Cultural-heritage collections are typically indexed with metadata derived from a range of different vocabularies, such as AAT, Iconclass and in-house standards. This presents a problem when one wants to use multiple collections in an interoperable way. In general, it is unrealistic to assume unification of vocabularies. Vocabularies have been developed in many sub-domains, each with their own emphasis and scope. Still, there is significant overlap between the vocabularies used for indexing. The prime research objective of this subproject is to develop theory, methods and tools for allowing metadata interoperability through semantic links between the vocabularies. This research challenge is similar to what is called the “ontology mapping” problem in Semantic Web research.