Towards Mechanistic Interpretability of Graph Transformers via Attention Graphs
This provides a tool for mechanistic interpretability in graph learning, which is incremental as it builds on existing methods for analyzing attention in Transformers.
The paper tackled the problem of interpreting Graph Transformers by introducing Attention Graphs to analyze information flow, finding that learned attention patterns do not correlate with input graph structures and that different variants achieve similar performance with distinct patterns on heterophilous graphs.
We introduce Attention Graphs, a new tool for mechanistic interpretability of Graph Neural Networks (GNNs) and Graph Transformers based on the mathematical equivalence between message passing in GNNs and the self-attention mechanism in Transformers. Attention Graphs aggregate attention matrices across Transformer layers and heads to describe how information flows among input nodes. Through experiments on homophilous and heterophilous node classification tasks, we analyze Attention Graphs from a network science perspective and find that: (1) When Graph Transformers are allowed to learn the optimal graph structure using all-to-all attention among input nodes, the Attention Graphs learned by the model do not tend to correlate with the input/original graph structure; and (2) For heterophilous graphs, different Graph Transformer variants can achieve similar performance while utilising distinct information flow patterns. Open source code: https://github.com/batu-el/understanding-inductive-biases-of-gnns