tokens: Some other IE paradigms such as Open IE Etzioni05unsupervisednamed - entity , banko2007open , banko2008tradeoffs , etzioni2011open , ritter2012open , Pre - emptive IE shinyama2006preemptive , On - demand IE sekine2006demand , Liberal IE huangliberal , huang2017liberal , and semantic frame based event discovery Kim2013 can discover many events without pre - defined event schema .