Query by diagram: a graphical environment for querying databases

Recently proposed visual systems which allow a user to extract information by means of interactive graphical commands, have not yet been able to combine ease of use and high expressive power. The QBD* (Query By Diagram) system tries to overcome the above limitations. It balances a high expressive power with a noticeable facility of use. A systematic study has been performed to establish the effectiveness of the QBD* environment. The study involved 90 non experts in computer science (undergraduate students, employees, and professional persons). Two tutorials have been designed, introducing the SQL language and the QBD* environment, respectively