A binary indicator x, which is generated by a Bernoulli distribution π x drawn from a Beta distribution with symmetric hyperparameter γ x , determines whether a word is generated by ψ z or ψ e .
moreover, there was work (Verhagen et al., 2005;Chambers and Jurafsky, 2008;Bethard, 2013;Chambers, 2013;Chambers et al., 2014) about temporal event extraction and tracking.