between Vocabulary Heterogeneity and Loss of Information Eduardo Mena Facultad de Inform atica UPV/EHU San Sebasti an. Spain email@example.com Vipul Kashyap LSDIS Lab, UGA & CS dept., Rutgers Univ. New Brunswick, NJ 08903 firstname.lastname@example.org Arantza Illarramendi Facultad de Inform atica UPV/EHU San Sebasti an. Spain email@example.com Amit Sheth LSDIS Lab http://lsdis.cs.uga.edu/ UGA, Athens, GA 30602 firstname.lastname@example.org Abstract. The ability to deal with a huge number of independent and heterogeneous repositories is the most critical problem in Global Information Systems. One approach to enable e cient query processing is by utilizing semantic descriptions (organized as ontologies) of such repositories whenever available. In this context semantic relationships among ontologies can be used by Query Processors. Three kind of relationships are considered: synonyms, hyponyms and hypernyms. Using synonyms the semantics of the query is preserved; however, when synonyms are not available and hypernyms or hyponyms are used there exists some loss of information that must be measured.