Graph machine learning has been extensively studied in both academia and industry. Although booming with a vast number of emerging methods and techniques, most of the literature is built on the I.I.D. hypothesis, i.e., testing and training graph data are independent and identically distributed. However, this I.I.D. hypothesis can hardly be satisfied in many real-world graph scenarios where the model performance substantially degrades when there exist distribution shifts between testing and training graph data. To solve this critical problem, out-of-distribution (OOD) generalization on graphs, which goes beyond the I.I.D. hypothesis, has made great progress and attracted ever-increasing attention from the research community. In this paper, we comprehensively survey OOD generalization on graphs and present a detailed review of recent advances in this area. First, we provide a formal problem definition of OOD generalization on graphs. Second, we categorize existing methods into three classes from conceptually different perspectives, i.e., data, model, and learning strategy, based on their positions in the graph machine learning pipeline, followed by detailed discussions for each category. We also review the theories related to OOD generalization on graphs and introduce the commonly used graph datasets for thorough evaluations. Last but not least, we share our insights on future research directions. This paper is the first systematic and comprehensive review of OOD generalization on graphs, to the best of our knowledge.

我们综合调查了图形领域中的ODD概括率，并详细审查了最近在这个领域取得的进展，然后根据其在图形机器学习流水线中的位置，从数据、模型和学习策略等不同概念上将现有方法分为三类，并对每个类别进行了详细讨论，最后分享了我们对未来研究方向的看法。

图上的外域泛化：一份综述