Abstract. The wide use of a number of cultural heritage metadata schemas imposes the development of new interoperability techniques that facilitate unified access to cultural resources. In this paper, we focus on the ontology based semantic integration by proposing an expressive mapping language for the specification of the mappings between the XML-based metadata schemas and the CIDOC CRM ontology. We also present an algorithm for the transformation of XPath queries posed on XML-based metadata into equivalent queries on the CIDOC CRM ontology.