Towards a Framework for Legal Case Retrieval
Authors: Tebo Leburu-Dingalo
Venue: SIGIR
Year: 2024

Legal case reports detail the main points of a decided case, findings and decisions of the court. The reports are a fundamental source for Case law, a law which requires judges to align their rulings with previous judicial decisions on similar cases [1]. Timely and reliable access to case reports is thus of critical importance to legal practitioners working on a current case, and laymen interested in the outcome of cases. However, ensuring effective retrieval of previous case reports is still proving a challenge, even with the use of retrieval technologies already proven effective in other Information Retrieval (IR) domains. This has been attributed to factors such as lack of structure, and lengthiness of case report documents, and queries formulated to represent an ongoing case for which the reports are being sought [4]. To address these factors we propose an IR framework that focuses on infusing structure into the documents and queries through the identification of legal rhetorical roles such as arguments and facts in the text. Furthermore, we aim to explore the use of selected groupings of these rhetorical roles as representations for the documents and queries. The benefit of using selected content is illustrated in recent research where for instance segments of documents such as abstracts, case headers, specific paragraphs, and sentences have been used to build effective legal IR systems. We thus hypothesize that we can attain marked improved performance when we build a case retrieval system using only a section of a case report or a query such as arguments or facts. However, in contrast to these studies we posit that utilizing rhetorical role information to extract content will lead to more effective representations that can enhance the performance of case retrieval systems. The proposed framework will consists of a set of components needed to process both query and case report text to firstly infuse structure, extract effective representative content and finally perform retrieval. To aid the development of the framework, several empirical investigations will be conducted on publicly accessible datasets, and a self-curated test collection derived from Botswana legal case reports. Key research questions to assist in our investigation are as follows: : Can we successfully detect the implicit elements of a legal text reflecting rhetorical roles significant to legal case documents? RQ2: In comparison to human formulated queries, do whole case queries give better performance? RQ3: Can we improve retrieval performance by only retaining textual units representing specific rhetorical roles from an entire query text (current case)? RQ4: Does indexing only textual units representing specific rhetorical roles from prior case documents improve retrieval performance? RQ5: Do the selected approaches result in performance improvement for our local corpus in terms of precision, recall and user satisfaction? Some preliminary work has been done and published towards investigating the viability of using summaries in legal case retrieval and identification of rhetorical roles in case documents. We submitted results of a system that utilized expanded summarized queries for an AILA precedent retrieval task competition that outperformed other submissions [2]. Furthermore, our approach that utilized TagCrowd for summarization performed well on a task of Statute retrieval [5]. Towards the feasibility of rhetorically labelling legal text we experimented with the fastText classifier for an AILA organized task. While our methods did not attain state-of-the-art, they gave insights into the performance of the different roles and factors that can affect performance in the task. [3].