CLiFF Notes Research in the Language, Information and Computation Laboratory of the University of Pennsylvania Annual Report: 1994, No. 4 Technical Report MS-CIS-95-07 LINC Lab 282 Department of Computer and Information Science University of Pennsylvania Philadelphia, PA 19104-6389 Editors: Matthew Stone & Libby Levison cmp-lg/9506008 9 Jun 1995 i Contents I Introduction v II Abstracts 1 Breck Baldwin 2 Tilman Becker 4 Betty J. Birner 6 Sandra Carberry 8 Christine Doran 10 Dania Egedi 13 Jason Eisner 15 Christopher Geib 17 Abigail S. Gertner 19 James Henderson 21 Beth Ann Hockey 23 Beryl Hoffman 26 Paul S. Jacobs 28 Aravind K. Joshi 29 Jonathan M. Kaye 32 Albert Kim 34 Nobo Komagata 36 Seth Kulick 37 Sadao Kurohashi 38 Libby Levison 39 D. R. Mani 41 Mitch Marcus 43 I. Dan Melamed 46 ii Michael B. Moore 47 Charles L. Ortiz, Jr. 48 Martha Palmer 49 Hyun S Park 52 Jong Cheol Park 54 Scott Prevost 55 Ellen F. Prince 58 Lance A. Ramshaw 60 Lisa F. Rau 62 Jeffrey C. Reynar 64 Francesc Ribas i Framis 66 James Rogers 68 Bernhard Rohrbacher 70 Joseph Rosenzweig 72 Deborah Rossen-Knill 73 Anoop Sarkar 76 B. Srinivas 77 Mark Steedman 80 Matthew Stone 82 Anne Vainikka 84 Bonnie Lynn Webber 86 Michael White 89 David Yarowsky 91 III Projects and Working Groups 93 The AnimNL Project 94 The Gesture Jack project 96 Information Theory Reading Group 99 iii The STAG Machine Translation Project 100 The TraumAID Project 102 The XTAG Project 104 IV Appendix 107 iv Part I Introduction This report takes its name fromtheComputationalLinguistics Feedback Forum (CLiFF), an informal discussion group for students and faculty. However the scope of the research covered in this report is broader than the title might suggest; this is the yearly report of the LINC Lab, the Language, Information and Computation Laboratory of the University of Pennsylvania. It may at ®rst be hard to see the threads that bind together the work presented here, work by faculty, graduate students and postdocs in the Computer Science and Linguistics Departments,and the Institutefor Research in CognitiveScience. It includes prototypical Natural Language ®elds such as: Combinatorial Categorial Grammars, Tree Adjoining Grammars, syntactic parsing and the syntax- semantics interface; but it extends to statistical methods, plan inference, instruction understanding, intonation, causal reasoning, free word order languages, geometric reasoning, medical informatics, connectionism, and language acquisition. Naturally, this introductioncannot spell out all the connections between these abstracts; we invite you to explore themon your own. In fact, with thisissueit'seasier than ever to do so: this document is accessible on the ªinformation superhighwayº. Just call up http://www.cis.upenn.edu/˜cliff-group/94/cliffnotes.html In addition,you can ®nd many of the papers referenced in the CLiFF Notes on the net. Most can be obtained by following links from the authors' abstracts in the web version of this report. The abstracts describe the researchers' many areas of investigation, explain their shared concerns, and present some interesting work in CognitiveScience. We hope its new online format makes the CLiFF Notes a more useful and interesting guide to Computational Linguistics activity at Penn. v 1.1 Addresses Contributorsto this report can be contacted by writing to: contributor'sname department University of Pennsylvania Philadelphia, PA 19104 In addition, a list of publications from the Computer Science department may be obtained by contacting: Technical Report Librarian Department of Computer and Information Science University of Pennsylvania 200 S. 33rd St. Philadelphia, PA 19104-6389 (215)-898-3538 [email protected] 1.2 Funding Agencies This research is partially supported by: ARO including participation by the U.S. Army Research Laboratory (Aberdeen), Natick Laboratory, the Army Research Institute, the Institutefor Simulation and Training, and NASA Ames Research Center; Air Force Of®ce of Scienti®c Research; ARPA through General Electric Government Electronic Systems Division; AT&T Bell Labs; AT&T Fel- lowships; Bellcore; DMSO throughthe Universityof Iowa; General Electric Research Lab; IBM T.J. Watson Research Center; IBM Fellowships; National Defense Science and Engineering Graduate Fellowship in Computer Science; NSF, CISE, and Instrumentation and Laboratory Improvement Program Grant, SBE (Social, Behavioral, and Economic Sciences), EHR (Education & Human Re- sources Directorate); Nynex; Of®ce of Naval Research; Texas Instruments; U.S. Air Force DEPTH contract through Hughes Missile Systems. Acknowledgements Thanks to all the contributors. Comments about this report can be sent to: Matthew Stone or Libby Levison Department of Computer and Information