ProtoCF: Prototypical Collaborative Filtering for Few-shot Recommendation

Aravind Sankar, Junting Wang, Adit Krishnan, Hari Sundaram
Conference PaperRecSys 2021: Fifteenth ACM Conference on Recommender Systems, Virtual Event, Brazil, September 22-26, 2020


In recent times, deep learning methods have supplanted conventional collaborative filtering approaches as the backbone of modern recommender systems. However, their gains are skewed towards popular items with a drastic performance drop for the vast collection of long-tail items with sparse interactions. Moreover, we empirically show that prior neural recommenders lack the resolution power to accurately rank relevant items within the long-tail. In this paper, we formulate long-tail item recommendations as a few-shot learning problem of learning-to-recommend few-shot items with very few interactions.We propose a novel meta-learning framework ProtoCF that learns-to-compose robust prototype representations for few-shot items. ProtoCF utilizes episodic few-shot learning to extract meta-knowledge across a collection of diverse meta-training tasks designed to mimic item ranking within the tail. To further enhance discriminative power, we propose a novel architecture-agnostic technique based on knowledge distillation to extract, relate, and transfer knowledge from neural base recommenders. Our experimental results demonstrate that ProtoCF consistently outperforms state-of-art approaches on overall recommendation (by 5% Recall@50) while achieving significant gains (of 60-80% Recall@50) for tail items with less than 20 interactions.

Graph Neural Networks for Friend Ranking in Large-scale Social Platforms

Aravind Sankar, Yozen Liu, Jun Yu, Neil Shah
Conference PaperProceedings of The Web Conference 2021, WWW 2021, Ljubljana, Slovenia, April 2021


Graph Neural Networks (GNNs) have recently enabled substantial advances in graph learning. Despite their rich representational capacity, GNNs remain under-explored for large-scale social modeling applications. One such industrially ubiquitous application is friend suggestion: recommending users other candidate users to befriend, to improve user connectivity, retention and engagement. However, modeling such user-user interactions on large-scale social platforms poses unique challenges: such graphs often have heavy-tailed degree distributions, where a significant fraction of users are inactive and have limited structural and engagement information. Moreover, users interact with different functionalities, communicate with diverse groups, and have multifaceted interaction patterns. We study the application of GNNs for friend suggestion, providing the first investigation of GNN design for this task, to our knowledge. To leverage the rich knowledge of in-platform actions, we formulate friend suggestion as multi-faceted friend ranking with multi-modal user features and link communication features. We design a neural architecture GraFRank to learn expressive user representations from multiple feature modalities and user-user interactions. Specifically, GraFRank employs modality-specific neighbor aggregators and cross-modality attentions to learn multi-faceted user representations. We conduct experiments on two multi-million user datasets from Snapchat, a leading mobile social platform, where GraFRank outperforms several state-of-the-art approaches on candidate retrieval (by 30% MRR) and ranking (by 20% MRR) tasks. Moreover, our qualitative analysis indicates notable gains for critical populations of less-active and low-degree users.

Beyond Localized Graph Neural Networks: An Attributed Motif Regularization Framework

Aravind Sankar, Junting Wang, Adit Krishnan, Hari Sundaram
Conference Paper2020 IEEE International Conference on Data Mining (ICDM), ICDM 2020, November 17-20, 2020


We present InfoMotif, a new semi-supervised, motif-regularized, learning framework over graphs. We overcome two key limitations of message passing in popular graph neural networks (GNNs): localization (a k-layer GNN cannot utilize features outside the k-hop neighborhood of the labeled training nodes) and over-smoothed (structurally indistinguishable) representations. We propose the concept of attributed structural roles of nodes based on their occurrence in different network motifs, independent of network proximity. Two nodes share attributed structural roles if they participate in topologically similar motif instances over co-varying sets of attributes. Further, InfoMotif achieves architecture independence by regularizing the node representations of arbitrary GNNs via mutual information maximization. Our training curriculum dynamically prioritizes multiple motifs in the learning process without relying on distributional assumptions in the underlying graph or the learning task. We integrate three state-of-the-art GNNs in our framework, to show significant gains (3-10% accuracy) across six diverse, real-world datasets. We see stronger gains for nodes with sparse training labels and diverse attributes in local neighborhood structures.

