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Ontology-Based Knowledge Graph Approach for Legal Queries
Pub. online: 5 January 2026      Type: Research Article      Open accessOpen Access
Received
1 October 2024
Accepted
1 December 2025
Published
5 January 2026

Abstract

In the legal domain, ontologies organize legal concepts and their relationships, while knowledge graphs connect these concepts to specific entities in legal documents. This study proposes a solution for integrating ontology and knowledge graph, called Legal-Onto model, to construct a knowledge base of an intelligent retrieval system in the legal domain. The Legal-Onto model combines ontology as the conceptual layer and knowledge graphs as the implementation layer for representing the content of legal documents. This relational model is integrated with a structure of knowledge graph to identify relations between concepts and entities extracted from ontology in the determined domain. Moreover, this research addresses inherent challenges in semantic-based knowledge-driven search. The specific objective is to accurately extract relevant information from legal documents to respond to entered queries. The experimental results show that this method is more effective than state-of-the-art methods in natural language processing and large language models, which are without specific legal domain knowledge.

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Biographies

Pham Vuong T.
vuong.pham@sgu.edu.vn

V.T. Pham received the BS degree in mathematics and informatics from the University of Science, VNU-HCM, Vietnam, in 2003, and the MS degree in Information Technology from University of Science, VNU-HCM, Vietnam, in 2008. He is currently a PhD student at University of Science, VNU-HCM. He is also a lecturer at Sai Gon University, Vietnam. From 2006–2019, he was a lecturer at the Faculty of Software Engineering, University of Information Technology, VNU-HCM, Vietnam. His research interests include artificial intelligence, computer science, software engineering, mathematics foundation.

Dung Dang V.
dungdv@uit.edu.vn

D.V. Dang received his MSc degree in computer science in 2023. He is currently a PhD candidate in the Department of Computer Science since 2025 and serves as a lecturer at the Faculty of Software Engineering, University of Information Technology, Vietnam National University Ho Chi Minh City, Vietnam. His research interests include knowledge representation, automated reasoning, and knowledge engineering.

Ngo Hung Q.
hung.ngo@ucd.ie

Hung Q. Ngo is a PostDoc Researcher at the School of Computer Science, University College Dublin (UCD), Ireland. He received his PhD degree in computer science from the University College Dublin in 2022 and his MSc degree in computer science from the University of Science, Vietnam National University – Ho Chi Minh City (VNUHCM), Vietnam in 2008. His research interests include knowledge management, natural language processing, and intelligent systems in cross-disciplinary domains, such as bioinformatics, digital agriculture, legal AI, and digital forensics.

Nguyen Binh
ngtbinh@hcmus.edu.vn

B.T. Nguyen received the PhD degree (Hons.) from Ecole Polytechnique, Paris, France, in 2012. He is currently the head of the Department of Computer Science and an associate professor of Computer Science with the Faculty of Mathematics and Computer Science, University of Science, Vietnam National University Ho Chi Minh City, Ho Chi Minh City, Vietnam. He has over ten years of experience in AI and data science. Up to now, he has had over 100 publications and 04 patents filed in USA and Canada. He has substantial experience building research and development teams to help companies or startups deliver AI products.

Do Nhon V.
nhondv@hiu.vn

N.V. Do received his MSc and PhD degrees in computer science from University of Science, VNU-HCM, Vietnam in 1995 and 2002, respectively. He was an Associate Professor at University of Information Technology, VNU-HCM, Vietnam, from 2006 to 2018 and at Hoa Sen University, Vietnam, from 2018 to 2019. He has been an associate professor and the head of Information Technology Department at Hong Bang International University, Vietnam, from 2020. His research interests include artificial intelligence, computer science, and their practical applications, especially intelligent systems and knowledge-based systems.

Selamat Ali
aselamat@utm.my

A. Selamat is currently a full professor with Universiti Teknologi Malaysia (UTM), Malaysia. He is a Deputy Vice Chancellor (Student Affairs & Alumni), UTM. He was the Dean of the Malaysia Japan International Institute of Technology (MJIIT), UTM, since 2018. He is also a Professor with the Software Engineering Department, Faculty of Computing, UTM, and was the Chair of the IEEE Computer Society Malaysia Section. He has published more than 120 research articles with IF JCR, with more than 2400 citations received in the Web of Science. His research interests include software engineering, software agents, web engineering, information retrievals, pattern recognition, genetic algorithms, neural networks, soft computing, collective computational intelligence, strategic management, key performance indicator, and knowledge management.

Nguyen Hien D.
https://orcid.org/0000-0002-8527-0602
hiennd@uit.edu.vn

H.D. Nguyen is currently an associate professor at the Faculty of Computer Science, University of Information Technology, VNU-HCM, Vietnam, from 2008. He was a Visiting Assistant Professor at the Computer Science Department, New Mexico State University (NMSU), USA, in 2024–2025. His research interests include knowledge representation, automated reasoning, and knowledge engineering, especially intelligent systems in education, such as intelligent problem solvers. He received the Best Paper Awards at CITA 2023, SOMET 2022, and ICOCO 2022.


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Keywords
knowledge-based systems knowledge graph legal domain information retrieval knowledge representation

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