CLC-RS: A Chinese Legal Case Retrieval System with Masked Language Ranking

Abstract

With the ever-increasing size of legal cases in China, relevant legal case retrieval given a user query has attracted considerable attention. Conventional keyword-based retrieval systems look for matching cases that contain one or more words specified by the user. However, keyword search is sharply focused on finding the exact terms specified in the query, making the retrieval systems miss many relevant documents. In addition, it is difficult for new users to identify appropriate keywords for accurate legal case retrieval. In this paper, we develop a novel Chinese legal case retrieval system (called CLC-RS), which improves the quality of semantic search with natural language queries in the legal domain. CLC-RS performs legal case retrieval in a two-stage fashion. First, we employ a classic token-based ranking method to efficiently reduce the solution space, returning a subset of candidate legal cases. Then, we deploy a novel masked language ranking model to re-rank the candidate legal cases. The experimental results show that the proposed system is both efficient and effective, providing a practical information retrieval (IR) system for retrieving Chinese legal cases. The web site for the developed CLC-RS system is available at: https://www.delilegal.com/.