In the literature, most of existing studies on event extraction concern English and can be classified into either pattern-based (e.g., Riloff, 1996;Yangarber et al., 2000;Stevenson and Greenwood, 2005;Shinyama and Sekine, 2006;Patwardhan and Riloff, 2007;Chambers and Jurafsky, 2011) or classifier-based (e.g., Grishman et al., 2005;Ahn, 2006;Hardy et al., 2006;Maslennikov and Chua, 2007;Ji and Grishman, 2008;Patwardhan and Riloff, 2009;Liao and Grishman, 2010;Hong et al., 2011;Lu and Roth, 2012;Llorens et al., 2012).
while earlier studies focus on sentence-level extract ion, later ones turn to employ global info rmation.