Resolving Anaphors in Embedded Sentences

Resolving Anaphors in Embedded Sentences Saliha Azzam University of Sheffield Department of Computer Science Regent Court 211 Portobello Street Sheffield S1 4DP U.K. S. Azzam~dcs. shef. ac. uk Abstract We propose an Mgorithm to resolve anaphors, tackling mainly the problem of intrasentential antecedents. We base our methodology on the fact that such an- tecedents are likely to occur in embedded sentences. Sidner's focusing mechanism is used as the basic algorithm in a more com- plete approach. The proposed algorithm has been tested and implemented as a part of a conceptual analyser, mainly to pro- cess pronouns. Details of an evaluation are given. 1 Introduction Intrasentential antecedents, i.e., antecedents occur- ring in the same sentence as the anaphor, are a cru- cial issue for the anaphora resolution method. The main problem is to determine the constraints that intrasentential phrases must respect in anaphoric re- lations. These constraints are used to determine re- lations between a given anaphor and its antecedents. Until now, this kind of constraint has been tackled mainly in terms of syntactic aspects, see (Lappin and Leass, 1994) (Merlo, 1993) and (Hobbs, 1985). We propose to consider new kinds of criteria that com- bine semantic restrictions with sentence structure. One of these criteria is, for example, the way in which the verb meaning influences the sentence structure, then the way in which the sentence struc- ture influences the anaphoric relations between in- trasentential phrases. The structure we studied is the embedded sentence structure. Indeed, an im- portant assumption we have made is that embedded sentences favour the occurrence of intrasentential an- tecedents. We exploit the focusing mechanism pro- posed by Sidner (Sidner, 1979) (Sidner, 1981) (Sial- her, 1983) extending and refining her algorithms. The algorithm is designed for anaphors generally, even if we focus mainly on pronouns in this paper. Indeed, the distinction between different kinds of anaphors is made at the level of anaphor interpreta- tion rules. These resolution rule aspects will not be developed here; though they have been developed in the literature, e.g., see (Carter, 1987), and (Sidner, 1981) (Sidner, 1983). We focus more on the mecha- nisms that handle these different kinds of rules. We first present how intrasentential antecedents occur in embedded sentences. We recall the main ideas of the focusing approach, then expand on the main hypotheses which led the design of the anaphora resolution algorithm. 2 Intrasentential Antecedents 2.1 Embedded sentences and elementary events An embedded sentence contains either more than one verb or a verb and derivations of other verbs (see sentence 1 with verbs said and forming). 1) Three of the world's leading advertis- ing groups, Agence Havas S.A. of France, Young & Rubicam of the U.S. and Dentsu Inc. of Japan, said they are forming a global advertising joint venture. Broadly speaking embedded sentences concern more than one fact. In sentence 1 there is the fact of saying something and that of forming a joint venture. We call such a fact an elementary event (EE hereafter). Thus an embedded …

Content truncated to 500 words