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Assessing Arabic Weblog Credibility via Deep Co-learning

Paper · 2019 · Chadi Helwe, Shady Elbassuoni, Ayman Al Zaatari et al.

Summary

The paper tackles automatic credibility assessment of Arabic blog posts when labeled data is very scarce. The only public resource is the crowdsourced corpus of Al Zaatari et al. (2016), with 268 posts. Each post is marked credible, fairly credible or not credible, and the posts cover topics such as regional wars and elections.

To work around this, the authors adapt Blum and Mitchell's co-training to neural networks and call the result deep co-learning. Two CNN classifiers look at the text differently: one uses CBOW word embeddings and the other uses character-level embeddings. Both start from the small labeled set. Each round, each model labels a random sample of unlabeled posts, and its most confident predictions are added to the other model's training data. A round's changes are kept only if an averaged ensemble of the two models scores higher F1 on a validation set.

On the test split, co-learning reaches F1 0.63. It beats a TF-IDF SVM, the single word and char CNNs, and their plain ensemble. This shows that semi-supervision can make deep models usable even with only a few hundred labeled examples.

Key points

  • Data: the Al Zaatari et al. (2016) Arabic blog credibility corpus (268 posts, crowdsourced three-way labels), plus a collected pool of unlabeled blog posts.
  • Models: a Word-CNN on CBOW embeddings and a Char-CNN on character embeddings. Both use dropout 0.2 and batch normalization between hidden layers, and are trained for 500 epochs with batch size 16 using Adagrad.
  • Co-learning setup: 50 iterations, each taking about 24 hours of retraining. Each round samples 1000 unlabeled items, and the top-50 scored items go to the opposite model.
  • Test F1 scores:
    • SVM TF-IDF (C=5): 0.57
    • Word-CNN: 0.52
    • Char-CNN: 0.54
    • Ensemble CNN: 0.50
    • Deep co-learning: 0.63
  • With so little data, the simple SVM beat every fully supervised deep model. Naively ensembling the two CNNs made results worse, not better.

Interesting ideas

  • I1. Two learners that see the data through different views (word tokens vs. characters) label unlabeled text for each other, so each one's errors are less likely to be repeated by its partner.
  • I2. Each augmentation step is a tentative proposal: machine-labeled additions are committed only if a held-out score improves, and otherwise discarded.
  • I3. Only a small top-k slice of the most confident automatic labels is transferred per round, rather than the whole sample. This keeps label noise low while the pool grows gradually.
  • I4. The evaluation includes a plain TF-IDF SVM and a naive ensemble, and these exposed that small-data deep models and simple averaging can underperform.
  • I5. Character-level input is used because it tolerates misspellings, emoticons and subword patterns that word embeddings miss.

For Mova

How these ideas could serve Mova, our small open language model — its files, stages and tests:

  • I1 (learn): Witness parsers with genuinely different inputs (the perceptron parser vs. gparse) could cross-supply silver trees, with each parser retrained only on the other's most confident parses.
  • I2 (learn): Self-induced repair rules or new silver batches could be accepted only when dev LAS or answer accuracy rises, giving a built-in guard against drift.
  • I3 (learn): Silver data agreed by witnesses could be admitted in small, confidence-ranked increments instead of in bulk.
  • I4 (learn): Every new learned component should be compared against a simple baseline and a trivial combination, as a negative control, before its gains are believed.
  • I5 (tokens): A character-based feature channel in the tagger or lemmatizer could handle noisy or out-of-vocabulary web tokens that a word lexicon misses.

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

 Fields, topics and concepts

Cite

Cite as Chadi Helwe, Shady Elbassuoni, Ayman Al Zaatari and Wassim El-Hajj. 2019. Assessing Arabic Weblog Credibility via Deep Co-learning. Proceedings of the Fourth Arabic Natural Language Processing Workshop.

The paper itself, not this page. BibTeX from the library's record of the work. DOI 10.18653/v1/w19-4614

@inproceedings{helwe2019assessing,
  title = {{Assessing Arabic Weblog Credibility via Deep Co-learning}},
  author = {Chadi Helwe, Shady Elbassuoni, Ayman {Al Zaatari} and Wassim El-Hajj},
  booktitle = {Proceedings of the Fourth Arabic Natural Language Processing Workshop},
  year = {2019},
  doi = {10.18653/v1/w19-4614},
  url = {https://doi.org/10.18653/v1/w19-4614}
}

References

18 references, 4 of them with a card of ours. ↗ leads to the work, «find» searches for one we have no id for yet.

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