Temporal Reasoning In Natural Language Understanding: The Temporal Structure Of The Narrative

This paper proposes a new framework for discourse analysis, in the spirit of Grosz and Sid-ner (1986), Webber (1987a,b) but differentiated with respect to the type or genre of discourse. It is argued that different genres call for different representations and processing strategies; particularly important is the distinction between subjective, pefformative discourse and objective discourse, of which narrative is a primary example. This paper concentrates on narratives and introduces the notions of temporal focus (proposed also in Webber (1987b)) and narrative move. The processing tasks involved in reconstructing the temporal structure of a narrative (Webber's e/e structure) are formulated in terms of these two notions. The remainder of the paper analyzes the durational and aspectual knowledge needed for those tasks. Distinctions are established between grammatical aspect, as-pectual class and the aspectual perspective of a sentence in discourse; it is shown that in En-glish, grammatical aspect under-determines the aspectual perspective. NARRATIVES This paper investigates the varieties of temporal knowledge and temporal reasoning that are at work in understanding extended narratives. It starts out by developing a new framework for narrative representation, a framework that has developed independently from, but is very similar to Webber, 1987a, 1987b. It also builds on the ideas of Grosz and Sidner (1986), but refor-mulates them specifically for the task of narrative understanding. A reformulation, I believe, is needed because different genres of discourse-narrative, expository text, task-oriented dialog, argument, etc.-have different principles of organization that call for different representations and processing strategies. Without offering a comprehensive taxonomy of discourse genres I would llke to stress that narrative stands out by virtue of its two properties: it is objective and it unfolds in time. A distinction between subjective and objective modes of discourse has been drawn by many authors in linguistics and structuralist poetics, who all "have a category of narration to which another category is opposed; and they all agree that the non-narrative category is more subjective ~ (Lyone,1982:117). One manifestation of the objectivity of narratives is the structure of the underlying intentions. This structure plays an important role in Grosz and Sidner, 1986 who propose, inter alia, are that (a) the content of discourse is embedded in, and classified by, the speaker's intentions which form a hierarchical intentional structure, and (b) the content structure is separate from the attentional state, and both are rather indirectly represented by the linguistic material of discourse, organized in a hierarchical …