1. A voice interactive system for responding to a voice inquiry from a user during a session between the user and the system, comprising: a combination of hardware and software configured to embody: a voice interactive unit for recognizing speech in the voice inquiry from the user and providing responses to the inquiry; a dialog history log for storing a record of a dialog between the voice interactive unit and the user; a dialog state diagram definition file for defining each expected dialog state for the session and information regarding at least display of a dialog state diagram; a dialog state determination model comprising information for estimating a current dialog state according to the dialog history log from a service start time to a current time; a dialog information analyzing unit, responsive to a determination by the voice interactive unit that it cannot provide a valid response to the voice inquiry from the user, for estimating the current dialog state between the user and the voice interactive unit based on the dialog history log and the dialog state determination model; and a dialog state display unit remote from the user for displaying the 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 the dialog state diagram definition file, and for visually presenting the current dialog state estimated by the dialog information analyzing unit on said dialog state diagram to an operator other than the user.