Parsing of Czech: Between Rules and Stats

​IA161 NLP in Practice Course, Course Guarantee: Aleš Horák

Prepared by: Miloš Jakubíček

State of the Art

References

1. Zhang, Y., Zhou, H., & Li, Z. (2020). Fast and Accurate Neural CRF Constituency Parsing. arXiv preprint arXiv:2008.03736.
2. Qi, P., Dozat, T., Zhang, Y., & Manning, C. D. (2019). Universal dependency parsing from scratch. arXiv preprint arXiv:1901.10457.
3. Straka, M., Straková, J., & Hajič, J. (2019). Czech Text Processing with Contextual Embeddings: POS Tagging, Lemmatization, Parsing and NER. In International Conference on Text, Speech, and Dialogue (pp. 137-150). Springer, Cham.
4. Baisa, V. and Kovář, V. (2014). Information extraction for Czech based on syntactic analysis. In Vetulani, Z. and Mariani, J., editors,Human Language Technology Challenges for Computer Science and Linguistics, pages 155–165. Springer International Publishing.

Practical Session

We will develop/adjust the grammar of the SET parser.

1. Download the SET parser with evaluation dataset

   wget https://nlp.fi.muni.cz/trac/research/chrome/site/bigdata/ukol_ia161-parsing.zip
   

2. Unzip the downloaded file

   unzip ukol_ia161-parsing.zip
   

3. Go to the unziped folder

   cd ukol_ia161-parsing
   

4. Choose the language you want to work with. The default is Czech (cs) which can be changed to English (en) via editing Makefile:

   nano Makefile
   

   change the first line to

   LANGUAGE=en
   

5. Test the prepared program that analyses 100 selected sentences

   make set_trees
   make compare
   

   The output should be

   ./compare_dep_trees.py data/trees/pdt2_etest data/trees/set_pdt2_etest-sel100
   UAS =  66.1 %
   

   You can see detailed evaluation (sentence by sentence) with

   make compare SENTENCES=1
   

   You can watch differences for one tree with

   make diff SENTENCE=00009
   

   Exit the diff by pressing q.
   You may inspect the tagged vertical text with

   make vert SENTENCE=00009
   

   You can watch the two trees with (python3-tk must be installed in the system)

   make view SENTENCE=00009
   

   For remote tree view, you may run

   make html SENTENCE=00009
   

   And point your browser to the html/index.html file.
   You can extract the text of the sentence easily with

   make text SENTENCE=00009
   

   English translation of the Czech sentences can be obtained via

   make texttrans SENTENCE=00009
   

6. Look at the files:
   • data/vert/pdt2_etest or ud21_gum_dev - 100 input sentences in vertical format. The tag format is the Prague Dependency Treebank ​positional tagset for Czech and the ​Penn Treebank tagset for English
   • data/trees/pdt2_etest or ud21_gum_dev - 100 gold standard dependency trees from the Prague Dependency Treebank or the Universal Dependencies GUM corpus
   • data/trees/set_pdt2_etest or set_ud21_gum_dev - 100 trees output from SET by running make set_trees
   • grammar-cs.set or grammar-en.set - the grammar used in running SET

Assignment

1. Study the ​SET documentation. The tags used in the Czech grammar are in the Brno tagset.
2. Develop better grammar - repeat the process:

   nano grammar.set # or use your favourite editor
   make set_trees
   make compare
   

   to improve the original UAS
3. Write the final UAS in grammar-cs.set or grammar-en.set

   # This is the SET grammar for Czech used in IA161 course
   # 
   # ===========   resulting UAS =  66.9 %  ===================
   

4. Upload your grammar-cs.set or grammar-en.set to the homework vault.