In this paper we present propositions which we have argued elsewhere concerning ontology and data models. Additionally, we present evidence relating to our propositions. We have found that Chisholm’s ontology has the potential to be a unifying theory for data models. In addition, our research has lead us to the position that ontologies founded in the philosophical tradition of realism seem to serve the purpose of a unifying framework for data models. Further, we have seen the realistic ontologies by Mario Bunge and Roderick Chisholm used in information systems. We believe that realistic ontologies have a role to play in understanding information systems.