The French institute INA is interested in ontologies in order to describe the content of audiovisual documents. Methodologies and tools for building such objects exist, but few propose complete guidelines to help the user to organize the key components of ontologies: subsumption hierarchies. This article proposes to use a methodology introducing a clear semantic commitment to normalize the meaning of the concepts. We have implemented this methodology in an editor, DOE, complementary to other existing tools, and used it to develop several ontologies.