8. A system comprising: a processor; and a non-transitory storage device storing instructions which, when executed by the processor, cause the processor to perform a method comprising: identifying a communicative goal in a speech input of a user; generating a plurality of sentence plans based on the communicative goal and a dialog history database, wherein each sentence plan of the plurality of sentence plans is a viable and potentially usable prompt in response to the speech input of the user; ranking the plurality of sentence plans to yield ranked sentence plans; and outputting at least one ranked sentence plan to yield an output sentence plan, wherein the output sentence plan provides a best sentence plan for generating a realization for the communicative goal from among the ranked sentence plans.
9. The system of claim 8 , the instructions further comprising: identifying a plurality of communicative goals; determining a priority communicative goal within the plurality of communicative goals; and ranking the plurality of sentence plans based at least in part on a comparison of the plurality of sentence plans and the priority communicative goal.