As the field of IE has developed, the focus of study has moved towards automatic knowledge acquisition for information extraction, including domain-specific lexicons (Riloff, 1993;Riloff and Jones, 1999) and extraction patterns (Riloff, 1996;Yangarber et al., 2000;Sudo et al., 2001).
methods have recently emerged for the acquisition of event extraction patterns without corpus annotation in view of the cost of manual labor for annotation.