5. The computer-implemented method of claim 3 , wherein determining a quality metric value for search results provided in response to the search query comprises determining a quality score that is a measure of user satisfaction in response to the search results, the measure of user satisfaction being dependent on user interactions with the search results at the user device from which the input sentence was received.
3. The computer-implemented method of claim 2 , wherein determining whether the first input sentence has an underserving signal further comprises, for each first input sentence: determining that the first input sentence was processed as a search query; determining a quality metric value for search results provided in response to the search query; and determining the first input sentence has the underserving signal when the quality metric value does not meet a threshold quality value.