We present a RDB2OWL mapping specification language that is aimed at presenting RDB-to-RDF/OWL mappings possibly involving advanced correspondences between the database and ontology in a human comprehensible way. The RDB2OWL mappings can be regarded as documentation of the database-to-ontology relation. The RDB2OWL language reuses the OWL ontology structure as a backbone for mapping specification by placing the database link information into the annotations for ontology classes and properties. It features reuse of database table key information, user defined and table functions, as well as multiclass conceptualization that is essential for keeping the mapping compact in case of creating a conceptual partitioning of large database tables. We report also on initial implementation experience for a subset of RDB2OWL constructs.