The ability to share and combine geographic data from different information sources in a consistent way is a key issue for enabling successful implementation of Spatial Data Infrastructures. This can only be done through a deep understanding of databases structure and content. In this paper, we propose to do that through the elicitation and formalisation of geographic database specifications, relying on OWL ontologies, as recommended in the semantic Web community. We thus propose a general ontology for eliciting key concepts manipulated by data specifications, and rules to build local ontologies representing knowledge contained in specific data specifications.