Formalization of terminological ontologies

The applicability of thesauri in the classification and information retrieval context has promoted the creation and diffusion of well-established thesauri in many different domains. These simple models are useful for most of classification and retrieval systems where search requisites are not very elaborated; however, in contexts with an information model of great complexity, more elaborated ontologies with formal is-a hierarchies, frame definitions or even general logical constraints are needed to improve the retrieval quality.