Partial Orderings and Aktionsarten in Discourse Representation Theory

Partial Orderings and Aktionsarten in Discourse Representation Theory lOtrt EBERLE Institut for Maschinelle Spraehverarbeitung Universit~it Stuttgart Keplerstr.17 7000 Stuttgart West Germany Abstract This paper presents an approach to deal with the underspecification of Aktionsarten in German sentences. In German the difference between an accomplishment and the associated progressive state is often not marked on the sentence level. This distinction is important for correctly interpreting texts and for translation into languages which provide morphological markings of Aktionsarten. To maintain compositionality we suggest a two-step analysis of a text with respect to the temporal relations and the classification as events or states. This analysis is guided by the Discourse Representation Theory developed by Kamp and makes use of world knowledge and an inference component. The problem of classification can be reformulated as the problem of finding an embedding function f from the representational entities onto the domain of a model. The models we use are structures built from intervals of time, events and individuals. Considering intensional models of this type will allow us to give truth-conditions for progressive states related to corresponding accomplishments. We restrict ourselves to progressive states of intentional actions and use the beliefs of the agent. 1) Introduction: The influence of the criterion "Aktionsart" with respect to the temporal relations of temporal entities often seems to be overemphasized. On the one hand the correct dassiftcation is a problem, on the other hand, it seems that in more cases than assumed the influence of world knowledge is necessary to disambiguate the temporal relations. In this paper an approach is preseuted based on a two-step anal~Ls of a text. The first step consists in constructing a partial ordering on the basis of an approximate classification of the temporal units on sentence level, using the framework of D(iscourse) R(epresentatlon) T(heory)/cf.Kamp 1981a/. In the second step we try to obtain possible linear readings, using background-information, provided by a database, and an inference component that. is an extended version of the "event-calculus" /cf.Kowalski,Sergot/. The subdivision into two steps enables the temporal resolution component to work without a great number of inferencing processes. This contributes to a more modular-like structuring of the natural language processing-system. The goal is to represent ambiguous readings as such. The progressive state reading of an accomplishment leads to the problem called "imperfeetive paradox". Using the beliefs of the agent we try to give a solution for the subclass of intentional actions. The problem here is to deal with the time dependency of the content of someone's belief. 160 2) Partial Event-Structures The starting point of this paper is the conviction, following Kamp and others, that within the temporal units, events are primordial, and time is abstracted from them. The construction of pure temporal units can be based on the ultra-filter-construction introduced by Wiener /cf.Kamp 1979,1981b,van Benthem/: In order to model the natural underspecification of human perception, only the relations < , o (temporally smaller or overlap) are given within the event-structures in /Kamp 1979/along with the following axioms: A1 V …

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