A method and apparatus for controlling an interactive human-machine interface, which includes an input device and comprises a set of states. The set of states form a network through which data can be passed as a token. In a dialogue control unit, future states are assessed to determine allowable user inputs that may be received from the user. Each portion of the user input is stored in an associated node of the token, for use in the current state or in another of the active states. Each node is checked to see if it relates to the current state, and if so, then the portion of the user input stored in the node is processed.