We explore how an ontology may be used with a database to support reasoning about the “information content” of data whereby to reveal hidden information that would otherwise not derivable by using conventional database query languages. Our basic ideas rest with “ontology” and the notions of “information content”. A public ontology, if available, would be the best choice for reliable domain knowledge. To enable an ontology to work with a database would involve, among others, certain mechanism thereby the two systems can form a coherent whole. This is achieved by means of the notion of “information content inclusion relation”, IIR for short. We present what an IIR is, and how IIR can be identified from both an ontology and a database, and then reasoning about them.