Science University of Pennsylvania 200 S. 33rd St. Philadelphia, PA 19104-6389 [email protected] or [email protected] vi Part II Abstracts 1 Breck Baldwin Department of Computer and Information Science [email protected] Uniqueness, Salience and the Structure of Discourse Keywords: Discourse Processing, Anaphora Resolution, Centering, Pragmatics In spoken and written language, anaphora occurs when one phrase ªpoints toº another, where ªpoints toº means that the two phrases denote the same thing in one's mind. For example, consider the following quote from Kafka's The Metamorphosis: AsGregor Samsa awokeonemorningfromuneasy dreams hefound himself transformed in his bed into a gigantic insect. The proper noun Gregor Samsa isthe antecedent to theanaphor he, and the relationbetween them is termed anaphora. A thorny problem for those interested in modeling human language capabilities on computers is determining what an anaphor (the pointing phrase) picks out as its antecedent (the pointed-to phrase). Much of the dif®culty arises in picking the right antecedent when there are many to choose from. Since anaphora mediates the interrelatedness of language, accurately modeling this phenomenon paves the way to improvements in information retrieval, natural language interfaces and topic identi®cation. I have developed an approach that is particularly suitable for applications that require broad coverage and accuracy. My approach achieves broad coverage by applying simple and ef®cient algorithms to structurethepriordiscourse;it maintains accuracy by detecting the circumstances under which it is unlikely to make a good choice. A typical way to ®nd the antecedent of an anaphor is to impose a total order on the entities evoked by the prior discourse via some saliency metric, and then to take the descriptive content of the anaphor and search the saliency order for a matching antecedent Hobbs [1], Sidner [5], Luperfoy [4]. This approach has the ¯aw that for any two candidate antecedents, one is more salient than the other. But examples like; Earl and Ted were working together when ?he fell into the threshing machine. indicate that Earl and Ted are equally available as antecedents, hence the awkwardness of the example. My approach notes this problem by imposing a partial order on the entities of the prior discourse, which allows Earl and Ted to be equally salient, and requiring that there be a unique antecedent. These changes have greater import than addressing linguistic nit-picks. From an engineering perspective, the changes allow the algorithm to notice when it does not have enough information to ®nd a unique antecedent, and then appropriate fall back strategies can be used. For instance in quoted speech, it is better to wait for more information to arrive which follows the anaphor in the text so that the speaker is identi®ed, thereby resolving uses of I, you and me. This is particularly important when trying to ®nd inferred antecedents because it is a mechanism that can control search through knowledge bases±although I am just beginning to explore the possibilities in this area. The structuringportionof thetheory isachieved by assigninga part ofspeech tagsand identifying noun phrases with a simple regular expressions. Next, I assign a partial order to explicit and inferred entities using an amalgam of grammatical cues Hobbs [1], Lappin [3] which are triggered by regular 2 expression matches. A notion of local topic is provided by Centering Theory Grosz, Joshi and Weinstein [2]. Initial results show that the algorithm gets the correct antecedent for pronouns on the order of 85-90%, possessive pronouns 75% and the results for full de®nite NPs are still unknown± all percentages are for ambiguous contexts, i.e. two or more semantically acceptable candidate antecedents in the current and prior clause. References [1] Jerry Hobbs. Pronoun Resolution. Research Report No. 76-1, City College, City University of New York, 1976. [2] Barbara Grosz, Aravind Joshi and Scott Weinstein. Towards a Computational Theory of Discourse Interpretation. Manuscript, 1986. [3] Shalom Lappin and Herbert J. Leass. An Algorithmfor Pronominal Anaphora Resolution. To appear in Computational Linguistics. [4] Susan Luperfoy. The Representation of Multimodal User Interface Dialogues Using Discourse Pegs. Proceedings ofthe30thAnnualMeetingof theAssociationforComputationalLinguistics, 1992. [5] Candance L. Sidner. Focusing in the Comprehension of De®nite Anaphora. Readings in Natural Language Processing, eds Grosz, Jones, Webber. Morgan Kaufman, Los Altos CA. 1986. 3 Tilman Becker Postdoc, Institute for Research in Cognitive Science [email protected] Compact representation of syntactic knowledge Keywords: Syntax, Lexical rules In the framework of