Cited by 841Natural Language Processing TechniquesAdvanced Neural Network ApplicationsTopic Modeling

The DOI matches its Crossref record; 57 of the 57 references it cites were found in a registry or an index; 4 of the 9 sources its claims cite were checked for support.

Sequence-Level Knowledge Distillation

Open access
Kim, Yoon, Rush, Alexander M.·2016·Proceedings of the 2016 Conference on Empirical Methods in Natural Language Processing

Abstract

Neural machine translation (NMT) offers a novel alternative formulation of translation that is potentially simpler than statistical approaches.However to reach competitive performance, NMT models need to be exceedingly large.In this paper we consider applying knowledge distillation approaches (Bucila et al., 2006;Hinton et al., 2015) that have proven successful for reducing the size of neural models in other domains to the problem of NMT.We demonstrate that standard knowledge distillation applied to word-level prediction can be effective for NMT, and also introduce two novel sequence-level versions of knowledge distillation that further improve performance, and somewhat surprisingly, seem to eliminate the need for beam search (even when applied on the original teacher model).Our best student model runs 10 times faster than its state-of-the-art teacher with little loss in performance.It is also significantly better than a baseline model trained without knowledge distillation: by 4.2/1.7 BLEU with greedy decoding/beam search.Applying weight pruning on top of knowledge distillation results in a student model that has 13× fewer parameters than the original teacher model, with a decrease of 0.4 BLEU.

Overview

AI snapshot

Written from the paper’s full text.

TL;DR

The paper applies knowledge distillation to neural machine translation, showing word-level distillation helps and introducing sequence-level variants (Seq-KD and Seq-Inter) that train a smaller student on teacher beam-search outputs. The best student runs 10× faster than its teacher with little BLEU loss, and pruning on top yields 13× fewer parameters with a 0.4 BLEU drop.

Key findings

  • Word-level knowledge distillation improves over the baseline, but sequence-level knowledge distillation does better on English→German and similarly on Thai→English; combining them gives further gains for the 2×300 and 2×100 models, though not for the 2×500 model. For English→German 2×500, baseline BLEU is 14.7/17.6 (greedy/beam), Seq-KD is 18.9/19.0, and Seq-KD + Seq-Inter is 18.9/19.3, i.e. +4.2/+1.7 BLEU over baseline.
  • Sequence-level distillation reduces the need for beam search: greedy decoding with a fine-tuned teacher (Baseline + Seq-Inter) reaches 19.6 BLEU versus 19.5 for beam search with the original teacher. Seq-KD models also assign much more mass to the approximate mode: 16.9% for the 2×500 English→German Seq-KD model versus 0.9% for the baseline.
  • The student model can run 10× faster with greedy decoding than the teacher with beam search on GPU: 1051.3 vs 101.9 source words/sec.
  • Weight pruning on top of distillation is orthogonal: pruning 80% of weights in the 2×500 Seq-KD + Seq-Inter student gives 13× fewer parameters than the original teacher with only 0.4 BLEU decrease; pruning 90% gives 8m parameters (26× fewer) with a 1.0 BLEU decrease.

Methods

  • Uses an attentional encoder-decoder NMT architecture from Luong et al. (2015). Two settings: English→German WMT 2014 (4m sentences, top 50k vocabulary, teacher 4×1000 LSTM, students 2×300 and 2×500) and Thai→English IWSLT 2015 (90k sentences, 25k vocabulary, teacher 2×500, student 2×100). Evaluation is tokenized BLEU with multi-bleu.perl.
  • Three distillation variants: Word-KD (cross-entropy with teacher word distribution plus NLL; α tested in {0.5, 0.9}, with 0.5 better); Seq-KD (student trained on teacher beam-search output, beam K=5); and Seq-Inter (student trained on the teacher beam hypothesis with highest smoothed sentence BLEU to gold, beam K=35, fine-tuned from a pretrained model with learning rate 0.1; English→German Seq-Inter data generated on ~50% of the training set). Methods can be combined.
  • Weight pruning removes weights with lowest absolute values, then retrains on Seq-KD data with learning rate 0.2 and fine-tunes toward Seq-Inter data with learning rate 0.1. Speed is measured on GPU (GeForce GTX Titan X), CPU, and smartphone (Samsung Galaxy 6).

