7. The method of claim 6 , where the candidate phrases exclude the seed phrases.
6. The method of claim 1 , where the received phrase candidates are generated by: receiving a set of seed phrases, each with an estimate of a fraction of documents belonging to a particular topic among all documents containing the seed phrase; receiving an estimate of a fraction of all documents belonging to the topic; using the received seed phrases and estimates as an input along with a collection of labeled documents and a collection of unlabeled documents to train a linear classifier that approximately reproduces the estimated fractions; and using phrases identified by training the linear classifier as candidate phrases.