An onthology represents an important resource for the organisation of a domain's knowledge in a more detailed way by explicating all possible semantic relations existing between the various concepts. Starting from the terminology selection already used for thesaurus generation, the following onthology systematisation makes more specific the relations among the thesaurus elements. Thus, in the onthology the concepts related to a dominion defined through classes are related in a definitive and unambiguous way, so to optimize the process semantic disambiguation for knowledge representation. Each class might have sub-categories inheriting its relations with other classes from the desired description and representation domain.