Semantic Web applications often rely on the reuse of underlying data from legacy information systems. The motivation for our research is how to make this data accessible for use in such applications. We propose the use of ontologies and conceptual modelling in an overall approach for data interoperability. The approach incorporates a process for ontology alignment using our tool for visual ontology alignment. First results from our tool evaluation were promising and show that visualization is useful for locating additional candidate alignments by an end user.