Session-based recommendation aims to predict the user's next action based on anonymous sessions without using side information. Most of the real-world session datasets are sparse and have long-tail item distribution. Although long-tail item recommendation plays a crucial role in improving user satisfaction, only a few methods have been proposed to take the long-tail session recommendation into consideration. Previous works in handling data sparsity problems are mostly limited to self-supervised learning techniques with heuristic augmentation which can ruin the original characteristic of session datasets, sequential and co-occurrences, and make noisier short sessions by dropping items and cropping sequences. We propose a novel method, LOAM, improving LOng-tail session-based recommendation via niche walk Augmentation and tail session Mixup, that alleviates popularity bias and enhances long-tail recommendation performance. LOAM consists of two modules, Niche Walk Augmentation (NWA) and Tail Session Mixup (TSM). NWA can generate synthetic sessions considering long-tail distribution which are likely to be found in original datasets, unlike previous heuristic methods, and expose a recommender model to various item transitions with global information. This improves the item coverage of recommendations. TSM makes the model more generalized and robust by interpolating sessions at the representation level. It encourages the recommender system to predict niche items with more diversity and relevance. We conduct extensive experiments with four real-world datasets and verify that our methods greatly improve tail performance while balancing overall performance.

Session-based recommendation predicts an anonymous user’s next action, whether she or he is likely to purchase based on the user’s behavior in the current session as sequences. Most recent research on session-based recommendations makes predictions based on a single-session without incorporating global relationships between sessions. It does not guarantee a better performance because item embeddings learned by solely utilizing a single session (inter-session) have less item transition information than utilizing both intra- and inter-session ones. Some existing methods tried to enhance recommendation performance by adopting memory modules and global transition graphs; however, those need more computation cost and time. We propose a novel algorithm called Logit Averaging (LA), utilizing both (i) local-level logits, which come from intra-sessions item transitions and (ii) global-level logits, which come from gathered logits of related sessions. The proposed method shows an improvement in recommendation performance in respect of accuracy and diversity through extensive experiments.

여러 사회 분야에서 빅데이터와 컴퓨팅 기술의 발전을 기반으로 인공지능 기술의 도입이 활발히 이루어지고 있다. 하지만 빅데이터에 내재되어 있는 사회적인 차별요소로 인하여 인공지능의 예측이 편향된 경우가 많아 공정성 논란이 발생하고 있다. 특히, 소셜 네트워크 데이터를 다루기에 적당한 그래프 신경망에서는 유사한 노드들을 연결하려는 동질성 효과(Homophily effect) 때문에 성별, 종교 등과 같은 민감한 속성(Sensitive Attribute)에 편향된 예측이 이루어지기 쉬워서 공정성 문제가 더욱 심각하다. 이러한 공정성 문제를 해결하기 위하여, 공정한 모델 연구와 편향된 정도를 평가하기 위한 공정성 지표들이 제안되고 있다. 그러나 관련 연구들에서 각기 다른 지표를 사용해 공정성을 평가하기 때문에 통일된 기준이 없고, 모델의 정확성과 공정성이 상충관계(trade-off)에 있음을 고려하지 않아 두 성능 모두를 고려한 판단 지표가 필요하다. 본 논문은 공정성과 정확도의 관계를 고려한 지표인 FairSUBβ/SUB-metric을 제안하고, 이 지표에서 우수한 성능을 내는 그래프 링크 예측 모델 FairU를 제안한다.