Fast and Accurate Entity Recognition with Iterated Dilated Convolutions
Summary
Bi-LSTM encoders, often paired with a CRF, are the standard approach to sequence tagging, but they process tokens one after another and cannot fully use GPU parallelism. Strubell et al. propose Iterated Dilated CNNs (ID-CNNs) as a faster token encoder for English NER. Dilated convolutions skip over inputs at a growing rate, so the context each token sees expands exponentially with depth without reducing output resolution. To avoid the overfitting that comes from simply stacking more layers, the model reuses one small dilated block several times with shared weights. It is trained so that the output after every iteration should already give correct labels. The authors evaluate on CoNLL 2003 and OntoNotes 5.0 English NER, using both independent per-token prediction and CRF/Viterbi decoding. ID-CNNs reach accuracy close to a Bi-LSTM-CRF while running 14–20× faster at test time. When applied to whole documents, they match or exceed it and are still almost 8× faster. This matters for large-scale tagging, where both compute time and energy use are real costs.
Key points
- Effective input width (receptive field) grows exponentially with depth. Four dilated layers of width 3 already cover 31 tokens, more than the 23-token average sentence in the Penn TreeBank. With radius 2 and 8 layers, coverage exceeds 1,000 tokens, which is enough for a full newswire document.
- On document-level CoNLL 2003, the greedy ID-CNN scores 90.65 F1, compared with 90.60 for the Bi-LSTM-CRF and 89.09 for the Bi-LSTM. It decodes 7.96× faster than the Bi-LSTM-CRF, while the greedy Bi-LSTM is only 4.60× faster.
- Ablations on CoNLL show that both design choices help:
- untying block parameters drops F1 to 89.81;
- applying the loss only at the final layer drops F1 to 90.06.
- On OntoNotes 5.0, the authors' Bi-LSTM-CRF reaches 86.99 F1, ID-CNN-CRF reaches 86.84, and the greedy ID-CNN with 3 blocks reaches 85.27. The greedy ID-CNN still beats the Bi-LSTM (83.76) and Durrett and Klein (2014).
- Adding document context helps the ID-CNN on OntoNotes (85.76). It slightly hurts the Bi-LSTM-CRF (86.81). The implementation is in TensorFlow at github.com/iesl/dilated-cnn-ner.
Interesting ideas
- I1. Weight tying across repeated blocks. Applying one shared dilated block several times, instead of building a deeper network, gives wide context without adding parameters or overfitting. This could suit small-data settings, such as low-resource Ukrainian corpora, where deep models overfit easily.
- I2. Supervision after every iteration. Each pass is pushed to produce good labels, and later passes can then fix inconsistencies left by earlier ones. This acts as a cheap form of iterative refinement and could be added to other stacked or recurrent encoders.
- I3. Doubling the dilation rate. Starting with dilation 1 and doubling it at each layer gives full coverage of the input with no gaps, and the parameter count grows only linearly. The same layout could serve any long-sequence task where per-position output must keep full resolution.
- I4. Document-level context at low cost. Because the runtime of the convolutions does not depend on sequence length, feeding whole documents becomes practical. The paper also shows that the gain varies by dataset: it is larger on CoNLL, which has many ambiguous entities. This is a useful reminder to check, per corpus, whether extra context actually helps.
- I5. Deciding between greedy and CRF decoding. The paper finds that the greedy-vs-Viterbi gap widens when entities are longer and more varied, as in OntoNotes. Looking at entity length statistics before choosing a decoder could save compute when structured decoding is unlikely to add much.
Cited by
- New Insights into Cross-Document Event Coreference: Systematic Comparison and a Simplified Approach
- Template-Based Named Entity Recognition Using BART
- Modeling Speech Acts in Asynchronous Conversations: A Neural-CRF Approach
- A Neural Layered Model for Nested Named Entity Recognition
- A Unified MRC Framework for Named Entity Recognition
- Towards JointUD: Part-of-speech Tagging and Lemmatization using Recurrent Neural Networks
- Double Embeddings and CNN-based Sequence Labeling for Aspect Extraction
- Named Entity Recognition as Dependency Parsing
Cite
@inproceedings{strubell2017fast,
title = {{Fast and Accurate Entity Recognition with Iterated Dilated Convolutions}},
author = {Strubell, Emma and Verga, Patrick and Belanger, David and McCallum, Andrew},
booktitle = {Proceedings of the 2017 Conference on Empirical Methods in Natural Language Processing},
year = {2017},
doi = {10.18653/v1/d17-1283},
url = {https://doi.org/10.18653/v1/d17-1283}
}References
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