Asymmetrical Hierarchical Networks with Attentive Interactions for Interpretable Review-Based Recommendation

Recently, recommender systems have been able to emit substantially improved recommendations by leveraging user-provided reviews. Existing methods typically merge all reviews of a given user or item into a long document, and then process user and item documents in the same manner. In practice, however, these two sets of reviews are notably different: users' reviews reflect a variety of items that they have bought and are hence very heterogeneous in their topics, while an item's reviews pertain only to that single item and are thus topically homogeneous. In this work, we develop a novel neural network model that properly accounts for this important difference by means of asymmetric attentive modules. The user module learns to attend to only those signals that are relevant with respect to the target item, whereas the item module learns to extract the most salient contents with regard to properties of the item. Our multi-hierarchical paradigm accounts for the fact that neither are all reviews equally useful, nor are all sentences within each review equally pertinent. Extensive experimental results on a variety of real datasets demonstrate the effectiveness of our method

GInRec: A Gated Architecture for Inductive Recommendation using Knowledge Graphs

We have witnessed increasing interest in exploiting KGs to integrate contextual knowledge in recommender systems in addition to user-item interactions, e.g., ratings. Yet, most methods are transductive, i.e., they represent instances seen during training as low-dimensionality vectors but cannot do so for unseen instances. Hence, they require heavy retraining every time new items or users are added. Conversely, inductive methods promise to solve these issues. KGs enhance inductive recommendation by offering information on item-entity relationships, whereas existing inductive methods rely purely on interactions, which makes recommendations for users with few interactions sub-optimal and even impossible for new items. In this work, we investigate the actual ability of inductive methods exploiting both the structure and the data represented by KGs. Hence, we propose GInRec, a state-of-the-art method that uses a graph neural network with relation-specific gates and a KG to provide better recommendations for new users and items than related inductive methods. As a result, we re-evaluate state-of-the-art methods, identify better evaluation protocols, highlight unwarranted conclusions from previous proposals, and showcase a novel, stronger architecture for this task. The source code is available at: https://github.com/theisjendal/kars2023-recommendation-framework

Mixed Information Flow for Cross-domain Sequential Recommendations

Cross-domain sequential recommendation is the task of predict the next item that the user is most likely to interact with based on past sequential behavior from multiple domains. One of the key challenges in cross-domain sequential recommendation is to grasp and transfer the flow of information from multiple domains so as to promote recommendations in all domains. Previous studies have investigated the flow of behavioral information by exploring the connection between items from different domains. The flow of knowledge (i.e., the connection between knowledge from different domains) has so far been neglected. In this paper, we propose a mixed information flow network for cross-domain sequential recommendation to consider both the flow of behavioral information and the flow of knowledge by incorporating a behavior transfer unit and a knowledge transfer unit. The proposed mixed information flow network is able to decide when cross-domain information should be used and, if so, which cross-domain information should be used to enrich the sequence representation according to users' current preferences. Extensive experiments conducted on four e-commerce datasets demonstrate that mixed information flow network is able to further improve recommendation performance in different domains by modeling mixed information flow.Comment: 26 pages, 6 figures, TKDD journal, 7 co-author

