The recent Web generation called Semantic Web provides a framework allowing a semantic description based on ontology for the web resources. OWL (Web Ontology Language), specifically designed for this framework, is widely used as a formal language for ontology formulation. With OWL, we can describe not only ontologies of different resources but also their correspondences. In this research work, we focus on the transition from data sources to Semantic Web, in particular the relational databases which are major data sources. We develop a proper tool for extracting an OWL ontology from a relational database. This tool, also known as wrapper, generates an OWL ontology from a database and allows the user to query the databases in terms of ontology. The translation of relational schema to OWL ontology follows some transformation rules. The specific rules can be defined by the user in order to get a particular ontology.