Such work typically trains semi-supervised classifiers to determine events of interest due to the limitation of annotated data.
a few studies devote to open domain event extraction (Benson et al., 2011;Ritter et al., 2012;Petrović et al., 2010;Diao et al., 2012;Chierichetti et al., 2014;Li et al., 2014;Qiu and Zhang, 2014), in which an event category is not predefined, and clustering models are applied to automatically induce event types.