57. The computer-readable recording medium according to claim 52 , wherein the computer is further caused to execute the steps of: (f) estimating, for each unit of training, a density indicating a degree to which the unit of training contains the target information; and (g) generating feature data from the density estimated in the step (f) and the training data, and further acquiring a determination model usable in the determination performed in the step (b), using the feature data, wherein in the step (b), it is determined whether or not each sentence is target information in accordance with the determination model acquired in the step (g).
58. The computer-readable recording medium according to claim 57 , wherein in the step (f), for each unit of training, a density indicating a degree to which the unit of training contains the target information is estimated using the density estimation model acquired in the step (e).