Handling Information Loss of Graph Neural Networks for Session-based Recommendation

Recently, graph neural networks (GNNs) have gained increasing popularity due to their convincing performance in various applications. Many previous studies also attempted to apply GNNs to session-based recommendation and obtained promising results. However, we spot that there are two information loss problems in these GNN-based methods for session-based recommendation, namely the lossy session encoding problem and the ineffective long-range dependency capturing problem. The first problem is the lossy session encoding problem. Some sequential information about item transitions is ignored because of the lossy encoding from sessions to graphs and the permutation-invariant aggregation during message passing. The second problem is the ineffective long-range dependency capturing problem. Some long-range dependencies within sessions cannot be captured due to the limited number of layers. To solve the first problem, we propose a lossless encoding scheme and an edge-order preserving aggregation layer based on GRU that is dedicatedly designed to process the losslessly encoded graphs. To solve the second problem, we propose a shortcut graph attention layer that effectively captures long-range dependencies by propagating information along shortcut connections. By combining the two kinds of layers, we are able to build a model that does not have the information loss problems and outperforms the state-of-the-art models on three public datasets.