BERT-TSR: A BERT-based two-stage ranking model for legal case retrieval
摘要
Effective legal case retrieval is critical for fair and just adjudication of similar cases. Unfortunately, current methods fall short of understanding legal cases at a semantic level. To address the issue, this paper presents a BERT-based two-stage ranking model for Chinese legal case retrieval. The first stage uses the well-known BM25 ranking function to quickly retrieve top n case candidates from the candidate pool. In the second stage, firstly the fine-tuned BERT is used for semantic analysis of the retrieved case candidates (i.e., obtained their embeddings) and then a ranking mechanism is used to re-rank the retrieved cases. We fine-tune the BERT model by integrating the point-wise method with auxiliary learning to better understand the deep semantics of a legal judgement text, and we further train the re-ranking neural network based on the fine-tuned BERT model in conjunction with the pair-wise method. Our extensive experiments reveal that the proposed method surpasses state-of-the-art methods on the Legal Case Retrieval Dataset (LeCaRD) by improving the ranking quality of retrieved legal cases, leading to more relevant cases appearing higher in the ranked results.