基于图形神经网络（GNN）的子图表学习在科学进步中表现出广泛的应用，例如对分子结构 - 特质关系和集体细胞功能的预测。特别是，图表增强技术在改善基于图和基于节点的分类任务方面显示出令人鼓舞的结果。尽管如此，在现有的基于GNN的子图表示学习研究中很少探索它们。在这项研究中，我们开发了一种新型的多视图增强机制，以改善子图表示学习模型，从而改善下游预测任务的准确性。我们的增强技术创建了多种子图的变体，并将这些变体嵌入原始图中，以实现高度改善的训练效率，可伸缩性和准确性。几个现实世界和生理数据集的基准实验证明了我们提出的多视图增强技术在子图表学习中的优越性。

Data-efficient learning on graphs (GEL) is essential in real-world applications. Existing GEL methods focus on learning useful representations for nodes, edges, or entire graphs with ``small'' labeled data. But the problem of data-efficient learning for subgraph prediction has not been explored. The challenges of this problem lie in the following aspects: 1) It is crucial for subgraphs to learn positional features to acquire structural information in the base graph in which they exist. Although the existing subgraph neural network method is capable of learning disentangled position encodings, the overall computational complexity is very high. 2) Prevailing graph augmentation methods for GEL, including rule-based, sample-based, adaptive, and automated methods, are not suitable for augmenting subgraphs because a subgraph contains fewer nodes but richer information such as position, neighbor, and structure. Subgraph augmentation is more susceptible to undesirable perturbations. 3) Only a small number of nodes in the base graph are contained in subgraphs, which leads to a potential ``bias'' problem that the subgraph representation learning is dominated by these ``hot'' nodes. By contrast, the remaining nodes fail to be fully learned, which reduces the generalization ability of subgraph representation learning. In this paper, we aim to address the challenges above and propose a Position-Aware Data-Efficient Learning framework for subgraph neural networks called PADEL. Specifically, we propose a novel node position encoding method that is anchor-free, and design a new generative subgraph augmentation method based on a diffused variational subgraph autoencoder, and we propose exploratory and exploitable views for subgraph contrastive learning. Extensive experiment results on three real-world datasets show the superiority of our proposed method over state-of-the-art baselines.

生物医学网络是与疾病网络的蛋白质相互作用的普遍描述符，从蛋白质相互作用，一直到医疗保健系统和科学知识。随着代表学习提供强大的预测和洞察的显着成功，我们目睹了表现形式学习技术的快速扩展，进入了这些网络的建模，分析和学习。在这篇综述中，我们提出了一个观察到生物学和医学中的网络长期原则 - 而在机器学习研究中经常出口 - 可以为代表学习提供概念基础，解释其当前的成功和限制，并告知未来进步。我们综合了一系列算法方法，即在其核心利用图形拓扑到将网络嵌入到紧凑的向量空间中，并捕获表示陈述学习证明有用的方式的广度。深远的影响包括鉴定复杂性状的变异性，单细胞的异心行为及其对健康的影响，协助患者的诊断和治疗以及制定安全有效的药物。

对比学习在图表学习领域表现出了巨大的希望。通过手动构建正/负样本，大多数图对比度学习方法依赖于基于矢量内部产品的相似性度量标准来区分图形表示样品。但是，手工制作的样品构建（例如，图表的节点或边缘的扰动）可能无法有效捕获图形的固有局部结构。同样，基于矢量内部产品的相似性度量标准无法完全利用图形的局部结构来表征图差。为此，在本文中，我们提出了一种基于自适应子图生成的新型对比度学习框架，以实现有效且强大的自我监督图表示学习，并且最佳传输距离被用作子绘图之间的相似性度量。它的目的是通过捕获图的固有结构来生成对比样品，并根据子图的特征和结构同时区分样品。具体而言，对于每个中心节点，通过自适应学习关系权重与相应邻域的节点，我们首先开发一个网络来生成插值子图。然后，我们分别构建来自相同和不同节点的子图的正和负对。最后，我们采用两种类型的最佳运输距离（即Wasserstein距离和Gromov-Wasserstein距离）来构建结构化的对比损失。基准数据集上的广泛节点分类实验验证了我们的图形对比学习方法的有效性。

