Resolving Ellipsis in Clarification

Resolving Ellipsis in Clarification Jonathan Ginzburg Dept of Computer Science King’s College, London The Strand, London WC2R 2LS UK ginzburg@dcs.kcl.ac.uk Robin Cooper Dept of Linguistics G¨oteborg University Box 200, 405 30 G¨oteborg, Sweden cooper@ling.gu.se Abstract We offer a computational analysis of the resolution of ellipsis in certain cases of dialogue clarification. We show that this goes beyond standard techniques used in anaphora and ellipsis resolu- tion and requires operations on highly structured, linguistically heterogeneous representations. We characterize these operations and the representations on which they operate. We offer an analy- sis couched in a version of Head-Driven Phrase Structure Grammar combined with a theory of information states (IS) in dialogue. We sketch an algorithm for the process of utterance integration in ISs which leads to grounding or clarifi- cation. 1 Introduction Clarification ellipsis (CE), nonsentential ellipti- cal queries such as (1a(i),(ii)) are commonplace in human conversation. Two common read- ings/understandings of CE are exemplified in (1b,c): the clausal reading is commonly used sim- ply to confirm the content of a particular subutter- ance. The main function of the constituent read- ing is to elicit an alternative description or osten- sion to the content (referent or predicate etc) in- tended by the original speaker of the reprised sub- utterance. (1) a. A: Did Bo finagle a raise? B: (i) Bo?/ (ii) finagle? b. Clausal reading: Are you asking if BO (of all people) finagled a raise/Bo FI- c.NAGLED a raise (of all actions) Constituent reading: Bo?/What does it mean to finagle?Who is The issue of whether CE involves an ambi- guity or is simply vague is an important one.1 � 2 Clearly, pragmatic reasoning plays an important role in understanding CEs. Some considerations do, nonetheless, favour the existence of an ambi- guity. First, the BNC provides numerous exam- ples of misunderstandings concerning CE inter- pretation,3 where a speaker intends one reading, is misunderstood, and clarifies his original inter- pretation: (2) a. A: ... you always had er er say every foot he had with a piece of spunyarn in the wire/B: Spunyarn?/A: Spunyarn, yes/B: What’s spunyarn? b. A: Have a laugh and joke with Dick./ B: Dick?/A: Have a laugh and joke with Dick./B: Who’s Dick? 1An anonymous ACL reviewer proposed to us that all CE could be analyzed in terms of a single reading along the lines of “I thought I heard you say Bo, and I don’t know why you would do so?”. 2Closely related to this issue is the issue of what other readings/understandings CE exhibits. We defer discussion of the latter issue to (Purver et al., 2001), which provides a detailed analysis of the frequency of CEs and their under- standings among clarification utterances in the British Na- tional Corpus (BNC). 3This confirms our (non-instrumentally tested) impres- sion that these understandings are not on the whole disam- biguated intonationally. All our CE data from the BNC was found using SCoRE, Matt Purver’s dialogue oriented BNC search engine (Purver, 2001). More crucially, the clausal and constituent readings involve …

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