Eliciting Structural and Semantic Global Knowledge in Unsupervised Graph Contrastive Learning

Graph Contrastive Learning (GCL) has recently drawn much research interest for learning generalizable node representations in a self-supervised manner. In general, the contrastive learning process in GCL is performed on top of the representations learned by a graph neural network (GNN) backbone, which transforms and propagates the node contextual information based on its local neighborhoods. However, nodes sharing similar characteristics may not always be closely connected, which poses a great challenge for unsupervised GCL efforts due to their inherent limitations in capturing such global graph knowledge. In this work, we address their inherent limitations by proposing a simple yet effective framework - Simple Neural Networks with Structural and Semantic Contrastive Learning (S3-CL). Notably, by virtue of the proposed structural and semantic contrastive learning algorithms, even a simple neural network can learn expressive node representations that preserve valuable global structural and semantic patterns. Our experiments demonstrate that the node representations learned by S3-CL achieve superior performance on different down-stream tasks compared with the state-of-the-art unsupervised GCL methods. Implementation and more experimental details are publicly available at https://github.com/kaize0409/S-3-CL.