On Representing the Temporal Structure of a Natural Language Text

On Representing the Temporal Structure of a Natural Language Text* Kurt Eberle Institut fiir Maschinelle Sprachverarbeitung Universit£t Stuttgart Azenbergstrafle 12 7000 Stuttgart Germany Net address: kurt@adler.philosophie.uni-stuttgart.de Abstract A proposal to deal with tenses in the framework of Discourse Representation Theory is presented, ms it has been implemented for a fragment at the IMS for the project LILOG. It is based on the theory of tenses of H. Kamp and Ch. Rohrer. The system uses tile tense and aspect information, the information about the temporal discourse structure of tile preceding text stored in a specific list of possible reference times, and background knowledge. These types of information interact in order to choose a suited temporal anchor for the event of a new sentence. With respect to extended texts, choosing the right reference time for a new event is a problem which has been largely neglected in the literature. 1 Introduction In Reichenbach (1947) the tenses are analyzed into different orderlngs of the relevant temporal parame- ters which are: the time of the event talked about, the speech time (time of utterance) and the reference time. Simple past, for instance, identifies event- and reference-time, which are both before the speech time. In the case of past perfect the event time precedes the reference time which precedes the speech time. Kanlp attd Rohrer (1983,1985) were led by text- phenomena to split up the Reichenbachian reference time into two contextually given coordinates: the ref- erence time (in the narrow sense) and the temporal perspective time. (1) Harry handed the book about giraffes to Jane (el). Two hours ago he had descovered it in Alfred's book- shop (e2). He had bought it (es), had inserted a dedi- cation (e4) and had it wrapped up (e~). Jane took the book with a smile (e~) In (1), the events e2 - e5 are ordered consecutively, *This research has been done in the context of LILOG. Thanks on this way to the members of the LILOG-researeh group of IBM for helpfull comments and especially for having made the integration of the suggested system in the LILOG- prototype possible. each taking its predecessor as reference time, with the exception that the context does not provide au event which precedes e2 and which, therefore, could play the role of reference time with respect to e2. Tile whole sequence e2 - es is seen from a vantage point in the past, el, which, therefore, plays the role of perspective time with regard to the structural inte- gration of e2 - c5. The perspective from which e 1 and es are seen is the speech tinle, e t serves as reference time for c~. In the approach of Kamp and Rohrer the role that the reference time plays in Reichenbach's system is taken over by the perspective time with re- spect to the meaning of the tenses in single sentence discourses: The meaning (one of tile meanings) of past perfect is that the event tittle precedes the perspec- tive time which precedes …

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