Nowadays, a central topic in database science is the need of an integrated access to large amounts of data provided by various information sources whose contents are strictly related. Often information sources have been designed independently for autonomous applications, so they may present several kinds of heterogeneity. Particularly hard to manage is the semantic heterogeneity, which is due to schema and value inconsistencies. In this paper, we focus our attention mainly on the inconsistency which arises when conflicting instances related to the same concept and possibly coming from different sources are integrated. First, we