Topic-based Multi-Document Summarization with Probabilistic Latent Semantic Analysis Leonhard Hennig author 2009-09 text Proceedings of the International Conference RANLP-2009 Galia Angelova editor Ruslan Mitkov editor Association for Computational Linguistics Borovets, Bulgaria conference publication hennig-2009-topic https://aclanthology.org/R09-1028/ 2009-09 144 149