Extracting topics is a good unsupervised data-mining technique to discover the underlying relationships between texts. There are many different approaches with the most popular probably being LDA but…
A. Chiu, и A. Fu. Database Engineering and Applications Symposium, 2003. Proceedings. Seventh International, стр. 298--307. IEEE, (2003)Best paper award.
W. Jin, A. Tung, и J. Han. Proceedings of the seventh ACM SIGKDD international conference on Knowledge discovery and data mining, стр. 293--298. ACM, (2001)