Recently, graph neural networks (GNNs) have revolutionized the field of graph representation learning through effectively learned node embeddings, and achieved state-of-the-art results in tasks such as node classification and link prediction. However, current GNN methods are inherently flat and do not learn hierarchical representations of graphs-a limitation that is especially problematic for the task of graph classification, where the goal is to predict the label associated with an entire graph. Here we propose DIFFPOOL, a differentiable graph pooling module that can generate hierarchical representations of graphs and can be combined with various graph neural network architectures in an end-to-end fashion. DIFFPOOL learns a differentiable soft cluster assignment for nodes at each layer of a deep GNN, mapping nodes to a set of clusters, which then form the coarsened input for the next GNN layer. Our experimental results show that combining existing GNN methods with DIFFPOOL yields an average improvement of 5-10% accuracy on graph classification benchmarks, compared to all existing pooling approaches, achieving a new state-of-the-art on four out of five benchmark data sets.

子图是图中丰富的子结构，并且可以在现实世界任务中部分观察到它们的节点和边缘。在部分观察结果下，现有的节点或子图级消息传播会产生次优表示。在本文中，我们制定了一项新的学习表征的新任务。为了解决此问题，我们建议将部分子图信息（PSI）框架（PSI）框架概括为我们的框架中现有的Infomax模型，包括DGI，Intograph，MVGRL和GraphCl。这些模型最大程度地提高了部分子图的摘要与从节点到完整子图的各种子结构之间的共同信息。此外，我们建议使用$ K $ -HOP PSI的新型两阶段模型，它重建了完整子图的表示，并提高了其从不同局部全球结构中的表现力。在为此问题设计的培训和评估协议下，我们在三个现实世界数据集上进行实验，并证明PSI模型的表现优于基准。

由于其独立性与标签及其稳健性的独立性，自我监督的学习最近引起了很多关注。目前关于本主题的研究主要使用诸如图形结构的静态信息，但不能很好地捕获诸如边缘时间戳的动态信息。现实图形通常是动态的，这意味着节点之间的交互发生在特定时间。本文提出了一种自我监督的动态图形表示学习框架（DYSUBC），其定义了一个时间子图对比学学习任务，以同时学习动态图的结构和进化特征。具体地，首先提出了一种新的时间子图采样策略，其将动态图的每个节点作为中心节点提出，并使用邻域结构和边缘时间戳来采样相应的时间子图。然后根据在编码每个子图中的节点之后，根据中心节点上的邻域节点的影响设计子图表示功能。最后，定义了结构和时间对比损失，以最大化节点表示和时间子图表示之间的互信息。五个现实数据集的实验表明（1）DySubc比下游链路预测任务中的两个图形对比学习模型和四个动态图形表示学习模型更好地表现出更好的相关基线，（2）使用时间信息不能使用只有更有效的子图，还可以通过时间对比损失来学习更好的表示。

图表表示学习（GRL）对于图形结构数据分析至关重要。然而，大多数现有的图形神经网络（GNNS）严重依赖于标签信息，这通常是在现实世界中获得的昂贵。现有无监督的GRL方法遭受某些限制，例如对单调对比和可扩展性有限的沉重依赖。为了克服上述问题，鉴于最近的图表对比学习的进步，我们通过曲线图介绍了一种新颖的自我监控图形表示学习算法，即通过利用所提出的调整变焦方案来学习节点表示来学习节点表示。具体地，该机制使G-Zoom能够从多个尺度的图表中探索和提取自我监督信号：MICRO（即，节点级别），MESO（即，邻域级）和宏（即，子图级） 。首先，我们通过两个不同的图形增强生成输入图的两个增强视图。然后，我们逐渐地从节点，邻近逐渐为上述三个尺度建立三种不同的对比度，在那里我们最大限度地提高了横跨尺度的图形表示之间的协议。虽然我们可以从微距和宏观视角上从给定图中提取有价值的线索，但是邻域级对比度基于我们的调整后的缩放方案提供了可自定义选项的能力，以便手动选择位于微观和介于微观之间的最佳视点宏观透视更好地理解图数据。此外，为了使我们的模型可扩展到大图，我们采用了并行图形扩散方法来从图形尺寸下解耦模型训练。我们对现实世界数据集进行了广泛的实验，结果表明，我们所提出的模型始终始终优于最先进的方法。

