Region or Global? A Principle for Negative Sampling in Graph-Based Recommendation

Zhen Yang, Ming Ding, Xu Zou, Jie Tang, Bin Xu, Chang Zhou, Hongxia Yang

Abstract: Graph-based recommendation systems are blossoming recently, which models user-item interactions as a user-item graph and utilizes graph neural networks (GNNs) to learn the embeddings for users and items. A fundamental challenge of graph-based recommendation is that there only exists observed positive user-item pairs in the user-item graph. Negative sampling is a vital technique to solve the one-class problem and is widely used in many recommendation methods. However, the previous works only focus on the design of negative sampling distribution but ignore the sampled region for negative sampling. In this work, we propose <i>the Three-Region Principle</i> to guide negative sampling, which suggests that we should negatively sample more items at an intermediate region and less adjacent and distant items. In light of this principle, we present the RecNS method, which is a general negative sampling method designed with two sampling strategies: positive-assisted sampling and exposure-augmented sampling. Instead of sampling existing negative items from graph data, we merge these two strategies in embedding space to generate negative item embeddings. Extensive experiments demonstrate that RecNS method significantly outperforms all negative sampling baselines, e.g., <inline-formula><tex-math notation="LaTeX">$10.47\%$</tex-math></inline-formula> for PinSage, <inline-formula><tex-math notation="LaTeX">$6.02\%$</tex-math></inline-formula> for NGCF, and <inline-formula><tex-math notation="LaTeX">$8.20\%$</tex-math></inline-formula> for LightGCN in terms of Recall@20 on the Alibaba dataset.