Effective neural architectures for context-aware venue recommendation

Users in Location-Based Social Networks (LBSNs), such as Yelp and Foursquare, can search for interesting venues such as restaurants and museums to visit, or share their location with their friends by making an implicit feedback (e.g. checking in at venues they have visited). The users can also leave explicit feedback on the venues they have visited by providing rat- ings and/or comments. Such explicit and implicit feedback by the users provide rich infor- mation about both users and venues, and thus can be leveraged to study the users’ movement in urban cities, as well as enhance the quality of personalised venue recommendations. Un- like traditional recommendation systems (e.g. book and movie recommendation systems), making effective venue recommendations is more challenging because we need to take into account the users’ current context (e.g. time of the day, user’s current location as well as his recently visited venues). Two common techniques that are widely used in the literature for venue recommen- dation systems are Matrix Factorisation (MF) and Bayesian Personalised Ranking (BPR). MF is a popular Collaborative Filtering (CF) technique that can leverage the users’ explicit feedback (e.g. the numerical ratings) to predict the users’ ratings on the venues and hence relevant venues can be suggested to the users based on these predicted ratings. On the other hand, BPR is a pairwise ranking-based model that can leverage implicit feedback to generate effective top-K venue recommendations. In this thesis, based upon MF and BPR models, we aim to generate effective context-aware venue recommendation that a user may wish to visit based on the user’s historical explicit and implicit feedbacks, the user’s contextual informa- tion (e.g. the user’s current location and time of the day) and additional information (e.g. the geographical location of venues and users’ social relationships). To achieve this goal, we need to address the following challenges: namely (C1) modelling the users’ preferences and the characteristic of venues, (C2) capturing the complex structure of user-venue inter- actions in a Collaborative Filtering manner, (C3) modelling the users’ short-term (dynamic) preferences from the sequential order of user’s observed feedback as well as the contextual information associated with the successive feedback, (C4) generating accurate top-K venue recommendations based on the users’ preferences using a pairwise ranking-based model and (C5) appropriately sampling potential negative instances to train a ranking-based model. First, to address challenge C1, we leverage the users’ explicit feedback (e.g. their rat- ings and the textual content of the comments) and additional information (e.g. users’ social relationships) to effectively model the users’ preferences and the characteristics of venues. In particular, we propose a novel regularisation technique and a factorisation-based model that leverages the users’ explicit feedback and the additional information to improve the rat- ing prediction accuracy of the traditional MF model. Experiments conducted on a large scale rating dataset on LBSN demonstrate that the textual content of comments plays an important role in enhancing the accuracy of rating prediction. Second, we investigate how to leverage the users’ implicit feedback and additional in- formation such as the users’ social relationship and the geographical location of venues to improve the quality of top-K venue recommendations. We argue that the potential negative instances can be effectively sampled based on the social correlations between users and their friends as well as the geographical influences between the users’ and venues’ geographi- cal location. In particular, to address challenges C4 and C5, we propose a novel pairwise ranking-based framework for top-K venue recommendations that can incorporate multiple sources of additional information (e.g. the users’ social relationship and the geographical location of venues) to effectively sample the potential negative instances. Experimental re- sults on three large scale checkin and rating datasets from LBSNs demonstrate that the social correlations and the geographical influences play an important role to the quality of sampled negative instances and hence can improve the quality of top-K venue recommendations. Finally, to address challenges C2 and C3, we propose a framework for context-aware venue recommendations that exploits Deep Neural Network (DNN) models to effectively capture the complex structure of user-venue interactions and the users’ long-term (dynamic) preferences from their sequential order of checkins. In particular, within the framework, we propose a novel Recurrent Neural Network (RNN) architecture that can effectively in- corporate the contextual information associated with the successive implicit feedback (e.g. the time interval and the geographical distance between two successive checkins) to gener- ate high quality context-aware venue recommendations. Experimental results on three large scale checkin and rating datasets from LBSNs demonstrate the effectiveness and robustness of our proposed framework for context-aware venue recommendations. In particular, the results demonstrate that the sequential order of users’ implicit feedback can be leveraged to effectively improve the effectiveness of context-aware venue recommendation system. In addition, the time intervals and the geographical distances between two successive checkins play an important role in capturing the users’ short-term preferences

HTP: Exploiting Holistic Temporal Patterns for Sequential Recommendation

Sequential recommender systems have demonstrated a huge success for next-item recommendation by explicitly exploiting the temporal order of users' historical interactions. In practice, user interactions contain more useful temporal information beyond order, as shown by some pioneering studies. In this paper, we systematically investigate various temporal information for sequential recommendation and identify three types of advantageous temporal patterns beyond order, including absolute time information, relative item time intervals and relative recommendation time intervals. We are the first to explore item-oriented absolute time patterns. While existing models consider only one or two of these three patterns, we propose a novel holistic temporal pattern based neural network, named HTP, to fully leverage all these three patterns. In particular, we introduce novel components to address the subtle correlations between relative item time intervals and relative recommendation time intervals, which render a major technical challenge. Extensive experiments on three real-world benchmark datasets show that our HTP model consistently and substantially outperforms many state-of-the-art models. Our code is publically available at https://github.com/623851394/HTP/tree/main/HTP-mai

Leveraging Large Language Models for Pre-trained Recommender Systems

Recent advancements in recommendation systems have shifted towards more comprehensive and personalized recommendations by utilizing large language models (LLM). However, effectively integrating LLM's commonsense knowledge and reasoning abilities into recommendation systems remains a challenging problem. In this paper, we propose RecSysLLM, a novel pre-trained recommendation model based on LLMs. RecSysLLM retains LLM reasoning and knowledge while integrating recommendation domain knowledge through unique designs of data, training, and inference. This allows RecSysLLM to leverage LLMs' capabilities for recommendation tasks in an efficient, unified framework. We demonstrate the effectiveness of RecSysLLM on benchmarks and real-world scenarios. RecSysLLM provides a promising approach to developing unified recommendation systems by fully exploiting the power of pre-trained language models.Comment: 13 pages, 4 figure

Improving Items and Contexts Understanding with Descriptive Graph for Conversational Recommendation

State-of-the-art methods on conversational recommender systems (CRS) leverage external knowledge to enhance both items' and contextual words' representations to achieve high quality recommendations and responses generation. However, the representations of the items and words are usually modeled in two separated semantic spaces, which leads to misalignment issue between them. Consequently, this will cause the CRS to only achieve a sub-optimal ranking performance, especially when there is a lack of sufficient information from the user's input. To address limitations of previous works, we propose a new CRS framework KLEVER, which jointly models items and their associated contextual words in the same semantic space. Particularly, we construct an item descriptive graph from the rich items' textual features, such as item description and categories. Based on the constructed descriptive graph, KLEVER jointly learns the embeddings of the words and items, towards enhancing both recommender and dialog generation modules. Extensive experiments on benchmarking CRS dataset demonstrate that KLEVER achieves superior performance, especially when the information from the users' responses is lacking.Comment: 14 pages, 3 figures, 9 table