This topic is dedicated to the challenges of model based interoperability and related issues, The principles of interoperability are included in DA3-2. In detail: - The challenges of model interoparability (semantics, different modelling of the same features in different models, syntacs) - Overview on IT concepts for schema integration / transformation - Approaches for model integration - Approaches for model transformations, e.g. related to INSPIRE, from the Humboldt project