Online querying relational data based on closure

Semantic Web has promoted researches on semantic integration of heterogeneous relational databases. Ontology-based heterogeneous relational data integration is recently attracting many diverse attentions, since most of the information is still stored in relational databases. This paper focuses on the query efficiency problem of ontology-based heterogeneous relational databases querying. To improve the query efficiency, we presented an approach for semanticbased querying of relational data. Global schema is described in RDF(S) and can be abstracted as graph. SPARQL queries over global schema are executed by graph mapping. Rounder graph of global schema is generated offline by calculating the RDFS closure of the schema. Our approach has decreased time cost of online querying and improved the efficiency.