3 As mentioned in the introduction, since each word can trigger multiple event mentions having different types/subtypes, we train one CRF for each type.
for classifier of 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 (Bs 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).