Large Language Model based Long-tail Query Rewriting in Taobao Search

In the realm of e-commerce search, the significance of semantic matching cannot be overstated, as it directly impacts both user experience and company revenue. Query rewriting serves as an important technique to bridge semantic gaps inherent in the semantic matching process. However, existing query rewriting methods often struggle to effectively optimize long-tail queries and alleviate the phenomenon of \textit{``\nothing''} caused by semantic gap. In this paper, we present \textbf{\method}, a comprehensive framework that \textbf{B}ridges the s\textbf{E}mantic gap for long-tail \textbf{QUE}ries. \method comprises three stages: multi-instruction supervised fine tuning (SFT), offline feedback, and objective alignment. Specifically, we first construct a rewriting dataset based on rejection sampling, and mix it with multiple auxiliary tasks data to fine tune our large language model (LLM) in a supervised fashion during the first stage. Subsequently, with the well-trained LLM, we employ beam search to generate multiple candidate rewrites, which would be fed into Taobao offline system to simulate the retrieval process and obtain the partial order. Leveraging the partial order of candidate rewrites, we introduce a contrastive learning method to highlight the distinctions between rewrites and align the model with the Taobao online objectives. Offline experiments prove the effectiveness of our method in enhancing retrieval performance. Online A/B tests reveal that our method can significantly boost gross merchandise volume (GMV), number of transaction (\#Trans) and unique visitor (UV) for long-tail queries. \method has been deployed on Taobao, one of most popular online shopping platforms in China, since October 2023.