An Approach for Mapping Relational Database into Ontology Mohamed A.G. Hazber 1 , Ruixuan Li 1 , Yuxi Zhang 2 , Guandong Xu 3 1. School of Computer Science and Technology Huazhong University of Science and Technology Wuhan, China moh_hazbar@yahoo.co.uk, rxli@hust.edu.cn 2. Department of Electronics and Information Engineering Huazhong University of Science and Technology Wuhan, China 624374923zyx@gmail.com 3. Faculty of Engineering & IT University of Technology Sydney Sydney, Australia guandong.xu@uts.edu.au Abstract—Sharing and reusing the big data in relational databases in a semantic way have become a big challenge. In this paper, we propose a new approach to enable semantic web applications to access relational databases (RDBs) and their contents by semantic methods. Domain ontologies can be used to formulate RDB schema and data in order to simplify the mapping of the underlying data sources. Our method consists of two main phases: building ontology from an RDB schema and the generation of ontology instances from an RDB data automatically. In the first phase, we studied different cases of RDB schema to be mapped into ontology represented in RDF(S)- OWL, while in the second phase, the mapping rules are used to transform RDB data to ontological instances represented in RDF triples. Our approach is demonstrated with examples and validated by ontology validator. Keywords—Relational database; Semantic web ontology; RDF(S); OWL; Mapping rule I. INTRODUCTION The continuous explosion of RDF (resource description framework) data opens door for new innovations in big data and semantic web initiatives, which can be shared and reused through application, enterprise and community boundaries. The World Wide Web Consortium (W3C) has recommended several formats for representing web ontology, such as RDF [1] data model, which is a standard model for data interchange on the web, RDF Schema [2], provides a data-modeling vocabulary for RDF data, and web ontology language (OWL) [3] as a formal language for authoring ontologies. The bulk of existing web content is stored in RDBs [4], which characterized by high quality of storing and querying data but lack the ability to describe the semantics of data. In order to utilize today’s RDB to support web applications and transparently participate in the semantic web, their associated database schemas need to be converted into semantically equivalent ontologies. Mapping RDB to RDF/OWL is an attractive field of research and many approaches have been proposed. Most of these approaches are simple, equivalent matching and neglecting the formal definition which may lead to ambiguous when applying several transformation rules [5- 8]. Through these approaches there are still difficulties for domain expert to understand the meaning between these approaches, such as unclear generation approach, un-unified ontology language and other related problems. Since, the manual ontology construction is a complex, cumbersome, mistakable, time consuming, high cost process, and requires the supports of domain experts in knowledge acquisition, the main goal of our approach is to generate ontology automatically from RDB and covers all possible concepts of relational model to find their best transformation into the ontology model. The major contributions of this paper are as follows. (1) We propose a new approach for direct mapping RDB to ontology automatically containing: (a) Twenty-five unambiguous and well defined sequential mapping rules, and (b) Two well-defined functions identifying binary relations and generating identifier RowId. (2) The transformation rules are designed in an obvious form, so that the rules can be extended to reverse ontology to relational tables. (3) We design architecture that provides a uniform semantics between ontology mapping and information integration. The rest of this paper is organized as follows. Section 2 discusses the related work. Section 3 shows our proposed architecture and the rules for mapping RDB (schema and data) into semantic web ontology (schema and instance). The comparison is presented in Section 4. Finally, Section 5 concludes this paper with the future work. II. RELATED WORK Different researches have been established in this area to provide methods and tools that exposed or converted data in RDB as ontological data described in RDF. The W3C RDB2RDF Incubator Group [9] has formed a working group to create a standard for exposing RDB as RDF. Ontology has been extracted from RDB by two ways automatic [10, 11] and semi-automatic [6, 12, 13, 14]. An approach presented by [10] This work is sponsored by National Natural Science Foundation of China under grants 61173170, 61300222, 61433006 and U1401258, and Innovation Fund of Huazhong University of Science and Technology under grants 2015TS069 and 2013QN120, and Science and Technology Support Program of Hubei Province under grant 2014BCH270.