2It is worth noting that this formalization subsumes both directed and undirected linear-chain graphical models, which are the most typical models for sequence labeling, including HMM and CRF.
if the elements of V 1 are aligned into regular time slices, and the nodes in each time slice are associated with possible assignments of labels for that time, we obtain the representation equivalent to the ordinary linear-chain graphical models, in which all possible label assignments for each state are expanded.