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…
X. Yan, J. Guo, Y. Lan, and X. Cheng. Proceedings of the 22nd International Conference on World Wide Web, page 1445–1456. New York, NY, USA, Association for Computing Machinery, (2013)
S. Shaw, D. Dicks, V. Venkatesh, G. Lowerison, and D. Zhang. Information Technology Based Proceedings of the FIfth International Conference onHigher Education and Training, 2004. ITHET 2004., page 598-603. (2004)
A. Chiu, and A. Fu. Database Engineering and Applications Symposium, 2003. Proceedings. Seventh International, page 298--307. IEEE, (2003)Best paper award.
W. Jin, A. Tung, and J. Han. Proceedings of the seventh ACM SIGKDD international conference on Knowledge discovery and data mining, page 293--298. ACM, (2001)
J. Weng, E. Lim, J. Jiang, and Q. He. Proceedings of the Third ACM International Conference on Web Search and Data Mining, page 261–270. New York, NY, USA, Association for Computing Machinery, (2010)