP 2019), pages 1161–1168, Varna, Bulgaria. INCOMA Ltd..
Cite (Informal):
Augmenting a BiLSTM Tagger with a Morphological Lexicon and a Lexical Category Identification Step (Steingrímsson et al., RANLP 2019)
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PDF:
https://preview.aclanthology.org/teach-a-man-to-fish/R19-1133.pdf
Code
 steinst/ABLTagger
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