The Semantic Web aims at easy integration and usage of content by building on a semi-structured data model where data semantics are explicitly specified through ontologies. The use of ontologies in real-world applications such as community portals has shown that a new level of data independence is required for ontology-based applications for example to allow the customization of information towards the needs of other agents. This requires control over the republishing of data and requires transformation of data across source databases. We address this issue and introduce external ontologies which are constituted of source data from several databases and views spanning across databases.