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

Steinþór Steingrímsson, Örvar Kárason, Hrafn Loftsson


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
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)
Copy Citation:
PDF:
https://preview.aclanthology.org/ingestion-script-update/R19-1133.pdf
Code
 steinst/ABLTagger