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AlexU-AIC at Arabic Hate Speech 2022: Contrast to Classify

Paper · 2022 · Ahmad Shapiro, Ayman Khalafallah and Marwan Torki

Summary

The authors tackle the three-level Arabic hate speech shared task at OSACT5 2022, using tweets annotated by Mubarak et al. (2022). The levels are: is a tweet offensive, is an offensive tweet hate speech, and which of six hate categories it falls into. The training split is small (about 8.9k tweets) and heavily skewed, so fine-tuned transformers overfit easily.

The team compared AraBERT and MarBERT encoders and settled on MarBERTv2, whose pre-training on tweets matched the data. They tested three training regimes on top of Arabic-specific text normalisation:

  • plain classification fine-tuning,
  • contrastive learning with several loss variants,
  • multi-task learning, with an extra balanced corpus pooled from earlier Arabic offensive-language datasets.

In the final submission, sub-task A was handled by an ensemble of five models, while B and C relied on a multi-task model. It reached macro-F1 of 0.841, 0.817 and 0.476, far above majority baselines. The study is useful as a comparison of which training regime fits which degree of class imbalance.

Key points

  • The dataset has 12.7K tweets, split 70/10/20 into 8887 train, 1270 dev and 2541 test.
    • Labels: OFF/NOT OFF, HS/NOT HS, six HS classes (Race, Religion, Ideology, Disability, Social Class, Gender), plus vulgar and violent flags.
  • Imbalance is severe:
    • about 35.7% OFF and 10.8% HS in training;
    • roughly 89% of training tweets are NOT HS in sub-task C;
    • HS4 (Disability) has no training examples at all.
  • MarBERTv2 was preferred for two reasons: it was pre-trained on 1B Arabic tweets, and its vocabulary keeps 567 emoji. This mattered because all but 2 train/dev tweets contain emoji.
  • The BALANCED resource was assembled from OSACT2020, OffensEval2020 and other corpora, and was used only for multi-task learning.
    • Sub-task A: 19,906 examples.
    • Sub-task B: 4800 examples, compared with only 959 HS tweets in the original training data.
  • Final macro-F1 scores were 0.841 (A), 0.817 (B) and 0.476 (C), against majority baselines of 0.394, 0.472 and 0.135.
    • Pre-processing helped.
    • Contrastive training edged out plain fine-tuning only when imbalance was moderate.

Interesting ideas

  • I1. Before picking an encoder, the authors checked a surface property of the data (near-universal emoji) and chose a model whose vocabulary keeps it; they later learned emoji had been the anchors used to collect the corpus.
  • I2. They ran a per-subtask comparison of training regimes and found that the best regime depends on how skewed the labels are, with contrastive objectives losing their edge under extreme imbalance.
  • I3. External data with a different distribution was pooled to rebalance rare classes, but only as an auxiliary multi-task signal, which limits the harm from distribution mismatch.
  • I4. The task is a cascade of labels, where each finer decision applies only to tweets that passed the coarser one, and the levels are learned jointly.
  • I5. Orthographic variants (Alef forms, digits, punctuation, hashtags split into words) are unified before encoding to shrink sparsity.

For Mova

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

  • I1 (learn): Add negative controls that test whether a trained component leans on artifacts of how the training data was gathered, rather than on structure.
  • I2 (learn): Choose training objectives per component based on measured label skew (e.g., rare dependency relations or rare frame roles) instead of applying one recipe everywhere.
  • I3 (tree): Treebanks in other UD dialects could feed gparse as auxiliary tasks rather than being merged into the main training set, keeping conversion mismatch from contaminating the primary parser.
  • I4 (frames): Speech-act, offence and irony judgments in prag could be organised as nested decisions trained together, so that coarse cues support the sparse fine-grained ones.
  • I5 (tokens): A comparable explicit normalisation layer in crate en (Unicode quotes, digit styles, hashtag or camel-case splitting) would reduce out-of-vocabulary noise for the tagger and lemmatiser.

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 Ahmad Shapiro, Ayman Khalafallah and Marwan Torki. 2022. AlexU-AIC at Arabic Hate Speech 2022: Contrast to Classify. Proceedinsg of the 5th Workshop on Open-Source Arabic Corpora and Processing Tools with Shared Tasks on Qur'an QA and Fine-Grained Hate Speech Detection.

The paper itself, not this page. BibTeX from the library's record of the work.

@inproceedings{shapiro2022alexu,
  title = {{AlexU-AIC at Arabic Hate Speech 2022: Contrast to Classify}},
  author = {Ahmad Shapiro, Ayman Khalafallah and Marwan Torki},
  booktitle = {Proceedinsg of the 5th Workshop on Open-Source Arabic Corpora and Processing Tools with Shared Tasks on Qur'an QA and Fine-Grained Hate Speech Detection},
  year = {2022},
  url = {https://aclanthology.org/2022.osact-1.26/}
}

References

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