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Title: Graph inference learning for semi-supervised classification

Paper content:
In this work, we address the semi-supervised classification of graph data, where the categories of those unlabeled nodes are inferred from labeled nodes as well as graph structures.
Recent works often solve this problem with the advanced graph convolution in a conventional supervised manner, but the performance could be heavily affected when labeled data is scarce.
Here we propose a Graph Inference Learning (GIL) framework to boost the performance of node classification by learning the inference of node labels on graph topology.
To bridge the connection of two nodes, we formally define a structure relation by encapsulating node attributes, between-node paths and local topological structures together, which can make inference conveniently deduced from one node to another node.
For learning the inference process, we further introduce meta-optimization on structure relations from training nodes to validation nodes, such that the learnt graph inference capability can be better self-adapted into test nodes.
Comprehensive evaluations on four benchmark datasets (including Cora, Citeseer, Pubmed and NELL) demonstrate the superiority of our GIL when compared with other state-of-the-art methods in the semi-supervised node classification task.
Graph, which comprises a set of vertices/nodes together with connected edges, is a formal structural representation of non-regular data.
Due to the strong representation ability, it accommodates many potential applications, e.g., social network (Orsini et al., 2017) , world wide data (Page et al., 1999) , knowledge graph (Xu et al., 2017) , and protein-interaction network (Borgwardt et al., 2007) .
Among these, semi-supervised node classification on graphs is one of the most interesting also popular topics.
Given a graph in which some nodes are labeled, the aim of semi-supervised classification is to infer the categories of those remaining unlabeled nodes by using various priors of the graph.
While there have been numerous previous works (Brandes et al., 2008; Zhou et al., 2004; Zhu et al., 2003; Yang et al., 2016; Zhao et al., 2019) devoted to semi-supervised node classification based on explicit graph Laplacian regularizations, it is hard to efficiently boost the performance of label prediction due to the strict assumption that connected nodes are likely to share the same label information.
With the progress of deep learning on grid-shaped images/videos (He et al., 2016) , a few of graph convolutional neural networks (CNN) based methods, including spectral (Kipf & Welling, 2017) and spatial methods (Niepert et al., 2016; Pan et al., 2018; Yu et al., 2018) , have been proposed to learn local convolution filters on graphs in order to extract more discriminative node representations.
Although graph CNN based methods have achieved considerable capabilities of graph embedding by optimizing filters, they are limited into a conventionally semi-supervised framework and lack of an efficient inference mechanism on graphs.
Especially, in the case of few-shot learning, where a small number of training nodes are labeled, this kind of methods would drastically compromise the performance.
For example, the Pubmed graph dataset (Sen et al., 2008) consists (b) The process of Graph inference learning.
We extract the local representation from the local subgraph (the circle with dashed line The red wave line denote the node reachability from to .
d t th h bilit f d t th d
Figure 1: The illustration of our proposed GIL framework.
For the problem of graph node labeling, the category information of these unlabeled nodes depends on the similarity computation between a query node (e.g., vj) and these labeled reference nodes (e.g., vi).
We consider the similarity from three points: node attributes, the consistency of local topological structures (i.e., the circle with dashed line), and the between-node path reachability (i.e., the red wave line from vi to vj).
Specifically, the local structures as well as node attributes are encoded as high-level features with graph convolution, while the between-node path reachability is abstracted as reachable probabilities of random walks.
To better make the inference generalize to test nodes, we introduce a meta-learning strategy to optimize the structure relations learning from training nodes to validation nodes.
of 19,717 nodes and 44,338 edges, but only 0.3% nodes are labeled for the semi-supervised node classification task.
These aforementioned works usually boil down to a general classification task, where the model is learnt on a training set and selected by checking a validation set.
However, they do not put great efforts on how to learn to infer from one node to another node on a topological graph, especially in the few-shot regime.
In this paper, we propose a graph inference learning (GIL) framework to teach the model itself to adaptively infer from reference labeled nodes to those query unlabeled nodes, and finally boost the performance of semi-supervised node classification in the case of a few number of labeled samples.
Given an input graph, GIL attempts to infer the unlabeled nodes from those observed nodes by building between-node relations.
The between-node relations are structured as the integration of node attributes, connection paths, and graph topological structures.
It means that the similarity between two nodes is decided from three aspects: the consistency of node attributes, the consistency of local topological structures, and the between-node path reachability, as shown in Fig. 1 .
The local structures anchored around each node as well as the attributes of nodes therein are jointly encoded with graph convolution (Defferrard et al., 2016) for the sake of high-level feature extraction.
For the between-node path reachability, we adopt the random walk algorithm to obtain the characteristics from a labeled reference node v i to a query unlabeled node v j in a given graph.
Based on the computed node representation and between-node reachability, the structure relations can be obtained by computing the similar scores/relationships from reference nodes to unlabeled nodes in a graph.
Inspired by the recent meta-learning strategy (Finn et al., 2017) , we learn to infer the structure relations from a training set to a validation set, which can benefit the generalization capability of the learned model.
In other words, our proposed GIL attempts to learn some transferable knowledge underlying in the structure relations from training samples to validation samples, such that the learned structure relations can be better self-adapted to the new testing stage.
We summarize the main contributions of this work as three folds:
• We propose a novel graph inference learning framework by building structure relations to infer unknown node labels from those labeled nodes in an end-to-end way.
The structure relations are well defined by jointly considering node attributes, between-node paths, and graph topological structures.
• To make the inference model better generalize to test nodes, we introduce a meta-learning procedure to optimize structure relations, which could be the first time for graph node classification to the best of our knowledge.
• Comprehensive evaluations on three citation network datasets (including Cora, Citeseer, and Pubmed) and one knowledge graph data (i.e., NELL) demonstrate the superiority of our proposed GIL in contrast with other state-of-the-art methods on the semi-supervised classification task.
In this work, we tackled the semi-supervised node classification task with a graph inference learning method, which can better predict the categories of these unlabeled nodes in an end-to-end framework.
We can build a structure relation for obtaining the connection between any two graph nodes, where node attributes, between-node paths, and graph structure information can be encapsulated together.
For better capturing the transferable knowledge, our method further learns to transfer the mined knowledge from the training samples to the validation set, finally boosting the prediction accuracy of the labels of unlabeled nodes in the testing set.
The extensive experimental results demonstrate the effectiveness of our proposed GIL for solving the semi-supervised learning problem, even in the few-shot paradigm.
In the future, we would extend the graph inference method to handle more graph-related tasks, such as graph generation and social network analysis.

assistant: text: We propose a novel graph inference learning framework by building structure relations to infer unknown node labels from those labeled nodes in an end-to-end way.