Case Role Filling as a Side Effect of Visual Search

CASE ROLE FILLING AS A SIDE EFFECT OF VISUAL SEARCH Heinz Marburger Research Unit for Information Science and Artificial Intelligence University of Hamburg Mittelweg 179 D-2000 Hamburg 13, F.R. Germany Wolfgang Wahlster FBI0 - Angewandte Mathematlk und informatlk University of SaarbrOcken Im Stadtwald 0-6600 Saarbr0cken 11, F.R. Germany ABSTRACT This paper addresses the problem Of generating communicatively adequate extended responses in the absence of specific knowledge concerning the intensions of the questioner. We formulate and justify a heuristic for the selection of optional deep case slots not contained in the question as candidates for the additional information con- tained in an extended response. It is shown that, in a visually present domain of discourse, case role filling for the construction of an extended response can be regarded as a side effect of the visual search necessary to answer a question con- taining a locomotion verb. The paper describes the various representation constructions used in the German language dialog system HAM-ANS for dealing with the semantics of locomotion verbs and illus- trates their use in generating extended responses. In particular, we outline the structure of the geometrical scene description, the representation of events in a logic-oriented semantic representa- tion language, the case-frame lexicon and the representation of the referential semantics based on the Flavor system. The emphasis is on a detailed presentation of the application of object-oriented programming methods for coping with the semantics of locomotion verbs. The pro- cess of generating an extended response is illus-. trated by an extensively annotated trace. 1. INTRODUCTION Frequently a questioner expects more than a direct, literal response although he must assume that the answerer is not informed about what par- ticular information he is seeking. The questioner imputes to a cooperative dialogue partner the com- municative competence to reply to a simple yes-no question like (I) with an extended response (cf. (12], (11]) like (la) rather than with a simple Yes. (I) Are you going to t r a v e l this summer? (la) Yes, to Sicily. In the absence of special information about the previous course of the dialog or the intentions of the questioner (the unmarked case) an answer l i k e (la) seems more appropriate than (Ib) or ( I c ) . (Ib) Yes, with an old school friend. (Ic) Yes, by plane. OF course, there are numerous dialog situatlons in which (lb) os" (lc) could be generated as a commun- icatively adequate response on the basis of a par. t±cular partner model. But it still must b~ asked why in dialogs of the type 'information ,upply' the unmarked response takes the form (la) ~nd not (lh) or (lc). In this paper we w i l l present the results of a computational study of this problem for the domain Research on HAM..ANS Is currently being supported by the German Ministry of Research and Technology (8MFT) under contract 081T15038 'locomotion verbs' in dialogs based on a visually present world of discourse. This question is par- ticularly important …

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