Jump To Hyperspace: Comparing Euclidean and Hyperbolic Loss Functions for Hierarchical Multi-Label Text Classification

Abstract

Hierarchical Multi-Label Text Classification (HMTC) is a challenging machine learning task where multiple labels from a hierarchically organized label set are assigned to a single text. In this study, we examine the effectiveness of Euclidean and hyperbolic loss functions to improve the performance of BERT models on HMTC, which very few previous studies have adopted. We critically evaluate label-aware losses as well as contrastive losses in the Euclidean and hyperbolic space, demonstrating that hyperbolic loss functions perform comparably with non-hyperbolic loss functions on four commonly used HMTC datasets in most scenarios. While hyperbolic label-aware losses perform the best on low-level labels, the overall consistency and micro-averaged performance is compromised. Additionally, we find that our contrastive losses are less effective for HMTC when deployed in the hyperbolic space than non-hyperbolic counterparts. Our research highlights that with the right metrics and training objectives, hyperbolic space does not provide any additional benefits compared to Euclidean space for HMTC, thereby prompting a reevaluation of how different geometric spaces are used in other AI applications.