Group recommendation has become highly demanded when users communicate in the forms of group activities in online sharing communities. These group activities include student group study, family TV program watching, friends travel decision, etc. Existing group recommendation techniques mainly focus on the small user groups. However, online sharing communities have enabled group activities among thousands of users. Accordingly, recommendation over large groups has become urgent. In this paper, we propose a new framework to accomplish this goal by exploring the group interests and the connections between group users. We first divide a big group into different interest subgroups, each of which contains users closely connected with each other and sharing the similar interests. Then, for each interest subgroup, our framework exploits the connections between group users to collect a comparably compact potential candidate set of media-user pairs, on which the collaborative filtering is performed to generate an interest subgroup-based recommendation list. After that, a novel aggregation function is proposed to integrate the recommended media lists of all interest subgroups as the final group recommendation results. Extensive experiments have been conducted on two real social media datasets to demonstrate the effectiveness and efficiency of our proposed approach.

Recommender systems (RS) play an integral role in many online platforms. Exponential growth and potential commercial interests are raising significant concerns around privacy, security, fairness, and overall responsibility. The existing literature around responsible recommendation services is diverse and multidisciplinary. Most literature reviews cover a specific aspect or a single technology for responsible behavior, such as federated learning or blockchain. This study integrates relevant concepts across disciplines to provide a broader representation of the landscape. We review the latest advancements toward building privacy-preserved and responsible recommendation services for the e-commerce industry. The survey summarizes recent, high-impact works on diverse aspects and technologies that ensure responsible behavior in RS through an interconnected taxonomy. We contextualize potential privacy threats, practical significance, industrial expectations, and research remedies. From the technical viewpoint, we analyze conventional privacy defenses and provide an overview of emerging technologies including differential privacy, federated learning, and blockchain. The methods and concepts across technologies are linked based on their objectives, challenges, and future directions. In addition, we also develop an open source repository that summarizes a wide range of evaluation benchmarks, codebases, and toolkits to aid the further research. The survey offers a holistic perspective on this rapidly evolving landscape by synthesizing insights from both RS and responsible AI literature.

Personalized federated learning (PFL) is a subfield of federated learning. Contrary to conventional federated learning that expects to find a general global model, PFL generates a personalized model adapted to its local data distribution for each client. Some existing PFL methods only consider improving the client-side personalization ability, discarding the server-side generalization capacity. To address this issue, we propose a fine-tuning and head aggregation method in federated learning (FedFTHA). It allows each client to maintain a personalized model head and fine-tune it after each local update to generate a local model containing the personalized head. Specifically, during FedFTHA training, these personalized heads are aggregated to generate a generalized head for the global model. FedFTHA meets the needs of both client-side model personalization and server-side model generalization. In addition, a universal optimization framework is employed to prove its convergence under convex and nonconvex conditions. We verify the personalization ability and generalization performance of FedFTHA under heterogeneous settings with benchmark data sets. The comparative analysis authenticates the significance of our proposal.