Lafferty, J. D., McCallum, A. & Pereira, F. C. N. (2001). Conditional Random Fields: Probabilistic Models for Segmenting and Labeling Sequence Data. Proceedings of the Eighteenth International Conference on Machine Learning (p./pp. 282--289), San Francisco, CA, USA: Morgan Kaufmann Publishers Inc.. ISBN: 1-55860-778-1