Recall that since each (multi-)word may trigger multiple event mentions having different (sub)types, we train one CRF for each type.
to train the CRF for type t j , we create one instance for each word w i , assigning it a class label that indicates whether it begins a trigger with subtype s jk (B-s jk ), is inside a trigger with subtype s jk (I-s jk ), begins a trigger with other types (B-t m =j ), is inside a trigger with other types (I-t m =j ) or is outside a trigger (O).