A Discourse Copying Algorithm for Ellipsis and Anaphora Resolution

A Discourse Copying Algorithm for Ellipsis and Anaphora Resolution Andrew Kehler Harvard University Aiken Computation Laboratory 33 Oxford Street Cambridge, MA 02138 kehler@das.harvard.edu Abstract We give an analysis of ellipsis resolution in terms of a straightforward discourse copying algorithm that correctly predicts a wide range of phenomena. The treat- ment does not suffer from problems inher- ent in identity-of-relations analyses. Fur- thermore, in contrast to the approach of Dalrymple et al. [1991], the treatment di- rectly encodes the intuitive distinction be- tween full NPs and the referential elements that corefer with them through what we term role linking. The correct predictions for several problematic examples of ellip- sis naturally result. Finally, the analysis extends directly to other discourse copying phenomena. 1 Introduction A simple example of verb phrase (VP) ellipsis is given in sentence (1): (1) John likes his mother, and Bill does too. The stranded auxiliary in the second clause indi- cates the deletion of a verb phrase, the meaning of which is to be determined from another clause, in this case, the first clause. Following Dalrymple, et al. [1991], we term the clause that the VP is copied from the source clause, and the clause which contains the elided VP the target clause. As is well established in the literature, referential elements 1 in the source clause VP may give rise to strict/sloppy ambiguities 1 For present purposes, we will use the term referential elements as synonymous with pronouns. In Section 5 we discuss how this class may be extended to include implicit arguments as well. in the target clause; for example in sentence (1) the target clause may receive one of two readings, namely one in which Bill likes John's mother (the strict read- ing), and one in which Bill likes his own mother (the sloppy reading). In this paper we address the distribution of strict and sloppy readings in VP-ellipsis and other anaphoric phenomena. In Section 2 we discuss prob- lems with past approaches, as well as support our decision to treat ellipsis resolution as a primarily se- mantic process. In Section 3 we give a representation for events that exhibits what we term role linking between referential elements and their referents, and describe an algorithm for ellipsis resolution that uses this representation. Section 4 demonstrates how use of this representation and algorithm results in the correct analysis of several problematic cases of ellip- sis without appeal to additional constraints. In Sec- tion 5 we argue that the strict/sloppy distinction is not a property of ellipsis alone, but is instead inher- ent in what we term the discourse copying process. Several discourse copying phenomena at the event and NP level are shown to be accounted for by our algorithm. We conclude in Section 6. 2 Past Approaches Much attention has been paid to the ellipsis prob- lem in linguistics (e.g., [Dahl, 1972; Dahl, 1974; Fiengo and May, 1990; Gawron and Peters, 1990; Ha'lk, 1987; Hellan, 1988; Klein, 1987; Lappin, 1992; Sag, 1976; Williams, 1977]), as well …

Content truncated to 500 words