GroupIM: A Mutual Information Maximization Framework for Neural Group Recommendation

Aravind Sankar, Yanhong Wu, Yuhang Wu, Wei Zhang, Hao Yang, Hari Sundaram
Conference PaperInternational ACM SIGIR Conference on Research and Development in Information Retrieval, SIGIR 2020, July 25-30, 2020


We study the problem of making item recommendations to ephemeral groups, which comprise users with limited or no historical activities together. Existing studies target persistent groups with substantial activity history, while ephemeral groups lack historical interactions. To overcome group interaction sparsity, we propose data-driven regularization strategies to exploit both the preference covariance amongst users who are in the same group, as well as the contextual relevance of users' individual preferences to each group. We make two contributions. First, we present a recommender architecture-agnostic framework GroupIM that can integrate arbitrary neural preference encoders and aggregators for ephemeral group recommendation. Second, we regularize the user-group latent space to overcome group interaction sparsity by: maximizing mutual information between representations of groups and group members; and dynamically prioritizing the preferences of highly informative members through contextual preference weighting. Our experimental results on several real-world datasets indicate significant performance improvements (31-62% relative NDCG@20) over state-of-the-art group recommendation techniques.

Inf-VAE: A Variational Autoencoder Framework to Integrate Homophily and Influence in Diffusion Prediction

Aravind Sankar, Xinyang Zhang, Adit Krishnan, Jiawei Han
Conference PaperInternational Conference on Web Search and Data Mining, WSDM 2020, Houston, TX, February 3-7, 2020


Recent years have witnessed tremendous interest in understanding and predicting information spread on social media platforms such as Twitter, Facebook, etc. Existing diffusion prediction methods primarily exploit the sequential order of influenced users by projecting diffusion cascades onto their local social neighborhoods. However, this fails to capture global social structures that do not explicitly manifest in any of the cascades, resulting in poor performance for inactive users with limited historical activities. In this paper, we present a novel variational autoencoder framework (Inf-VAE) to jointly embed homophily and influence through proximity-preserving social and position-encoded temporal latent variables. To model social homophily, Inf-VAE utilizes powerful graph neural network architectures to learn social variables that selectively exploit the social connections of users. Given a sequence of seed user activations, Inf-VAE uses a novel expressive co-attentive fusion network that jointly attends over their social and temporal variables to predict the set of all influenced users. Our experimental results on multiple real-world social network datasets, including Digg, Weibo, and Stack-Exchanges demonstrate significant gains (22% MAP@10) for Inf-VAE over state-of-the-art diffusion prediction models; we achieve massive gains for users with sparse activities, and users who lack direct social neighbors in seed sets.

DySAT: Deep Neural Representation Learning on Dynamic Graphs via Self-Attention Networks

Aravind Sankar, Yanhong Wu, Liang Gou, Wei Zhang, Hao Yang
Conference PaperInternational Conference on Web Search and Data Mining, WSDM 2020, Houston, TX, February 3-7, 2020


Learning node representations in graphs is important for many applications such as link prediction, node classification, and community detection. Existing graph representation learning methods primarily target static graphs while many real-world graphs evolve over time. Complex time-varying graph structures make it challenging to learn informative node representations over time. We present Dynamic Self-Attention Network (DySAT), a novel neural architecture that learns node representations to capture dynamic graph structural evolution. Specifically, DySAT computes node representations through joint self-attention along the two dimensions of structural neighborhood and temporal dynamics. Compared with state-of-the-art recurrent methods modeling graph evolution, dynamic self-attention is efficient, while achieving consistently superior performance. We conduct link prediction experiments on two graph types: communication networks and bipartite rating networks. Experimental results demonstrate significant performance gains for DySAT over several state-of-the-art graph embedding baselines, in both single and multi-step link prediction tasks. Furthermore, our ablation study validates the effectiveness of jointly modeling structural and temporal self-attention.

RASE: Relationship Aware Social Embedding

Aravind Sankar, Adit Krishnan, Zongjian He, Carl Yang
Conference PaperInternational Joint Conference on Neural Networks, IJCNN 2019 Budapest, Hungary, July 14-19, 2019


This paper studies the problem of learning latent representations or embeddings for users in social networks, by leveraging relationship semantics associated with each link. User embeddings are low-dimensional vector-space representations designed to preserve structural proximity indicated by the pairwise relationships. In social networks, the closeness (or proximity) between pairs of users is very different w.r.t. multiple social relationships and thus cannot be represented accurately using a single embedding space. Furthermore, social networks pose a unique challenge of relationship label sparsity that precludes the application of knowledge-graph embedding techniques.In this paper, we associate each observed link with multiple relationship types through relationship weights and learn projection matrices for each relationship type to model the social distance (or proximity) between users specific to each relationship. We propose a novel two-step mutual enhancement framework to iteratively (a) learn user embeddings preserving relationship-specific proximity, and (b) link-relationship weights capturing the role of each link in multiple relationship types. The first step learns user embeddings optimizing relationship-specific proximity, while fixing the relationship weights (or roles) for each link. In the second step, the user embeddings and corresponding projection matrices are assumed to be fixed, while the link-relationship weights are learned. We demonstrate that the relationship-aware user embeddings learned through this mutual enhancement framework, are more effective in representing the users and outperform representative baseline techniques in multi-label classification and relationship prediction tasks.

