7. The method of claim 1 , wherein all identical first keys are processed by a same reduce process that generates the first output.
1. A method, comprising: receiving textual input; processing, by one or more computers, the textual input to produce a first output comprising first keys, wherein each first key is an ngram occurring in the textual input; processing, by the one or more computers, the first output to produce a second output comprising second keys and associated second values, wherein each second key is an anchor extracted from at least one of the first keys, wherein each anchor is defined by a beginning portion and an ending portion of a respective first key ngram, the beginning portion and ending portion being separated by a middle portion of the respective first key ngram, and wherein each second value is a set of middle portions associated with each distinct anchor; and processing, by the one or more computers, the second output to produce a third output comprising third keys and associated third values, wherein each third key is a potential paraphrase pair identified from a second value set of middle portions, and each third value is a set of anchors associated with the potential paraphrase pair.