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…
J. Weng, E. Lim, J. Jiang, и Q. He. Proceedings of the Third ACM International Conference on Web Search and Data Mining, стр. 261–270. New York, NY, USA, Association for Computing Machinery, (2010)