对比度学习是图表学习中的有效无监督方法，对比度学习的关键组成部分在于构建正和负样本。以前的方法通常利用图中节点的接近度作为原理。最近，基于数据增强的对比度学习方法已进步以显示视觉域中的强大力量，一些作品将此方法从图像扩展到图形。但是，与图像上的数据扩展不同，图上的数据扩展远不那么直观，而且很难提供高质量的对比样品，这为改进留出了很大的空间。在这项工作中，通过引入一个对抗性图视图以进行数据增强，我们提出了一种简单但有效的方法，对抗图对比度学习（ARIEL），以在合理的约束中提取信息性的对比样本。我们开发了一种称为稳定训练的信息正则化的新技术，并使用子图抽样以进行可伸缩。我们通过将每个图形实例视为超级节点，从节点级对比度学习到图级。 Ariel始终优于在现实世界数据集上的节点级别和图形级分类任务的当前图对比度学习方法。我们进一步证明，面对对抗性攻击，Ariel更加强大。

Graph neural networks (GNNs) have received remarkable success in link prediction (GNNLP) tasks. Existing efforts first predefine the subgraph for the whole dataset and then apply GNNs to encode edge representations by leveraging the neighborhood structure induced by the fixed subgraph. The prominence of GNNLP methods significantly relies on the adhoc subgraph. Since node connectivity in real-world graphs is complex, one shared subgraph is limited for all edges. Thus, the choices of subgraphs should be personalized to different edges. However, performing personalized subgraph selection is nontrivial since the potential selection space grows exponentially to the scale of edges. Besides, the inference edges are not available during training in link prediction scenarios, so the selection process needs to be inductive. To bridge the gap, we introduce a Personalized Subgraph Selector (PS2) as a plug-and-play framework to automatically, personally, and inductively identify optimal subgraphs for different edges when performing GNNLP. PS2 is instantiated as a bi-level optimization problem that can be efficiently solved differently. Coupling GNNLP models with PS2, we suggest a brand-new angle towards GNNLP training: by first identifying the optimal subgraphs for edges; and then focusing on training the inference model by using the sampled subgraphs. Comprehensive experiments endorse the effectiveness of our proposed method across various GNNLP backbones (GCN, GraphSage, NGCF, LightGCN, and SEAL) and diverse benchmarks (Planetoid, OGB, and Recommendation datasets). Our code is publicly available at \url{https://github.com/qiaoyu-tan/PS2}

Graph anomaly detection (GAD) is a vital task in graph-based machine learning and has been widely applied in many real-world applications. The primary goal of GAD is to capture anomalous nodes from graph datasets, which evidently deviate from the majority of nodes. Recent methods have paid attention to various scales of contrastive strategies for GAD, i.e., node-subgraph and node-node contrasts. However, they neglect the subgraph-subgraph comparison information which the normal and abnormal subgraph pairs behave differently in terms of embeddings and structures in GAD, resulting in sub-optimal task performance. In this paper, we fulfill the above idea in the proposed multi-view multi-scale contrastive learning framework with subgraph-subgraph contrast for the first practice. To be specific, we regard the original input graph as the first view and generate the second view by graph augmentation with edge modifications. With the guidance of maximizing the similarity of the subgraph pairs, the proposed subgraph-subgraph contrast contributes to more robust subgraph embeddings despite of the structure variation. Moreover, the introduced subgraph-subgraph contrast cooperates well with the widely-adopted node-subgraph and node-node contrastive counterparts for mutual GAD performance promotions. Besides, we also conduct sufficient experiments to investigate the impact of different graph augmentation approaches on detection performance. The comprehensive experimental results well demonstrate the superiority of our method compared with the state-of-the-art approaches and the effectiveness of the multi-view subgraph pair contrastive strategy for the GAD task.

