5. The information extraction system according to claim 1 , wherein the identification information specification unit implemented at least by the hardware compares a positive example element vector and a negative example element vector, and specifies a constituent element having a large value in the positive example element vector as the positive example identification information and specifies a constituent element having a large value in the negative example element vector as the negative example identification information, the positive example element vector storing, for each constituent element of sentences included in the positive example solution request sentence set, the number of occurrences of the constituent element in the positive example solution request sentence set, and the negative example element vector storing, for each constituent element of sentences included in the negative example solution request sentence set, the number of occurrences of the constituent element in the negative example solution request sentence set.
6. The information extraction system according to claim 5 , wherein the identification information specification unit implemented at least by the hardware excludes a constituent element relating to a word having a low co-occurrence frequency with the problem evoking expression in the positive example element vector, and excludes a constituent element relating to a word having a low co-occurrence frequency with the problem evoking expression in the negative example element vector.