OntRel: An Ontology Indexer to Store OWL-DL Ontologies and Its Instances

Ontology is one of the most important components of a semantic based information system which provides context to the document. Ontology enables us to capture the semantics of documents. To interpret information and perform reasoning we require storing ontologies in a way that is correct, consistent, scalable and efficient to retrieve. RDBMS (relational database management systems) is the most efficient and reliable data structure in terms of storage and retrieval. One of the ways is to store ontologies in RDBMS. OWL is used to represent ontologies. To store OWL documents in RDBMS multiple techniques have been proposed, but they either deal with single ontology or they do not store complete semantics expressed in OWL ontologies which compromise the correct retrieval of the data. Some of the techniques are not really scalable, as the ontology is dynamic and extensible where as the RDBMS schema is not dynamically extensible. So, there is a need to preserve the dynamic OWL documents in the Relational structure in such a way that no data or relationship is lost and advantages of RDBMS are also gained. This paper addresses the issue of storing multiple OWL ontologies in an RDBMS in a way that is correct, consistent, scalable and efficient to retrieve. A relational schema, with the name of OntRel, has been proposed along with a set of rules to populate database from OWL documents. OntRel has been implemented and tested and available as on the web for open use. Finally, we have compared the Load time, Query performance and completeness of OntRel with other indexing techniques using Lehigh University Benchmark (LUBM) and University Ontology Benchmark (UOBM).