It is important to note that our interval-based formulation is more concise in terms of the number of variables and constraints needed in the ILP relative to time expression-based (or timepoint-based) formulations used in previous work (Chambers and Jurafsky, 2008).
in such timepoint-based formulations, the relation between each event mention and each time expression needs to be inferred, resulting in |E||T ||R T | variables, where |E|, |T |, and |R T | are the numbers of event mentions, time points, and temporal relations respectively.