2. A method of generating a mixed-initiative dialog to obtain information for a set of information slots in a voice dialog system capable of receiving voice inputs from a user via at least one audio input interface and providing voice prompts to the user via at least audio output interface, the method comprising computer implemented steps performed by the voice dialog system, the method comprising: using at least one computer to perform steps comprising: selecting a subset of slots from the set of information slots, dependent upon a set of unfilled slots for which information is to be obtained in a current dialog cycle; constructing a composite grammar dependent upon the selected subset of slots, comprising: selecting from specified grammar composition rules those rules that apply to the selected subset of slots; forming a slot grammar for each slot in the selected subset of slots using at least one corresponding rule in the selected grammar composition rules; and combining the slot grammars using the selected grammar composition rules to produce the composite grammar, said composite grammar being applicable to permutations of the selected subset of slots; generating a prompt dependent upon the selected subset of slots; receiving a user response to the prompt via the at least one audio interface; comparing the response to the composite grammar; and determining, dependent upon the comparing step, if the response provides relevant information for the set of unfilled slots.
6. The method of claim 2 , all the limitations of which are incorporated herein by reference, wherein the selecting step is dependent upon at least one of a previous user response, a history of dialog-interaction which includes previous prompts and responses, a desired dialog flow, as yet unfilled slots in the set of information slots, and the selected subset of slots.