Title: SemSup-XC: Semantic Supervision for Extreme Classification. Abstract: Extreme classification (XC) considers the scenario of predicting over a very large number of classes (thousands to millions), with real-world applications including serving search engine results, e-commerce product tagging, and news article  classification. The zero-shot version of this task involves the addition of new categories at test time, requiring models to generalize to novel classes without
additional training data (e.g. one may add a new class “fidget spinner” for ecommerce product tagging). In this paper, we develop SEMSUP-XC, a model that achieves state-of-the-art zero-shot (ZS) and few-shot (FS) performance on three extreme classification benchmarks spanning the domains of law, e-commerce, and Wikipedia. SEMSUP-XC builds upon the recently proposed framework of semantic supervision that uses semantic label descriptions to represent and generalize to classes (e.g., “fidget spinner” described as “A popular spinning toy intended as a stress reliever”). Specifically, we use a combination of contrastive learning, a hybrid lexico-semantic similarity module and automated description collection to train SEMSUP-XC efficiently over extremely large class spaces. SEMSUP-XC
significantly outperforms baselines and state-of-the-art models on all three datasets, by up to 6-10 precision@1 points on zero-shot classification and >10 precision points on few-shot classification, with similar gains for recall@10 (3 for zero-shot and 2 for few-shot). Our ablation studies and qualitative analyses demonstrate the relative importance of our various improvements and show that SEMSUP-XC’s
automated pipeline offers a consistently efficient method for extreme classification.