Optimizing Tail-Head Trade-off for Extreme Multi-Label Text Classification (XMTC) with RAG-Labels and a Dynamic Two-Stage Retrieval and Fusion Pipeline

We tackle Extreme Multi-Label Text Classification (XMTC), which involves assigning relevant labels to texts from a huge label space. Attempting to optimize the underexplored tail-head trade-off, we address the XMTC task through its core challenges of volume, skewness, and quality by proposing xCoRetriev, a novel two-stage retrieving and fusing ranking pipeline. Our pipeline addresses the volume challenge by dynamically slicing the large label space; it also tackles the skewness challenge by favoring the tail labels while fusing sparse and dense retrievers. Finally, xCoRetriev faces the quality challenge by enhancing the label space with Retrieval-Augmented Generated (RAG)-labels. Our experiments with four XMTC benchmarks with hundreds of thousands of text documents and labels against six state-of-the-art XMTC baselines demonstrate xCoRetriev's strengths in terms of: (i)~scalability for large label spaces, being among the most efficient methods at training and prediction; (ii)~effectiveness in the face of high skewness, with gains of up to 48% in propensity-scored metrics against the best state-of-the-art baselines; and (iii)~capability of handling very noisy datasets by exploiting RAG-labels.