Beyond English-Only Reading Comprehension

Experiments in Zero-Shot Multilingual Transfer for Bulgarian

Introduction

Recently, reading comprehension models achieved near-human performance on large-scale datasets such as SQuAD, CoQA, MS Macro, RACE, etc. This is largely due to the release of pre-trained contextualized representations such as BERT and ELMo, which can be fine-tuned for the target task. Despite those advances and the creation of more challenging datasets, most of the work is still done for English. Here, we study the effectiveness of multilingual BERT fine-tuned on large-scale English datasets for reading comprehension (e.g., for RACE), and we apply it to Bulgarian multiple-choice reading comprehension. We propose a new dataset containing 2,221 questions from matriculation exams for twelfth grade in various subjects -history, biology, geography and philosophy-, and 412 additional questions from online quizzes in history. While the quiz authors gave no relevant context, we incorporate knowledge from Wikipedia, retrieving documents matching the combination of question + each answer option.

Our academic paper which describes the approach, the dataset, and the results in detail, can be found here: https://arxiv.org/abs/1908.01519

Dataset

Our goal is to build a task in a low-resource language, such as Bulgarian, as close as possible to the multiple-choice reading comprehension in a high-resource language such as English. The dataset can be downloaded from this link.

Domain	#QA-paris	#Choices	Len Question	Len Options	Vocab Size
12th Grade Matriculation Exam
Biology	437	4	10.44	2.64	2,414 (12,922)
Philosophy	630	4	8.91	2.94	3,636 (20,392)
Geography	612	4	12.83	2.47	3,239 (17,668)
History	542	4	23.74	3.64	5,466 (20,456)
Online History Quizzes
Bulgarian History	229	4	14.05	2.80	2,287 (10,620)
PzHistory	183	3	38.89	2.44	1,261 (7,518)
Total	2,633	3.93	15.67	2.89	13,329 (56,104)

Evaluation

To evaluate the models we have built an evaluation script, allowing easy performance measrument of the predicted results. To run the evaluation, use:

python evaluate.py data/bg_rc-v1.0.json experiments/preds.json

The prediction file should be in the following format:

{
  "id": "predicted_answer",
  ...
  "id": "predicted_answer"
}

Running the model

Filling ElasticSearch with Wikipedia

Create wikidump

First, we need to download a Wikipedia database dump for Bulgarian. (e.g. https://ftp.acc.umu.se/mirror/wikimedia.org/dumps/bgwiki/20190501/bgwiki-20190501-pages-meta-current.xml.bz2)

Next step is to convert the xml into well-structured JSON with WikiExtractor.

python WikiExtractor.py ---output bgwiki.json --json /path/to/bgwiki-*-current.xml 

This should produce a folder with the following format: AA, AB,..., ZZ

Fill the index

Download ES (Tested with 7.0.1) from the official web site.

Start an instance:

./elasticsearch-7.0.1/bin/elasticsearch

Create ElasticSearch filler config file:

{
   "host":"localhost",
   "port":"9200",
   "index_name":"bgwiki_test",
   "batch_size":10000,
   "es_schema":{
      "settings":{
         "max_ngram_diff":3,
         "analysis":{
            "analyzer":{
               "my_analyzer":{
                  "tokenizer":"my_tokenizer"
               }
            },
            "tokenizer":{
               "my_tokenizer":{
                  "type":"ngram",
                  "min_gram":1,
                  "max_gram":3,
                  "token_chars":[
                     "whitespace",
                     "punctuation"
                  ]
               }
            }
         }
      },
      "mappings":{
         "properties":{
            "title":{
               "type":"text",
               "fields":{
                  "ngram":{
                     "type":"text",
                     "analyzer":"my_analyzer"
                  },
                  "bulgarian":{
                     "type":"text",
                     "analyzer":"bulgarian"
                  }
               }
            },
            "passage":{
               "type":"text",
               "fields":{
                  "ngram":{
                     "type":"text",
                     "analyzer":"my_analyzer"
                  },
                  "bulgarian":{
                     "type":"text",
                     "analyzer":"bulgarian"
                  }
               }
            },
            "page":{
               "type":"long"
            },
            "isbn":{
               "type":"text"
            },
            "timestamp":{
               "type":"date",
               "format":"strict_date_optional_time||epoch_millis"
            }
         }
      }
   }
}

Fill the inverted index:

python fill_elastic.py --wiki_path /PATH/TO/WIKI_EXTRACTOR_DIRS --es_config_file ./configs/bgwiki.json 

Running the prediction pipeline

The code for the prediction pipeline is available as a Jupyter notebook bg_reason_BERT/WikipediaDocumentMatcher.ipynb.

Cite

The paper is presented at RANLP 2019. Read the paper at: ACL Anthology, or Arxiv:

Please, cite as:

@inproceedings{hardalov-etal-2019-beyond,
    title = "Beyond {E}nglish-Only Reading Comprehension: Experiments in Zero-shot Multilingual Transfer for {B}ulgarian",
    author = "Hardalov, Momchil  and
      Koychev, Ivan  and
      Nakov, Preslav",
    booktitle = "Proceedings of the International Conference on Recent Advances in Natural Language Processing",
    series = "RANLP~'19",
    year = "2019",
    address = "Varna, Bulgaria",
    url = "https://www.aclweb.org/anthology/R19-1053",
    doi = "10.26615/978-954-452-056-4_053",
    pages = "447--459",
}