Reasoning about the temporal structure of narratives

Narratives are a type of discourse used to describe sequences of events. Standard examples of narratives are novels, short-stories, biographies, and histories. Narratives can be contrasted with other discourse types, such as lyric poetry and expository prose, in which the temporal element is not so central. Because of the nature of narratives, one of the most important tasks for understanding them is determining the temporal relations that exist among the events described in the narrative. These events and their temporal relations constitute what is called the story of the narrative. This dissertation concentrates on the study of issues involved in understanding the temporal structure of narratives. These issues are of two major types: (1) how can the events of a story and the temporal relationships that hold among these events be represented, and (2) how does the reader determine the temporal relationships that hold among the story events. Central to our discussion are the concepts of the narrative now-point and the narrative-line. The narrative now-point is a special Reference-Time which is used to represent the present moment within the story. At least part of the analysis of how different tenses, aspects, and time adverbials function within a narrative involves their interaction with, and effects on, this now-point. We define a narrative-line as a stretch of narrative which is controlled by, or is within the scope of, a single now-point. We further define a basic narrative-line as a narrative-line which contains no time adverbials and which follows certain other simplifying restrictions. By restricting ourselves to such "well-behaved" narratives, we can define a simple set of general rules for extracting the temporal structure of a story from such a narrative. The only factors taken into consideration by these rules are tense, aspect, event-type, and the Narrative Convention, which says that unless we (the readers) are given some signal to the contrary, we assume that the events of the story occurred in the order in which they are presented in the text. This type of narrative, and the set of discourse rules defined on it, constitute a base case upon which more complex types of narratives can be defined. We then extend the rules from this base case to cover narrative-lines which contain various types of time adverbials, including frame adverbials, adverbials of duration, and relational adverbials. Next, we extend our analysis to more large-scale narratives, which we show can be understood as consisting of one or more narrative-lines, each of which requires its own now-point. Finally, we describe our implementation of a parser which can read a narrative-line which includes frame adverbials and adverbials of duration. As output, the parser builds a model of the events of the story, with the temporal relations which hold among those events.