The MSM2013 corpus has 4 types of named entities, person (PER), location (LOC), organization (ORG), and miscellaneous (MISC).
qu and Liu (2012) used the pairwise CRF with a 4-connected neighborhood system (2D CRF) as their graphical model, where each vertex in the graph represents a sentence pair, and each edge connects adjacent source sentences or target sentences.