Understanding data semantics from existing relational databases is important for several applications such as database maintenance and analysis, database re-engeenering or query optimization. Data semantics is carried out in particular by integrity constraints. For most operational databases, particularly for the oldest ones, we cannot assume to dispose of this knowledge. In this paper, we present a tool called DBA Companion which can be an help to deal with the understanding of existing relational databases. This tool integrates algorithms to deal with the extraction of integrity constraints and several related problems. From this mined knowledge, the logical tuning of databases can be achieved.