Towards generalizable Graph Contrastive Learning: An information theory perspective.

Graph Contrastive Learning (GCL) is increasingly employed in graph representation learning with the primary aim of learning node/graph representations from a predefined pretext task that can generalize to various downstream tasks. Meanwhile, the transition from a specific pretext task to diverse and unpredictable downstream tasks poses a significant challenge for GCL's generalization ability. Most existing GCL approaches maximize mutual information between two views derived from the original graph, either randomly or heuristically. However, the generalization ability of GCL and its theoretical principles are still less studied. In this paper, we introduce a novel metric GCL-GE, to quantify the generalization gap between predefined pretext and agnostic downstream tasks. Given the inherent intractability of GCL-GE, we leverage concepts from information theory to derive a mutual information upper bound that is independent of the downstream tasks, thus enabling the metric's optimization despite the variability in downstream tasks. Based on the theoretical insight, we propose InfoAdv, a GCL framework to directly enhance generalization by jointly optimizing GCL-GE and InfoMax. Extensive experiments validate the capability of InfoAdv to enhance performance across a wide variety of downstream tasks, demonstrating its effectiveness in improving the generalizability of GCL.