Rethinking the Denoising Strategy in Session-Based Recommendation via Bidirectional Information Flow

Abstract Session-based recommendation (SBR) focuses on predicting the next potential item for anonymous users based on short-click sessions. However, these interaction sessions often contain noise items, which arise from misclicks or shifts in user interests. Existing denoising methods typically presume a strong exclusionary relationship between noise items and the recommendation target, assuming that reducing noise can enhance recommendation accuracy. In contrast, our observations reveal a nuanced phenomenon: as the length of the interaction session shortens, the effect of noise removal on recommendation performance gradually transitions from positive to negative. This finding suggests that in short sessions with insufficient contextual information, relying solely on the exclusion of noise items within the session may fail to improve and could even hinder-the recommendation performance. Such complexities have been largely overlooked in prior research. To bridge this gap, we propose two solutions: (i) expanding the view of denoising from a single session to multiple sessions (i.e., from local to global), and (ii) introducing relevant contextual information into each session by employing enhancement strategies. Therefore, we design the Hybrid Prototype-based In-and-Out Flow Network (HyPro), which employs both denoising and enhancing processes for each session based on our proposed hybrid prototypes. Specifically, for each item, HyPro first learns the hybrid prototype by aggregating information from the item’s semantic and topological neighbors across all sessions. Then, based on the hybrid prototypes, HyPro employs an in-and-out flow network comprising two components: (i) the out-flow channel, which targets the removal of irrelevant information at both the data and feature levels, and (ii) the in-flow channel, which integrates global information for each session at the item and session levels. Extensive experiments conducted on three real-world datasets demonstrate that HyPro outperforms the state-of-the-art baselines. The implementation code is available at: https://github.com/jarviswww/Code4HyPro .