Meta-GNN: Metagraph Neural Network for Semi-supervised learning in Attributed Heterogeneous Information Networks

Aravind Sankar, Xinyang Zhang, Kevin Chang
Conference PaperIEEE/ACM 2019 International Conference on Advances in Social Networks Analysis and Mining, ASONAM 2019, Vancouver, Canada, August 27-30, 2019


Heterogeneous Information Networks (HINs) comprise nodes of different types inter-connected through diverse semantic relationships. In many real-world applications, nodes in information networks are often associated with additional attributes, resulting in Attributed HINs (or AHINs). In this paper, we study semi-supervised learning (SSL) on AHINs to classify nodes based on their structure, node types and attributes, given limited supervision. Recently, Graph Convolutional Networks (GCNs) have achieved impressive results in several graph-based SSL tasks. However, they operate on homogeneous networks, while being completely agnostic to the semantics of typed nodes and relationships in real-world HINs. In this paper, we seek to bridge the gap between semanticrich HINs and the neighborhood aggregation paradigm of graph neural networks, to generalize GCNs through metagraph semantics. We propose a novel metagraph convolution operation to extract features from local metagraph-structured neighborhoods, thus capturing semantic higher-order relationships in AHINs. Our proposed neural architecture Meta-GNN extracts features of diverse semantics by utilizing multiple metagraphs, and employs a novel metagraph-attention module to learn personalized metagraph preferences for each node. Our semi-supervised node classification experiments on multiple real-world AHIN datasets indicate significant performance gains of 6% Micro-F1 on average over state-of-the-art AHIN baselines. Visualizations on metagraph attention weights yield interpretable insights into their relative task-specific importance.

Discovering Maximal Motif Cliques in Large Heterogeneous Information Networks

Jiafeng Hu, Reynold Cheng, Kevin Chang, Aravind Sankar, Yixiang Fang, Brian Lam
Conference Paper35th IEEE International Conference on Data Engineering, ICDE 2019, Macao, China, April 8-11, 2019


We study the discovery of cliques (or "complete" subgraphs) in heterogeneous information networks (HINs). Existing clique-finding solutions often ignore the rich semantics of HINs. We propose motif clique, or m-clique, which redefines subgraph completeness with respect to a given motif. A motif, essentially a small subgraph pattern, is a fundamental building block of an HIN. The m-clique concept is general and allows us to analyse "complete" subgraphs in an HIN with respect to desired high-order connection patterns. We further investigate the maximal m-clique enumeration problem (MMCE), which finds all maximal m-cliques not contained in any other m-cliques. Because MMCE is NP-hard, developing an accurate and efficient solution for MMCE is not straightforward. We thus present the META algorithm, which employs advanced pruning strategies to effectively reduce the search space. We also design fast techniques to avoid generating duplicated maximal m-clique instances. Our extensive experiments on large real and synthetic HINs show that META is highly effective and efficient.

An Adversarial Approach to Improve Long-Tail Performance in Neural Collaborative Filtering

Adit Krishnan, Ashish Sharma, Aravind Sankar, Hari Sundaram
Conference PaperProceedings of the 27th ACM International Conference on Information and Knowledge Management, CIKM 2018, Torino, Italy, October 22-26, 2018


In recent times, deep neural networks have found success in Collaborative Filtering (CF) based recommendation tasks. By parametrizing latent factor interactions of users and items with neural architectures, they achieve significant gains in scalability and performance over matrix factorization. However, the long-tail phenomenon in recommender performance persists on the massive inventories of online media or retail platforms. Given the diversity of neural architectures and applications, there is a need to develop a generalizable and principled strategy to enhance long-tail item coverage. In this paper, we propose a novel adversarial training strategy to enhance long-tail recommendations for users with Neural CF (NCF) models. The adversary network learns the implicit association structure of entities in the feedback data while the NCF model is simultaneously trained to reproduce these associations and avoid the adversarial penalty, resulting in enhanced long-tail performance. Experimental results show that even without auxiliary data, adversarial training can boost long-tail recall of state-of-the-art NCF models by up to 25%, without trading-off overall performance. We evaluate our approach on two diverse platforms, content tag recommendation in Q&A forums and movie recommendation.