图神经网络（GNN）是一类流行的机器学习模型。受到学习解释（L2X）范式的启发，我们提出了L2XGNN，这是一个可解释的GNN的框架，该框架通过设计提供了忠实的解释。L2XGNN学习了一种选择解释性子图（主题）的机制，该机制仅在GNNS消息通话操作中使用。L2XGNN能够为每个输入图选择具有特定属性的子图，例如稀疏和连接。对主题施加这种限制通常会导致更容易解释和有效的解释。几个数据集的实验表明，L2XGNN使用整个输入图实现了与基线方法相同的分类精度，同时确保仅使用提供的解释来进行预测。此外，我们表明L2XGNN能够识别负责预测图形属性的主题。

Many applications of machine learning require a model to make accurate predictions on test examples that are distributionally different from training ones, while task-specific labels are scarce during training. An effective approach to this challenge is to pre-train a model on related tasks where data is abundant, and then fine-tune it on a downstream task of interest. While pre-training has been effective in many language and vision domains, it remains an open question how to effectively use pre-training on graph datasets. In this paper, we develop a new strategy and self-supervised methods for pre-training Graph Neural Networks (GNNs). The key to the success of our strategy is to pre-train an expressive GNN at the level of individual nodes as well as entire graphs so that the GNN can learn useful local and global representations simultaneously. We systematically study pre-training on multiple graph classification datasets. We find that naïve strategies, which pre-train GNNs at the level of either entire graphs or individual nodes, give limited improvement and can even lead to negative transfer on many downstream tasks. In contrast, our strategy avoids negative transfer and improves generalization significantly across downstream tasks, leading up to 9.4% absolute improvements in ROC-AUC over non-pre-trained models and achieving state-of-the-art performance for molecular property prediction and protein function prediction.However, pre-training on graph datasets remains a hard challenge. Several key studies (

图形神经网络是一种强大的深度学习工具，用于建模图形结构化数据，在众多图形学习任务上表现出了出色的性能。为了解决深图学习中的数据噪声和数据稀缺性问题，最近有关图形数据的研究已加剧。但是，常规数据增强方法几乎无法处理具有多模式性的非欧几里得空间中定义的图形结构化数据。在这项调查中，我们正式提出了图数据扩展的问题，并进一步审查了代表性技术及其在不同深度学习问题中的应用。具体而言，我们首先提出了图形数据扩展技术的分类法，然后通过根据增强信息方式对相关工作进行分类，从而提供结构化的审查。此外，我们总结了以数据为中心的深图学习中两个代表性问题中图数据扩展的应用：（1）可靠的图形学习，重点是增强输入图的实用性以及通过图数据增强的模型容量； （2）低资源图学习，其针对通过图数据扩大标记的训练数据量表的目标。对于每个问题，我们还提供层次结构问题分类法，并审查与图数据增强相关的现有文献。最后，我们指出了有希望的研究方向和未来研究的挑战。

Generalizable, transferrable, and robust representation learning on graph-structured data remains a challenge for current graph neural networks (GNNs). Unlike what has been developed for convolutional neural networks (CNNs) for image data, self-supervised learning and pre-training are less explored for GNNs. In this paper, we propose a graph contrastive learning (GraphCL) framework for learning unsupervised representations of graph data. We first design four types of graph augmentations to incorporate various priors. We then systematically study the impact of various combinations of graph augmentations on multiple datasets, in four different settings: semi-supervised, unsupervised, and transfer learning as well as adversarial attacks. The results show that, even without tuning augmentation extents nor using sophisticated GNN architectures, our GraphCL framework can produce graph representations of similar or better generalizability, transferrability, and robustness compared to state-of-the-art methods. We also investigate the impact of parameterized graph augmentation extents and patterns, and observe further performance gains in preliminary experiments. Our codes are available at: https://github.com/Shen-Lab/GraphCL.

