Abstract. The definition of a domain ontology is a complex activity that requires two kinds of expertise: a deep knowledge of the domain to be modeled and a good level of familiarity with the ontology representation language to be used in order to formalize the built model. Existing ontology languages (such as SHOE, DAML+OIL, OWL) are inherently general purpose, allowing different domains to be tackled and modeled. We believe it is possible to enrich an ontology language with domain specific features to ease the ontology building process. Such a goal can be achieved along two lines. One is to provide a core domain ontology, containing the most general concepts in the domain of interest; another is to introduce specific modeling constructs in the ontology language. The latter option, referred to as domain adequacy, is addressed in this paper. We will show that adding a few domain specific concept categories in the language allows better ontologies to be built. Keywords. ontology languag...