The class imbalance problem, as an important issue in learning node
representations, has drawn increasing attention from the community. Although
the imbalance considered by existing studies roots from the unequal quantity of
labeled examples in different classes (quantity imbalance), we argue that graph
data expose a unique source of imbalance from the asymmetric topological
properties of the labeled nodes, i.e., labeled nodes are not equal in terms of
their structural role in the graph (topology imbalance). In this work, we first
probe the previously unknown topology-imbalance issue, including its
characteristics, causes, and threats to semi-supervised node classification
learning. We then provide a unified view to jointly analyzing the quantity- and
topology- imbalance issues by considering the node influence shift phenomenon
with the Label Propagation algorithm. In light of our analysis, we devise an
influence conflict detection -- based metric Totoro to measure the degree of
graph topology imbalance and propose a model-agnostic method ReNode to address
the topology-imbalance issue by re-weighting the influence of labeled nodes
adaptively based on their relative positions to class boundaries. Systematic
experiments demonstrate the effectiveness and generalizability of our method in
relieving topology-imbalance issue and promoting semi-supervised node
classification. The further analysis unveils varied sensitivity of different
graph neural networks (GNNs) to topology imbalance, which may serve as a new
perspective in evaluating GNN architectures.

本论文主要探讨了在学习节点表示过程中，类不平衡问题是如何影响图像的，同时提出了一种识别和解决图拓扑不平衡问题的新方法，并在系统实验中证明了该方法在缓解拓扑不平衡问题和促进半监督节点分类中的有效性和通用性，同时揭示了不同 GNN 架构对拓扑不平衡的敏感性。