无监督的图形表示学习是图形数据的非琐碎主题。在结构化数据的无监督代表学习中对比学习和自我监督学习的成功激发了图表上的类似尝试。使用对比损耗的当前无监督的图形表示学习和预培训主要基于手工增强图数据之间的对比度。但是，由于不可预测的不变性，图数据增强仍然没有很好地探索。在本文中，我们提出了一种新颖的协作图形神经网络对比学习框架（CGCL），它使用多个图形编码器来观察图形。不同视图观察的特征充当了图形编码器之间对比学习的图表增强，避免了任何扰动以保证不变性。 CGCL能够处理图形级和节点级表示学习。广泛的实验表明CGCL在无监督的图表表示学习中的优势以及图形表示学习的手工数据增强组合的非必要性。

对比度学习是图表学习中有效的无监督方法。最近，基于数据增强的对比度学习方法已从图像扩展到图形。但是，大多数先前的作品都直接根据为图像设计的模型进行了调整。与图像上的数据增强不同，图表上的数据扩展远不那么直观，而且很难提供高质量的对比样本，这是对比度学习模型的性能的关键。这为改进现有图形对比学习框架留出了很多空间。在这项工作中，通过引入对抗图视图和信息正常化程序，我们提出了一种简单但有效的方法，即对逆向对比度学习（ARIEL），以在合理的约束中提取信息性的对比样本。它始终优于各种现实世界数据集的节点分类任务中当前的图形对比度学习方法，并进一步提高了图对比度学习的鲁棒性。

图形相似性学习是指计算两个图之间的相似性得分，这在许多现实的应用程序（例如视觉跟踪，图形分类和协作过滤）中需要。由于大多数现有的图形神经网络产生了单个图的有效图表，因此几乎没有努力共同学习两个图表并计算其相似性得分。此外，现有的无监督图相似性学习方法主要基于聚类，它忽略了图对中体现的有价值的信息。为此，我们提出了一个对比度图匹配网络（CGMN），以进行自我监督的图形相似性学习，以计算任何两个输入图对象之间的相似性。具体而言，我们分别在一对中为每个图生成两个增强视图。然后，我们采用两种策略，即跨视图相互作用和跨刻画相互作用，以实现有效的节点表示学习。前者求助于两种观点中节点表示的一致性。后者用于识别不同图之间的节点差异。最后，我们通过汇总操作进行图形相似性计算将节点表示形式转换为图形表示。我们已经在八个现实世界数据集上评估了CGMN，实验结果表明，所提出的新方法优于图形相似性学习下游任务的最新方法。

基于图形神经网络（GNN）方法最近已成为处理图数据的流行工具，因为它们能够合并结构信息。GNNS性能的唯一障碍是缺乏标记数据。图像和文本数据的数据增强技术无法用于图形数据，因为图形数据的复杂和非欧几里得结构。这一差距迫使研究人员将注意力转向开发图形数据的数据增强技术。大多数提出的图形数据增强（GDA）技术都是特定于任务的。在本文中，我们根据不同的图形任务调查了现有的GDA技术。这项调查不仅提供了GDA研究界的参考，而且还向其他领域的研究人员提供了必要的信息。

Link prediction is a crucial problem in graph-structured data. Due to the recent success of graph neural networks (GNNs), a variety of GNN-based models were proposed to tackle the link prediction task. Specifically, GNNs leverage the message passing paradigm to obtain node representation, which relies on link connectivity. However, in a link prediction task, links in the training set are always present while ones in the testing set are not yet formed, resulting in a discrepancy of the connectivity pattern and bias of the learned representation. It leads to a problem of dataset shift which degrades the model performance. In this paper, we first identify the dataset shift problem in the link prediction task and provide theoretical analyses on how existing link prediction methods are vulnerable to it. We then propose FakeEdge, a model-agnostic technique, to address the problem by mitigating the graph topological gap between training and testing sets. Extensive experiments demonstrate the applicability and superiority of FakeEdge on multiple datasets across various domains.