Sequential recommendation models are crucial for next-item prediction tasks in various online platforms, yet many focus on a single behavior, neglecting valuable implicit interactions. While multi-behavioral models address this using graph-based approaches, they often fail to capture sequential patterns simultaneously. Our proposed Multi-Behavioral Sequential Recommendation framework (MBSRec) captures the multi-behavior dependencies between the heterogeneous historical interactions via multi-head self-attention. Furthermore, we utilize a weighted binary cross-entropy loss for precise behavior control. Experimental results on four datasets demonstrate MBSRec’s significant outperformance of state-of-the-art approaches. The implementation code is available here 1.

In sparse recommender settings, users’ context and item attributes play a crucial role in deciding which items to recommend next. Despite that, recent works in sequential and time-aware recommendations usually either ignore both aspects or only consider one of them, limiting their predictive performance. In this paper, we address these limitations by proposing a context and attribute-aware recommender model (CARCA) that can capture the dynamic nature of the user profiles in terms of contextual features and item attributes via dedicated multi-head self-attention blocks that extract profile-level features and predict item scores. Also, unlike many of the current state-of-the-art sequential item recommendation approaches that use a simple dot-product between the most recent item’s latent features and the target items embeddings for scoring, CARCA uses cross-attention between all profile items and the target items to predict their final scores. This cross-attention allows CARCA to harness the correlation between old and recent items in the user profile and their influence on deciding which item to recommend next. Experiments on four real-world recommender system datasets show that the proposed model significantly outperforms all state-of-the-art models in the task of item recommendation and achieving improvements of up to 53% in Normalized Discounted Cumulative Gain (NDCG) and Hit-Ratio. Results also show that CARCA outperformed several state-of-the-art dedicated image-based recommender systems by merely utilizing image attributes extracted from a pre-trained ResNet50 in a black-box fashion.

Normalized discounted cumulative gain (NDCG) is one of the popular evaluation metrics for recommender systems and learning-to-rank problems. As it is non-differentiable, it cannot be optimized by gradient-based optimization procedures. In the last twenty years, a plethora of surrogate losses have been engineered that aim to make learning recommendation and ranking models that optimize NDCG possible. However, binary relevance implicit feedback settings still pose a significant challenge for such surrogate losses as they are usually designed and evaluated only for multi-level relevance feedback. In this paper, we address the limitations of directly optimizing the NDCG measure by proposing a guided learning approach (GuidedRec) that adopts recent advances in parameterized surrogate losses for NDCG. Starting from the observation that jointly learning a surrogate loss for NDCG and the recommendation model is very unstable, we design a stepwise approach that can be seamlessly applied to any recommender system model that uses a point-wise logistic loss function. The proposed approach guides the models towards optimizing the NDCG using an independent surrogate-loss model trained to approximate the true NDCG measure while maintaining the original logistic loss function as a stabilizer for the guiding procedure. In experiments on three recommendation datasets, we show that our guided surrogate learning approach yields models better optimized for NDCG than recent state-of-the-art approaches using engineered surrogate losses.

In auction-based systems such as in used car centers and online auction websites, users usually bid on items, and those items get sold to their highest bidders. In these settings, every item is unique and can be sold only once, which means users’ purchase histories will be unique, and no common items will exist across them. On the other hand, items will not have any historical sales at all. Such extreme settings pose a significant challenge to the current recommender systems models that rely on historical user-item interactions. While some of those models will not be applicable altogether, such as the matrix factorization models, neighborhood models, and even the naive most-popular model, the rest will need to rely only on items’ attributes. In this paper, we address the challenges of auction-based item recommendation by proposing a simple multi-relational recommender model (MultiRec) that can seamlessly leverage user and item attributes along with auxiliary relational information such as the user’s bidding history. Experiments on one proprietary dataset from Volkswagen Financial Services used-cars center, and on a real-world publicly available eBay dataset show that the proposed model significantly outperforms multiple state-of-art models in the task of auction-based unique item recommendation.

Multi-task learning is an established approach for improving the generalization of a model. We explore multi-task learning in the context of time series forecasting. Specifically, we look into a multivariate setting where main and auxiliary series are to be forecasted for multi-step ahead. This results in an interesting multi-task learning problem formulation where the learning tasks come from future horizon of main and auxiliary series both. Our proposed method relies firstly on enumerating multiple Convolutional network architectures to balance the number of shared and non-shared layers between different time series tasks. Also, as multi-step strategies minimize forecast errors over the complete horizon, loss functions would be at different scales based on model uncertainty for near versus distant future. For this reason we propose a factorization of the weight vector for the learning tasks with respect to their categorization of belonging to main or auxiliary series and index in future. An optimal number of shared and non-shared layers together with a novel weighted loss, results in superior performance over 2 real-world datasets compared with several baselines.

The task of classifying multi-relational data spans a wide range of domains such as document classification in citation networks, classification of emails, and protein labeling in proteins interaction graphs. Current state-of-the-art classification models rely on learning per-entity latent representations by mining the whole structure of the relations' graph, however, they still face two major problems. Firstly, it is very challenging to generate expressive latent representations in sparse multi-relational settings with implicit feedback relations as there is very little information per-entity. Secondly, for entities with structured properties such as titles and abstracts (text) in documents, models have to be modified ad-hoc. In this paper, we aim to overcome these two main drawbacks by proposing a flexible nonlinear latent embedding model (BRNLE) for the classification of multi-relational data. The proposed model can be applied to entities with structured properties such as text by utilizing the numerical vector representations of those properties. To address the sparsity problem of implicit feedback relations, the model is optimized via a sparsely-regularized multi-relational pair-wise Bayesian personalized ranking loss (BPR). Experiments on four different real-world datasets show that the proposed model significantly outperforms state-of-the-art models for multi-relational classification.

In very sparse recommender data sets, attributes of users such as age, gender and home location and attributes of items such as, in the case of movies, genre, release year, and director can improve the recommendation accuracy, especially for users and items that have few ratings. While most recommendation models can be extended to take attributes of users and items into account, their architectures usually become more complicated. While attributes for items are often easy to be provided, attributes for users are often scarce for reasons of privacy or simply because they are not relevant to the operational process at hand. In this paper, we address these two problems for attribute-aware recommender systems by proposing a simple model that co-embeds users and items into a joint latent space in a similar way as a vanilla matrix factorization, but with non-linear latent features construction that seamlessly can ingest user or item attributes or both (GraphRec). To address the second problem, scarce attributes, the proposed model treats the user-item relation as a bipartite graph and constructs generic user and item attributes via the Laplacian of the user-item co-occurrence graph that requires no further external side information but the mere rating matrix. In experiments on three recommender datasets, we show that GraphRec significantly outperforms existing state-of-the-art attribute-aware and content-aware recommender systems even without using any side information.