Unsupervised Concept Categorization and Extraction from Scientific Document Titles

Adit Krishnan, Aravind Sankar, Shi Zhi, Jiawei Han
Conference PaperProceedings of the 2017 ACM on Conference on Information and Knowledge Management, CIKM 2017, Singapore, November 06 - 10, 2017


This paper studies the automated categorization and extraction of scientific concepts from titles of scientific articles, in order to gain a deeper understanding of their key contributions and facilitate the construction of a generic academic knowledgebase. Towards this goal, we propose an unsupervised, domain-independent, and scalable two-phase algorithm to type and extract key concept mentions into aspects of interest (e.g., Techniques, Applications, etc.). In the first phase of our algorithm we proposePhraseType, a probabilistic generative model which exploits textual features and limited POS tags to broadly segment text snippets into aspect-typed phrases. We extend this model to simultaneously learn aspect-specific features and identify academic domains in multi-domain corpora, since the two tasks mutually enhance each other. In the second phase, we propose an approach based on adaptor grammars to extract fine grained concept mentions from the aspect-typed phrases without the need for any external resources or human effort, in a purely data-driven manner. We apply our technique to study literature from diverse scientific domains and show significant gains over state-of-the-art concept extraction techniques. We also present a qualitative analysis of the results obtained.

Predicting novel metabolic pathways through subgraph mining

Aravind Sankar, Sayan Ranu, Karthik Raman
Journal PaperBioinformatics


Motivation: The ability to predict pathways for biosynthesis of metabolites is very important in metabolic engineering. It is possible to mine the repertoire of biochemical transformations from reaction databases, and apply the knowledge to predict reactions to synthesize new molecules. However, this usually involves a careful understanding of the mechanism and the knowledge of the exact bonds being created and broken. There is a need for a method to rapidly predict reactions for synthesizing new molecules, which relies only on the structures of the molecules, without demanding additional information such as thermodynamics or hand-curated reactant mapping, which are often hard to obtain accurately. Results: We here describe a robust method based on subgraph mining, to predict a series of biochemical transformations, which can convert between two (even previously unseen) molecules. We first describe a reliable method based on subgraph edit distance to map reactants and products, using only their chemical structures. Having mapped reactants and products, we identify the reaction centre and its neighbourhood, the reaction signature, and store this in a reaction rule network. This novel representation enables us to rapidly predict pathways, even between previously unseen molecules. We demonstrate this ability by predicting pathways to molecules not present in the KEGG database. We also propose a heuristic that predominantly recovers natural biosynthetic pathways from amongst hundreds of possible alternatives, through a directed search of the reaction rule network, enabling us to provide a reliable ranking of the different pathways. Our approach scales well, even to databases with >100 000 reactions. Supplementary information: Supplementary data are available at Bioinformatics online.

Improved MHP Analysis

Aravind Sankar, Soham Chakraborty, V. Nandivada
Conference PaperProceedings of the 25th International Conference on Compiler Construction, CC 2016, Barcelona, Spain, March 12-18, 2016


May-Happen-in-Parallel (MHP) analysis is becoming the backbone of many of the parallel analyses and optimizations. In this paper, we present new approaches to do MHP analysis for X10-like languages that support async-finish-atomic parallelism. We present a fast incremental MHP algorithm to derive all the statements that may run in parallel with a given statement. We also extend the MHP algorithm of Agarwal et al.(answers if two given X10 statements may run in parallel, and under what condition) to improve the computational complexity, without compromising on the precision.

Similarity Learning for Product Recommendation and Scoring Using Multi-channel Data

Iftikhar Burhanuddin, Payal Bajaj, Sumit Shekhar, Dipayan Mukherjee, Ashish Raj, Aravind Sankar
Workshop PaperIEEE International Conference on Data Mining Workshop, ICDMW 2015, Atlantic City, NJ, USA, November 14-17, 2015


Customers may interact with a retail store through many channels. Technology now makes it is possible to track customer behavior across channels. We propose a system where items are recommended based on learning channel specific similarities between customers and items. This is done by treating recommendations as a learning to rank problem and minimizing rank loss with surrogate loss functions. We build our system using a real world multi-channel data set -- online browse and purchase, and in-store purchase -- from a retail chain. The results show that using learned similarity scores improves the performance of the system over scores generated using standard cosine similarity measures. Finally, using our learning to rank formulation we introduce a product scoring system to measure consumption behavior.