Abstract: A data base query submitted in natural speech normally requires a dialog with the data base system, which repeatedly prompts the user to submit further statements. From each speech utterance submitted by the user a plurality of sets of statements are derived. The statements in these sets are tested for consistency with stored statements determined previously and consistent new statements are stored and stored statements are corrected or verified. Moreover, the stored statements are basically used in each dialogue step in order to derive from these statements an optimum request for the user by the system. Preferably, the statements are also stored with probability values or reliability values, the corresponding values of new statements to be stored being derived from the reliabilities of the statements of the respective speech utterance and the corresponding consistent statements stored.