9. A system for responding to a voice inquiry from a user during a session between the user and the system, the system comprising at least one processor configured to: recognize speech in the voice inquiry from the user, and respond to the inquiry; store a dialog history with the user in a dialog history log; responsive to a determination that the system cannot provide a valid system response to spoken input items, estimate a current dialog state of the user, based on the dialog history log and a dialog state determination model comprising information for estimating the current dialog state according to the dialog history log from the service start time to the current time; and display remotely from the user a dialog state diagram, including a representation of each expected dialog state for the session, and further including a representation of at least one dialog state, other than a transition between dialog states, not yet entered during the session, according to a dialog state diagram definition file defining each expected dialog state for the session and at least information regarding display of the dialog state diagram, and visually present the estimated current dialog state on the dialog state diagram to an operator other than the user.
14. The system according to claim 9 , wherein the at least one processor is further configured to highlight the estimated current dialog state on the dialog state diagram.