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. Author manuscript; available in PMC: 2017 Jan 13.
Published in final edited form as: JMLR Workshop Conf Proc. 2016 Jun 11;48:334–343.

Figure 1.

Figure 1

Figure (a) shows a factor graph model for a standard linear chain CRF over a length-four sequence. (b) shows a two-level hierarchical CRF where the first level labels are grouped into fixed size blocks at the second level, which has linear chain structure. Figure (c) shows a two-level version of the proposed model, which includes a quadratic number of second level span variables, one for each possible span. The global coordinating factor that ensures a valid segmentation connects to all second-level span variables and is not pictured. Figures (d)-(f) show example segmentations and labelings for a length four sequence. Our model (c) represents a distribution over both active spans and labels conditioned on the input features.