grammar set, which accounts for a wider array of permutations of a given response (e.g. "balance was wrong", "wrong balance", "balance is high", "high balance"). Despite the greater amount of data and processing required for open-ended prompts, they are more interactively efficient, as the prompts themselves are typically much shorter.

A mixed dialogue approach involves shifting from open-ended to directed dialogue or vice versa within the same interaction, as one type of prompt may be more effective in