1. http://onlinelibrary.wiley.com/doi/10.1111/j.1467--9868.2005.00503.x/full. http://onlinelibrary.wiley.com/doi/10.1111/j.1467--9868.2005.00503.x/full.
2. https://nlp.stanford.edu/software/CRF-NER.shtml. https://nlp.stanford.edu/software/CRF-NER.shtml.
3. http://www.cnts.ua.ac.be/conll2003/ner/. http://www.cnts.ua.ac.be/conll2003/ner/.
4. http://www.expertsystem.com/it/. http://www.expertsystem.com/it/.