5. The requirement acquisition method according to claim 4 , further comprising: calculating a distance between each of the plurality of character strings and the document; and extracting a character string among the plurality of character strings the distance thereof is minimum as the candidate character string.
5. The requirement acquisition method according to claim 4 , further comprising: calculating a distance between each of the plurality of character strings and the document; and extracting a character string among the plurality of character strings the distance thereof is minimum as the candidate character string. 6. The requirement acquisition method according to claim 5 , wherein the distance between each of the plurality of character strings and the document is calculated based on an approximation calculation method of a Kolmogorov complexity.