In this paper we show how semantic web technologies are used in a real application in the domain of national medical databases where an important technological gap between the legacy relation databases and OWL ontologies is bridged by the recently standardized UML profile for OWL. After data has been exported from multiple relational databases into a single shared RDF database structured according to an integrated OWL ontology there emerges a need for a convenient end-user query tools. We describe a fully graphical access to the exported data through the graphical front-end tool (named “DEMO” tool) based on the UML profile for OWL and SPARQL query language.