However much the various top-level categories may assume different values in the different levels of the ontology, they must nevertheless have something in common. Although 'part-of' differs as regards inanimate and animate objects, in both cases we always speak of 'parts' and distinguish 'parts' from the other categories. Categorial ontology studies the various ways in which a category is realized in the diverse ontological levels, ascertaining the possible presence of a general theory which subsumes its various concretizations. While general ontology is more concerned with the architectonic of the theory, regional ontology is more sensitive to the details of the individual categories. Both of them, however, are obviously necessary.
Generic ontologies seem peculiarly tied to conceptual lexica and linguistic corpora.
In fact, terms can be categorized at several levels. On the other hand, domain ontology contains terms which do not have analytical correspondences in generic ontologies. Knowledge of the domain 'fills' or 'saturates' generic knowledge. We know that each ontological level is characterized by the presence of a group of categories typical of that level. The first task, therefore, is to find the most general categories typical of that level.