We use the CRF implementation in CRFsuite (Okazaki, 2007) and scikit-learn (Pedregosa et al., 2011) with the L-BFGS training algorithm (default) and Elastic Net (L1 + L2) regularization.
we train two classifiers: the first one takes as input a sentence and predicts the negation cue BIO labels, and the second one takes as input a sentence along with information about the predicted cues and predicts the scope BIO labels.