LeCoPCR: Legal Concept-guided Prior Case Retrieval for European Court of Human Rights cases

TL;DR

LeCoPCR improves legal case retrieval by explicitly generating and incorporating legal concepts from query cases, enhancing relevance understanding through weak supervision and key concept extraction, leading to better retrieval performance.

Contribution

This work introduces LeCoPCR, a novel method that explicitly generates legal concepts from case facts and uses DPP for key concept extraction, improving prior case retrieval accuracy.

Findings

Effective legal concept generation enhances retrieval relevance

DPP-based key concept extraction improves quality and diversity

Experimental results show improved performance on ECtHR-PCR dataset

Abstract

Prior case retrieval (PCR) is crucial for legal practitioners to find relevant precedent cases given the facts of a query case. Existing approaches often overlook the underlying semantic intent in determining relevance with respect to the query case. In this work, we propose LeCoPCR, a novel approach that explicitly generate intents in the form of legal concepts from a given query case facts and then augments the query with these concepts to enhance models understanding of semantic intent that dictates relavance. To overcome the unavailability of annotated legal concepts, we employ a weak supervision approach to extract key legal concepts from the reasoning section using Determinantal Point Process (DPP) to balance quality and diversity. Experimental results on the ECtHR-PCR dataset demonstrate the effectiveness of leveraging legal concepts and DPP-based key concept extraction.