1. One or more computer-storage media having computer-executable instructions embodied thereon that, when executed by one or more computing devices, perform a method of generating a natural language output, the method comprising: receiving a query from a user; identifying an answer to the query; mapping the answer to structured data from a knowledge base; identifying a sentence structure associated with the structured data; identifying one or more constraints associated with the sentence structure are satisfied such that only valid sentence structures are output; and upon satisfying each of the one or more constraints, communicating an output answer to the query in the form of a sentence.