What is algorithm of yahoo answers in retrieving candidates answers from answered question?

We know that every time a user posted a question, yahoo answers will return some candidates of answers from the answered question that it thinks that they are the answer for this question you have posted. May I know what is the information retrieval architecture/algorithm used behind it? could it be question to... show more We know that every time a user posted a question, yahoo answers will return some candidates of answers from the answered question that it thinks that they are the answer for this question you have posted. May I know what is the information retrieval architecture/algorithm used behind it? could it be question to question mapping, question to answer mapping, term overlapping or more than that (e.g. tf.idf or much more)?
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