DiAL: Diversity aware listwise ranking for query auto-complete

Query Auto-Complete (QAC) is an essential search feature that suggests users with a list of potential search keyword completions as they type, enabling them to complete their queries faster. While the QAC systems in eCommerce stores generally use the Learning to Rank (LTR) approach optimized based on customer feedback, it struggles to provide diverse suggestions, leading to repetitive queries and limited navigational suggestions related to product categories, attributes, and brands. This paper proposes a novel DiAL framework that explicitly optimizes for diversity alongside customer feedback signals. It achieves this by leveraging a smooth approximation of the diversity-based metric (αNDCG) as a listwise loss function and modifying it to balance relevance and diversity. The proposed approach yield an improvement of 8.5% in mean reciprocal rank (MRR) and 22.8% in αNDCG compared to the pairwise ranking approach on an eCommerce dataset, while meeting the ultra-low latency constraints of real time QAC systems. In an online experiment, the diversity-aware listwise QAC model resulted in a 0.48% lift in revenue. Furthermore, we replicated the proposed approach on a publicly available search log, demonstrating improvements in both diversity and relevance of the suggested queries.