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Rethinking the Power of Graph Canonization in Graph Representation Learning with Stability
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Proposes graph-canonization-enhanced GNNs (GC-GNN) that use canonical node orderings as positional encodings, identifies an expressivity-stability trade-off, and introduces universal graph canonization (UGC-GNN) with a sufficient condition based on dataset-wide node labeling.
Problem
GNNs are limited by 1-WL expressivity; graph canonization can distinguish non-isomorphic graphs, but canonical node labelings are unstable under small graph perturbations, hurting generalization to unseen graphs.
Approach
Use graph canonization outputs as one-hot node positional encodings to maximize expressivity, then resolve the resulting stability loss with a dataset-level "universal" canonization defined via a globally injective node labeling l(v|G) that is consistent across graphs, also applied in the readout layer via per-label weight matrices.
Key results
- GC-GNN (GIN) reaches 1.00 train and 0.9667 test accuracy on CSL versus 0.1400/0.1157 for GIN; on TU datasets GC-GNN improves backbones by up to 29.6% on D&D, and GC-GNN (GraphSAGE) reaches 89.4% on MUTAG.
- UGC-GNN (GIN) achieves 0.624 accuracy on Mayo, 0.701 on RosMap and 0.714 on Cancer Subtype, outperforming listed gene-network DL baselines such as MLA-GNN (0.589, 0.595, 0.631).
- On NA and BN DAG regression, UGC-GNN (GIN) obtains RMSE 0.253 and 0.120, improving over SAN (0.311 and 0.158).
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| add graph canonization positional encodings to GIN/GCN | GIN, GCN · EXP and CSL isomorphism tests | test accuracy: EXP GCN 0.5000 -> 0.9267; GIN 0.5000 -> 0.9975 | Helped |
| add graph canonization (GC-GNN) to backbone GNNs | TU datasets (GCN, GraphSAGE, GIN, GAT) · D&D, MUTAG, PROTEINS, PTC-MR, ENZYMES | accuracy: average improvement over backbone 6.0% to 28.2% across datasets; max 29.6% on D&D | Helped |
| add graph canonization to GNN backbones | TU datasets · ENZYMES and PTC-MR (some GC-GNN variants) | accuracy: GC-GNN (GIN) 30.7 on ENZYMES and 57.2 on PTC-MR, below several baselines such as GIN-AK+ and SignNet | Mixed |
| add general graph canonization (GC) to GIN on gene networks | GIN on Mayo, RosMap, Cancer · gene network datasets | accuracy: Mayo GIN 0.496 -> GC-GNN 0.483; RosMap GIN 0.471 -> GC-GNN 0.486 (Mayo worse) | Hurt |
| replace general graph canonization with universal graph canonization (UGC) on GIN (ablation) | GIN on gene networks and brain graphs · Mayo, RosMap, Cancer, fMRI-ABIDE | accuracy: Mayo 0.483 (GC) -> 0.624 (UGC); RosMap 0.486 -> 0.701; Cancer 0.539 -> 0.714; fMRI-ABIDE 0.610 -> 0.648 | Helped |
| add universal graph canonization (UGC) to GIN | GIN on DAG datasets · NA and BN | RMSE (lower better): NA 0.264 (DAGNN best baseline) -> 0.253; BN 0.122 -> 0.120 | Helped |
| add universal graph canonization to GIN | GIN on gene networks · Mayo, RosMap, Cancer | accuracy: Mayo 0.496 -> 0.624 (GIN backbone to UGC-GNN); RosMap 0.471 -> 0.701 | Helped |
| add general graph canonization (GC) to GCN on gene networks (ablation) | GCN · Mayo, RosMap, Cancer Subtype | accuracy: Mayo GCN 0.561 -> 0.522; RosMap 0.520 -> 0.508; Cancer 0.593 -> 0.544 | Mixed |
| add universal graph canonization (UGC) to GCN (ablation) | GCN · Mayo, RosMap, Cancer Subtype | accuracy: Mayo 0.561 -> 0.572 (UGC); RosMap 0.520 -> 0.658; Cancer 0.593 -> 0.619 | Mixed |
| add graph canonization to GIN on molecular datasets (ablation) | GIN · ogbg-molhiv and ogbg-molpcba | AUC / AP: molhiv GIN 0.7744 -> GN-GIN 0.7705 (drop); molpcba 0.2703 -> 0.2781 (gain) | Mixed |
Surprising findings
- General graph canonization (GC-GNN) often performs worse than the GIN backbone on large gene networks (Mayo, RosMap, Cancer), supporting the claimed stability trade-off.
- GC-GNN (GIN) gets lower than GIN on ogbg-molhiv-type settings and does not reach SOTA on OGB molecular datasets.
Limitations
- Universal graph canonization requires a dataset-level injective node labeling, which is only available in specific domains (gene networks, brain graphs, grids, DAGs).
- Graph canonization ignores edge heterogeneity and is not suited to all tasks; gains on OGB molecular datasets are modest and not SOTA.
- Stability/generalization results are theoretical with loose constants and empirical comparison is limited to a subset of baselines.
Experimental setup
Datasets: EXP CSL TU datasets (PROTEINS, PTC-MR, MUTAG, ENZYMES, D&D) Mayo RosMap Cancer Subtype fMRI ABIDE NA (ENAS neural architectures) BN (bnlearn Bayesian networks) ogbg-molhiv ogbg-molpcba
Benchmarks: EXP CSL TU datasets Mayo RosMap Cancer Subtype fMRI ABIDE NA BN ogbg-molhiv ogbg-molpcba
Metrics: accuracy F1 score RMSE Pearson's r ROC-AUC AP
Baselines: GCN GIN GAT GraphSAGE Nested GNN GraphSNN GIN-AK+ SignNet ESAN DropGNN GNN-RNI PPGN
Builds on: Weisfeiler-Lehman test Nauty Graph Isomorphism Network Nested GNN positional encoding for graph transformers
Closest papers by meaning
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