I. Introduction
Graphs are ubiquitous data structures that model the pairwise interactions between entities [1]. With the remarkable success of deep learning, Graph neural networks (GNNs) leverage artificial neural networks for graph representation learning. GNNs recursively aggregate the features of nodes and edges to obtain intrinsic and essential graph information, which achieves high performance in graph-related tasks such as node and graph classification [2], link prediction [3], molecular graph generation [4] and knowledge graph completion [5].