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Multilingual Language Processing From Bytes

Paper · 2016 · Dan Gillick, Cliff Brunk, Oriol Vinyals et al.

Summary

The paper asks whether text annotation can work without the usual NLP pipeline of tokenization, sentence splitting and language-specific preprocessing. The authors propose Byte-to-Span (BTS), a sequence-to-sequence LSTM. It reads a text segment as raw UTF-8 bytes and then outputs annotations as a series of separate symbols: a start offset, a length and a label, ending with STOP. The input alphabet is only 256 byte values plus a few special symbols, so the model stays very small (about a million parameters). A single network can also be trained on many languages at once. The authors test it on POS tagging in 13 languages and on NER in English, German, Spanish and Dutch, using only the provided training data. The joint multilingual model matches or beats earlier systems that are limited to the same data. It also outperforms same-sized BTS models trained on each language alone. The work matters because it shows that bytes can act as a shared cross-lingual representation. This removes per-language engineering and yields compact standalone taggers.

Key points

  • On NER, the single BTS model trained on all four languages scores 86.50 F1 (en), 76.22 (de), 82.95 (es) and 82.84 (nl). The per-language BTS* models score lower: 84.57, 72.08, 81.83 and 78.08.
  • Byte-dropout randomly replaces input bytes with a DROP symbol. Combined with standard dropout, it raises average NER F1 from 74.75 (vanilla) to 78.76 (dropout) and then to 82.13. Average POS accuracy over 13 languages rises from 94.78 to 95.35 and then to 95.85.
  • Depth helps more than width. With 320 units, NER F1 climbs from 76.15 with one layer to 82.13 with four layers. Doubling the width to 640 at depth 4 adds almost nothing (82.18).
  • The encoder and decoder share one set of LSTM weights without losing quality. Adding attention did not improve NER, although training converged faster.
  • A tSNE plot of the hidden state before NER label prediction shows clusters grouped by label rather than by language.

Interesting ideas

  • I1. Bytes as a universal input. Feeding raw UTF-8 bytes avoids tokenizers and per-language vocabularies. This could suit mixed-script or code-mixed text, such as Ukrainian–Russian–English data, where tokenization is messy.
  • I2. Split structured outputs into a sequence. Predicting start, length and label as three consecutive outputs keeps the output vocabulary small, and the authors report better and faster training than with the combined triple space. The same trick could apply to other span-style tasks that would otherwise need a BIO scheme or a huge label set.
  • I3. Input-noise regularization (byte-dropout). Corrupting random input symbols works like adding noise to audio or blurring images, and it gave large gains here. It is cheap to add to any character- or byte-level model.
  • I4. Diagnose shared representations through architecture and visualization. The authors compare the gains from depth versus width and inspect the hidden states with tSNE to check whether a multilingual model separates languages or learns shared abstractions. This is a reusable way to audit multilingual models.
  • I5. Be aware of the precision/recall asymmetry. A model that only emits spans lets you raise precision by thresholding the product of the span's probabilities, but offers no obvious way to raise recall. This is worth knowing before choosing a generative span output for tasks where recall matters.

Our summary of the paper, in our own words — not its text. The work belongs to its authors; read it at the links above.

 Institutions

 Fields, topics and concepts

Cite

Cite as Dan Gillick, Cliff Brunk, Oriol Vinyals and Amarnag Subramanya. 2016. Multilingual Language Processing From Bytes. Proceedings of the 2016 Conference of the North American Chapter of the Association for Computational Linguistics: Human Language Technologies.

The paper itself, not this page. BibTeX from the library's record of the work. DOI 10.18653/v1/n16-1155

@inproceedings{gillick2016multilingual,
  title = {{Multilingual Language Processing From Bytes}},
  author = {Dan Gillick, Cliff Brunk, Oriol Vinyals and Amarnag Subramanya},
  booktitle = {Proceedings of the 2016 Conference of the North American Chapter of the Association for Computational Linguistics: Human Language Technologies},
  year = {2016},
  doi = {10.18653/v1/n16-1155},
  url = {https://doi.org/10.18653/v1/n16-1155}
}

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