Representing Implicit and Explicit Time Relations in Narrative

Abstract

This paper describes a representation for time relations in narrative. The time relations are based on both explicit sources of time information (e.g., adverbial expressions or tense) and implicit sources, such as multiple reference to a single event, narrative time progression and earlier events implied by change of state words. Natural language processing is used to analyse the input text into a set of subject-verb-object units, connected by binary connectives; these units correspond to the events of the narrative. With each event is associated a time in relation to another event, adjusted by an optional time quantity. These time relations have a natural representation as a directed graph whose nodes are time points and whose edges are time intervals. The algorithm for extracting the time relations from a text is illustrated for an excerpt from a hospital discharge summary.