Scheduled Multi-Task Learning: From Syntax to Translation
Written for the Research library (claude-opus-5-5) from the paper text. Original — aclanthology.org/Q18-1017.pdf
Summary
Neural machine translation systems learn source and target language structure only implicitly, which can lead to overly strong linguistic generalizations. Kiperwasser and Ballesteros add explicit syntactic supervision through a single shared attentional sequence-to-sequence model. A task token placed at the start of the decoder output tells the model which task to perform. Part-of-speech tagging, unlabeled dependency parsing (written as each word's signed distance to its head) and dependency labeling are all cast as sequence outputs alongside translation.
The central idea is Scheduled Multi-Task Learning. A scheduler randomly picks which task's queue supplies the next training example, and the auxiliary syntactic tasks gradually lose weight. This setup blends pre-training, multi-task learning and fine-tuning. Experiments on WMT14 English→German and low-resource WIT/IWSLT German→English report BLEU gains, with results strongly dependent on the scheduler chosen. The trained models can still perform tagging and parsing. The work matters because it offers a simple, architecture-agnostic way to inject syntax into NMT, especially when parallel data is scarce.
Key points
- Unlabeled trees are encoded as sequences of head distances, e.g. "2 1 1 -4 -1 1 -2". Unlike absolute head positions, this representation generalizes to sentence lengths rarely seen in training.
- The exponential scheduler gave the best average results on WIT German→English. It starts close to auxiliary-task pre-training and progressively shifts focus to translation.
- On WMT14 English→German, the sigmoid scheduler (multi-task first, then fine-tuning) was the strongest scheduler on average. However, it still did not beat the baseline without multi-task learning.
- On IWSLT, the average of four runs without SMTL was 28.5 BLEU. With SMTL, the best scores peaked at 29.68 BLEU for separate decoders with a shared encoder and 29.55 BLEU for the shared decoder.
- Separate decoders were more sensitive to the scheduler slope α than the shared decoder (σ = 0.38 vs 0.21). Parsing and tagging accuracies remained modest.
Cited by
- Hexatagging: Projective Dependency Parsing as Tagging
- Few-Shot and Zero-Shot Learning for Historical Text Normalization
- Massively Multilingual Neural Machine Translation in the Wild: Findings and Challenges
Cite
@article{kiperwasser2018scheduled,
title = {{Scheduled Multi-Task Learning: From Syntax to Translation}},
author = {Kiperwasser, Eliyahu and Ballesteros, Miguel},
journal = {Transactions of the Association for Computational Linguistics},
year = {2018},
doi = {10.1162/tacl\_a\_00017},
url = {https://doi.org/10.1162/tacl_a_00017}
}References
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