Attention Is All You Need¶
A Revolutionary Architecture for Sequence Transduction¶
Ashish Vaswani et al.
NIPS 2017
Abstract¶
- First sequence transduction model based solely on attention
- Dispenses with recurrence and convolutions entirely
- More parallelizable and faster to train than traditional models
- New state-of-the-art: 28.4 BLEU (EN-DE) and 41.8 BLEU (EN-FR)
- Generalizes well to English constituency parsing
Background: Limitations of Traditional Models¶
Recurrent Models (RNN/LSTM/GRU)¶
- Inherently sequential computation → limited parallelization
- O(n) sequential operations for long-range dependencies
Convolutional Models¶
- Fixed kernel size restricts context → requires multiple layers
- Logarithmic path length for distant connections
Key Innovation: Self-Attention Mechanism¶
- Connects all positions with constant operations
- Enables parallel computation across sequence
- Directly models long-range dependencies
- More efficient than RNN/CNN for typical sequence lengths
Transformer Model Architecture¶
Encoder-decoder structure with stacked self-attention and feed-forward layers.
Encoder Architecture¶
- Stack of 6 identical layers
- Each layer has two sub-layers:
- Multi-head self-attention mechanism
- Position-wise feed-forward network
- Residual connections + layer normalization
- Output dimension: dmodel = 512
Decoder Architecture¶
- Stack of 6 identical layers
- Three sub-layers per layer:
- Masked multi-head self-attention (prevents future positions)
- Encoder-decoder attention (queries from decoder, keys/values from encoder)
- Position-wise feed-forward network
- Residual connections + layer normalization
Attention Mechanisms¶
Scaled Dot-Product Attention¶
$\(\text{Attention}(Q, K, V) = \text{softmax}\left(\frac{QK^T}{\sqrt{d_k}}\right)V\)$ - Scaling avoids gradient vanishing for large dk
Multi-Head Attention¶
$\(\text{MultiHead}(Q, K, V) = \text{Concat}(\text{head}_1,...,\text{head}_h)W^O\)$ - h=8 parallel heads, dk=dv=64 → captures diverse patterns
Positional Encoding¶
- Injects sequence order information (no recurrence/convolution)
- Added to input embeddings (same dmodel dimension)
- Uses sine/cosine functions with varying frequencies: $\(PE_{(pos,2i)} = \sin(pos/10000^{2i/d_{\text{model}}})\)$ $\(PE_{(pos,2i+1)} = \cos(pos/10000^{2i/d_{\text{model}}})\)$
- Enables learning of relative position relationships
Why Self-Attention?¶
| Aspect | Self-Attention | Recurrent | Convolutional |
|---|---|---|---|
| Complexity | O(n²·d) | O(n·d²) | O(k·n·d²) |
| Parallelization | O(1) | O(n) | O(1) |
| Long-range path length | O(1) | O(n) | O(logk(n)) |
- Superior parallelization and dependency modeling
Training Setup¶
Data & Hardware¶
- WMT 2014 EN-DE (4.5M) and EN-FR (36M) sentence pairs
- 8 NVIDIA P100 GPUs, 12h (base)/3.5d (big model) training
Optimization¶
- Adam (β1=0.9, β2=0.98, ϵ=10⁻⁹) with linear warmup (4000 steps) + inverse square root decay
- Regularization: residual dropout (0.1), label smoothing (0.1)
Machine Translation Results¶
| Model | EN-DE BLEU | EN-FR BLEU | Training Cost (FLOPs) |
|---|---|---|---|
| GNMT + RL Ensemble | 26.30 | 41.16 | 1.8×10²⁰ / 1.1×10²¹ |
| ConvS2S Ensemble | 26.36 | 41.29 | 7.7×10¹⁹ / 1.2×10²¹ |
| Transformer (big) | 28.4 | 41.8 | 2.3×10¹⁹ |
- New state-of-the-art with 4× lower training cost
Model Ablations & Generalization¶
Key Ablations (EN-DE Dev Set)¶
| Variation | Dev BLEU | Insight |
|---|---|---|
| Single head | 24.9 | Multi-head critical |
| No dropout | 25.3 | Regularization needed |
| Learned pos encoding | 25.7 | Sinusoidal ≈ learned |
Constituency Parsing¶
- 91.3 F1 (WSJ only) vs. 91.7 (state-of-the-art)
- 92.7 F1 (semi-supervised) → strong generalization
Attention Visualization: Long-Distance Dependencies¶
Encoder self-attention (layer 5) tracking "making...more difficult" dependency.
Attention Visualization: Anaphora Resolution¶
Attention heads resolving "its" to referent "The Law".
Limitations & Future Work¶
Limitations¶
- Quadratic complexity in sequence length
- Less efficient for very long sequences
- Still sequential in generation
Future Work¶
- Local/restricted attention mechanisms
- Extension to other modalities (images, audio)
- Non-sequential generation approaches
Conclusion¶
- Transformer replaces recurrence/convolution with self-attention
- Sets new state-of-the-art in machine translation
- Faster training via parallelization
- Generalizes well to diverse sequence tasks
- Foundation for modern attention-based NLP models