  Self-supervised learning on graphs can be bifurcated into contrastive and
generative methods. Contrastive methods, also known as graph contrastive
learning (GCL), have dominated graph self-supervised learning in the past few
years, but the recent advent of graph masked autoencoder (GraphMAE) rekindles
the momentum behind generative methods. Despite the empirical success of
GraphMAE, there is still a dearth of theoretical understanding regarding its
efficacy. Moreover, while both generative and contrastive methods have been
shown to be effective, their connections and differences have yet to be
thoroughly investigated. Therefore, we theoretically build a bridge between
GraphMAE and GCL, and prove that the node-level reconstruction objective in
GraphMAE implicitly performs context-level GCL. Based on our theoretical
analysis, we further identify the limitations of the GraphMAE from the
perspectives of alignment and uniformity, which have been considered as two key
properties of high-quality representations in GCL. We point out that GraphMAE's
alignment performance is restricted by the masking strategy, and the uniformity
is not strictly guaranteed. To remedy the aforementioned limitations, we
propose an Alignment-Uniformity enhanced Graph Masked AutoEncoder, named
AUG-MAE. Specifically, we propose an easy-to-hard adversarial masking strategy
to provide hard-to-align samples, which improves the alignment performance.
Meanwhile, we introduce an explicit uniformity regularizer to ensure the
uniformity of the learned representations. Experimental results on benchmark
datasets demonstrate the superiority of our model over existing
state-of-the-art methods.
