[1] D. Jurafsky, J. Martin: Speech and Language Processing.
see https://web.stanford.edu/~jurafsky/slp3/
[2] The Natural language Toolkit.
see http://www.nltk.org/
[3] J. Allen: Natural Language Understanding (Pearson)
[4] C. Manning, H. Schütze: Foundations of Statistical Natural Language Processing (MIT Press)
[5] S. Russel, P. Norvig: Artificial Intelligence, A Modern Approach (Pearson)
[6] S. Bird, E. Klein, E. Loper: Natural Language Processing with Python (OReilly).