Right Association Revisited

RIGHT ASSOCIATION REVISITED * Michael Niv Department of Computer and Information Science University of Pennsylvania Philadelphia, PA, USA niv@linc, cis.upenn.edu Abstract Consideration of when Right Association works and when it fails lead to a restatement of this parsing prin- ciple in terms of the notion of heaviness. A computa- tional investigation of a syntactically annotated corpus provides evidence for this proposal and suggest circum- stances when RA is likely to make correct attachment predictions. 1 Introduction Kimball (1973) proposes the parsing strategy of Right Association (RA). RA resolves modifiers attachment am- biguities by attaching at the lowest syntactically per- missible position along the right frontier. Many au- thors (among them Wilks 1985, Schubert 1986, Whit- temore et al. 1990, and Weischedel et al. 1991) in- corporate RA into their parsing systems, yet none rely on it solely, integrating it instead with disambiguation preferences derived from word/constituent/concept co- occurrence based. On its own, RA performs rather well, given its simplicity, but it is far from adequate: Whitte- more et al. evaluate RA's performance on PP attachment using a corpus derived from computer-mediated dialog. They find that RA makes correct predictions 55% of the time. Weischedel et al., using a corpus of news sto- ries, report a 75% success rate on the general case of attachment using a strategy Closest Attachment which is essentially RA. In the work cited above, RA plays a relatively minor role, as compared with co-occurrence based preferences. The status of RA is very puzzling, consider:. (1) a. John said that Bill left yesterday. b. John said that Bill will leave yesterday. "I wish to thank Bob Frank, Beth Ann Hockey, Yonng-Snk Lee, Mitch Marcus, Ellen Prince, Phil Resnik, Robert Rubinoff, Mark Steedman, and the anonymous referees for their helpful suggestions. This research has been supported by the following grants: DARPA N00014-90-J-1863, ARt DAAL03-89-C-0031, NSF IRI 90-16592, Ben Franklin 91S.30"/8C-1. 285 (2) In China, however, there isn't likely to be any silver lining because the economy remains guided primarily by the state. (from the Penn Treebank corpus of Wall Street Journal articles) On the one hand, many naive informants do not see the ambiguity of la and are often confused by the putatively semantically unambiguous lb - a strong RA effect. On the other hand (2) violates RA with impunity. What is it that makes RA operate so strongly in 1 but disappear in 2? In this paper I argue that it is an aspect of the declarative linguistic competence that is operating here, not a principle of parsing. 2 Heaviness Quirk et al. (1985) define end weight as the ten- dency to place material with more information content after material with less information content. This notion is closely related with end focus which is stated in terms of importance of the contribution of the constituent, (not merely the quantity of lexical material.) These two prin- ciples operate in an additive fashion. Quirk et al. use heaviness to account for a variety of phenomena, among them: • genitive …

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