32. A non-transitory computer readable storage medium storing one or more programs for execution by one or more processors of a computer system, the one or more programs comprising instructions for: receiving a factual query; identifying a set of possible factual answers to the factual query by searching a fact repository that stores factual information extracted from a plurality of documents; determining for each of the possible factual answers a respective score; identifying first answers of the set of possible factual answers to the factual query with best scores; for each of the first answers: identifying, as answers that support the respective first answer, second answers of the possible factual answers that support the respective first answer; and determining a supported score by mathematically combining the score of the respective first answer and the scores of the second answers; identifying a third answer of the first answers with a best supported score; and generating a response including the third answer only if the best supported score exceeds a predefined threshold.
32. A non-transitory computer readable storage medium storing one or more programs for execution by one or more processors of a computer system, the one or more programs comprising instructions for: receiving a factual query; identifying a set of possible factual answers to the factual query by searching a fact repository that stores factual information extracted from a plurality of documents; determining for each of the possible factual answers a respective score; identifying first answers of the set of possible factual answers to the factual query with best scores; for each of the first answers: identifying, as answers that support the respective first answer, second answers of the possible factual answers that support the respective first answer; and determining a supported score by mathematically combining the score of the respective first answer and the scores of the second answers; identifying a third answer of the first answers with a best supported score; and generating a response including the third answer only if the best supported score exceeds a predefined threshold. 35. The computer readable storage medium of claim 32 , wherein respective factual answers of the subset are associated with respective attributes and attribute-values in the fact repository; and the instructions for identifying, as answers that support the respective first answer, second answers of the set of possible factual answers include instructions for identifying, as answers that support the respective first answer, second answers of the set of possible factual answers that are distinct from the respective first answer and support the respective first answer in accordance with respective attributes and attribute-values associated with the first answer and respective answers of the second answers.