This chapter discuss an application from medical information science more specifically, the NCI Thesaurus. author will first discuss some ontological shortcomings of the representation of social entities in this thesaurus in the next section, below, and will then suggest four rules for classifying social entities. To confirm this relevance, author will draw on real-world examples from the National Cancer Institute Thesaurus (NCIT), a terminology database designed especially for the needs of the US National Cancer Institute (NCI). Thus the social entities are concerned, the NCIT is far from meeting these objectives and, second, that the currently emerging philosophical discipline of social ontology can come to its aid. Moreover. The aim of this essay was to show how social ontology can help to classify social entities in medical information sciences. Using the current research in social ontology as background, It presents four rules for the classification of social entities and applied them to examples from the NCIT.