Compilation of HPSG to TAG

Compilation of HPSG to TAG* Robert Kasper Dept. of Linguistics Ohio State University 222 Oxley Hall Columbus, OH 43210 U.S.A. kasper~ling.ohio-state.edu Bernd Kiefer Klaus Netter Deutsches Forschungszentrum ffir Kiinstliche Intelligenz, GmbH Stuhlsatzenhausweg 3 66123 Saarbrficken Germany (kieferlnetter}Qdfki.uni-sb.de K. Vijay-Shanker CIS Dept. University of Delaware Newark, DE 19716 U.S.A vijay@cis.udel.edu Abstract We present an implemented compilation algorithm that translates HPSG into lex- icalized feature-based TAG, relating con- cepts of the two theories. While HPSG has a more elaborated principle-based theory of possible phrase structures, TAG pro- vides the means to represent lexicalized structures more explicitly. Our objectives are met by giving clear definitions that de- termine the projection of structures from the lexicon, and identify "maximal" pro- jections, auxiliary trees and foot nodes. 1 Introduction Head Driven Phrase Structure Grammar (HPSG) and Tree Adjoining Grammar (TAG) are two frame- works which so far have been largely pursued in par- allel, taking little or no account of each other. In this paper we will describe an algorithm which will com- pile HPSG grammars, obeying certain constraints, into TAGs. However, we are not only interested in mapping one formalism into another, but also in ex- ploring the relationship between concepts employed in the two frameworks. HPSG is a feature-based grammatical framework which is characterized by a modular specification of linguistic generalizations through extensive use of principles and lexicalization of grammatical informa- tion. Traditional grammar rules are generalized to schemata providing an abstract definition of gram- matical relations, such as head-of, complement-of, subject-of, adjunct-of, etc. Principles, such as the *We would like to thank A. Abeill6, D. Flickinger, A. Joshi, T. Kroch, O. Rambow, I. Sag and H. Uszko- reit for valuable comments and discussions. The reseaxch underlying the paper was supported by research grants from the German Bundesministerium fiir Bildung, Wis- senschaft, Forschung und Technologie (BMBF) to the DFKI projects DIsco, FKZ ITW 9002 0, PARADICE, FKZ ITW 9403 and the VERBMOB1L project, FKZ 01 IV 101 K/l, and by the Center for Cognitive Science at Ohio State University. Head-Feature-, Valence-, Non-Local- or Semantics- