The volume and variety of data published on the Semantic Web is constantly increasing with a growing number of entities and stakeholders expressing their data in the form of OWL and/or RDFS ontologies. However, a large amount of data is still maintained in relational databases. The recent developments in SPARQL endpoints, such as D2R server, constitute an important step towards the introduction of relational databases in the Semantic Web. However, the underlying models are tightly linked with the data structure and controlled terminologies employed, and hence, they pose a serious barrier to accessing the data by using different languages. In our previous work, we presented an Ontology Alignment Tool for bridging the gap among the terms of two ontologies based on the instantiation of one or more Ontology Patterns. In this paper, we analytically describe a novel approach and an accordingly designed system for enabling users to access data residing in relational databases by using different models and vocabularies than the ones supported by the SPARQL endpoint. The approach is based on the specification and consumption of correspondences with particular focus on SPARQL query and RDF data rewriting mechanisms, which are responsible for making the necessary changes in the queries and optionally results retrieved from the SPARQL endpoint taking into account the models and vocabularies used in each side.