Limitations

  • Stated: the mode approximation for sequence-level distillation is poor because it approximates an exponentially sized distribution with a single sample; Seq-Inter’s two-sequence interpolation is nonideal because it doubles training data and requires training on both teacher-generated and true sequences conditioned on the same source, which are often different. The paper also calls its illustrative noise function “simple (unrealistic).”
  • Stated: experiments cover only English→German and Thai→English NMT; the 4×1000 model could not be opened on the smartphone; larger beam sizes than K=5 did not improve results; and English→German Seq-Inter data was generated on only ~50% of the training set for efficiency.
  • Evident from the text: no statistical significance tests are reported, hyperparameter searches are narrow (τ ∈ {1, 1.5, 2}; α ∈ {0.5, 0.9}), and compression is compared mainly against pruning rather than other compression families.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.18653/v1/d16-1139

Cites

57 of 57 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Verification

Claims the paper makes

26 Own result · 13 Own interpretation · 9 No basis given · 3 Sources not found · 2 Partly supported · 1 Supported · 1 Supported so far · accuracy not yet measured

Show all 35 claims

  • It may state two separate claims as one. 15
  • Probably not a substantial claim. 6
20 of 20
  • The authors state this as an assumption.

    The teacher has previously been trained, and we are estimating parameters for the student.

    “We generally assume that the teacher has previously been trained, and that we are estimating parameters for the student.”
  • The authors state this as an assumption.

    The teacher distribution parameters remain fixed during student training.

    “where θ T parameterizes the teacher distribution and remains fixed.”
  • The paper relies on this without support.

    Run-time complexity for beam search grows linearly with beam size.

    “Run-time complexity for beam search grows linearly with beam size.”
  • The paper relies on this without support.

    Combining pruning and knowledge distillation has not been investigated before.

    “To our knowledge combining pruning and knowledge distillation has not been investigated before.”
  • The paper relies on this without support.

    The translation domain has generally required the largest capacity deep learning models.

    “We have chosen to focus on translation as this domain has generally required the largest capacity deep learning models”
5 of 5

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Citations

Cites

Show all 53 references

Research works printed but not linked: 4

  1. Cristian Bucila, Rich Caruana, and Alexandru Niculescu-Mizil. 2006. Model Compres- sion. In Proceedings of KDD.
  2. and Blunsom2013] Nal Kalchbrenner and Phil Blunsom. 2013. Recurrent Continuous Transla- tion Models. In Proceedings of EMNLP.
  3. Jiwei Li, Michael Galley, Chris Brockett, Jianfeg Gao, and Bill Dolan. 2016. A Diversity- Promoting Objective Function for Neural Conversa- tional Models. In Proceedings of NAACL 2016.
  4. Mariet and Sra2016] Zelda Mariet and Suvrit Sra. 2016. Diversity Networks. In Proceedings of ICLR.

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Metadata

Authors
Kim, Y., & Rush, A. M.
Affiliations
Harvard University (US)
Venue
Proceedings of the 2016 Conference on Empirical Methods in Natural Language Processing
Published
2016
Pages
1317-1327
OpenAlex
W2963736842
Cited by
836
References
53
Citations by year
2026: 36 · 2025: 59 · 2024: 52 · 2023: 137 · 2022: 115 · 2021: 157 · 2020: 143 · 2019: 75 · 2018: 42 · 2017: 16 · 2016: 4
FWCI
24.59
Type
conference paper
Language
en
Open access
Licence
cc-by
Locations
  • Conference on Empirical Methods in Natural Language Processing (EMNLP) (publishedVersion, cc-by)
  • arXiv (Cornell University) (submittedVersion)
  • arXiv (Cornell University)
Topics
  • Physical Sciences › Computer Science › Artificial Intelligence › Natural Language Processing Techniques
  • Physical Sciences › Computer Science › Computer Vision and Pattern Recognition › Advanced Neural Network Applications
  • Physical Sciences › Computer Science › Artificial Intelligence › Topic Modeling
Keywords
knowledge distillation, neural machine translation, model compression, weight pruning, teacher-student models, parameter reduction

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