The paper presents the COGITO system, an automated classification system realized for the Library of the Italian Chamber of Deputies compliant with the EuroVoc thesaurus. COGITO supports the cataloguing and classification of parliamentary and legislative documents; each document is analyzed and interpreted in order to then be archived quickly in the corresponding category, after a validation by a human operator. The history of this categorization project is briefly reported together with the analysis of both TESEO and EuroVoc thesauri. The semantic technology utilized in the automatic classification is largely explained with a specific focus on the semantic possibility of disambiguation.