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Assessing the impact of OCR noise on multilingual event detection over digitised documents

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Abstract

Event detection is a crucial task for natural language processing and it involves the identification of instances of specified types of events in text and their classification into event types. The detection of events from digitised documents could enable historians to gather and combine a large amount of information into an integrated whole, a panoramic interpretation of the past. However, the level of degradation of digitised documents and the quality of the optical character recognition (OCR) tools might hinder the performance of an event detection system. While several studies have been performed in detecting events from historical documents, the transcribed documents needed to be hand-validated which implied a great effort of human expertise and manual labour-intensive work. Thus, in this study, we explore the robustness of two different event detection language-independent models to OCR noise, over two datasets that cover different event types and multiple languages. We aim at analysing their ability to mitigate problems caused by the low quality of the digitised documents and we simulate the existence of transcribed data, synthesised from clean annotated text, by injecting synthetic noise. For creating the noisy synthetic data, we chose to utilise four main types of noise that commonly occur after the digitisation process: Character Degradation, Bleed Through, Blur, and Phantom Character. Finally, we conclude that the imbalance of the datasets, the richness of the different annotation styles, and the language characteristics are the most important factors that can influence event detection in digitised documents.

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Notes

  1. https://www.ldc.upenn.edu/sites/www.ldc.upenn.edu/files/english-events-guidelines-v5.4.3.pdf.

  2. https://catalog.ldc.upenn.edu/LDC2006T06.

  3. However, even though the reported results were better than the model that we experiment within this study, the CNN-based model in [3] that utilises a wide range of convolutional windows, requires a considerable amount of memory resources and therefore could not be put in practice.

  4. https://framenet.icsi.berkeley.edu/fndrupal/.

  5. The authors utilised the Adobe Acrobat Pro DC OCR software, version 2015. However, the system has long been outdated.

  6. The authors made available the trained models on GitHub: https://github.com/dhfbk/Histo.

  7. https://catalog.ldc.upenn.edu/LDC2006T06.

  8. We remind here that this sub-task is not treated in this study. Because event detection is already challenging, we base our experiments only on ED.

  9. This process is done by using the interlingual links coming from English infectious diseases Wikipedia pages.

  10. If no location matches the previous rules, the system assumes that the event takes place in the country of the “source” metadata (Implicit Location Rule [33]).

  11. https://imagemagick.org.

  12. https://docs.microsoft.com/en-us/typography/font-list/arial-unicode-ms.

  13. https://github.com/tesseract-ocr/tesseract.

  14. We assume that using different major versions of Tesseract (e.g. from 3.x to 4.x) may affect our results since the OCR engine has changed considerably according to the changelog. However, since we chose the last version available, it might be too tedious and time-consuming to perform experiments with different Tesseract versions in the light of a different OCR engine.

  15. We noticed the fact that the batch size affects the Adam optimiser [60], and thus our choice of 256, which performed the best on the validation set.

  16. This is also observed in Fig. 7.

  17. We designate this a limitation in our set-up and we detail it in Sect. 8.3.

  18. While Bidirectional Encoder Representations from Transformers (BERT) had a major impact in the NLP community, its ability to handle noisy inputs is still an open question [62] or at least requires the addition of complementary methods [44, 52].

  19. https://github.com/tesseract-ocr/tesseract.

  20. The ACE 2005 dataset is available under a paid license and thus, we cannot make it available.

  21. https://zenodo.org/record/3709617.

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Acknowledgements

This work has been supported by the European Union’s Horizon 2020 research and innovation programme under grants 770299 (NewsEye) and 825153 (EMBEDDIA), and by the ANNA and Termitrad projects funded by the Nouvelle-Aquitaine Region.

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Emanuela Boros: Conceptualization, Methodology, Software, Formal analysis, Investigation, Data Curation, Writing. Nhu Khoa Nguyen: Conceptualization, Methodology, Software, Formal analysis, Investigation, Writing. Gaël Lejeune: Conceptualization, Methodology, Supervision, Writing - review & editing. Antoine Doucet: Funding acquisition, Conceptualization, Methodology, Project administration, Validation, Supervision, Writing - review & editing.

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Correspondence to Emanuela Boros.

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Boros, E., Nguyen, N.K., Lejeune, G. et al. Assessing the impact of OCR noise on multilingual event detection over digitised documents. Int J Digit Libr 23, 241–266 (2022). https://doi.org/10.1007/s00799-022-00325-2

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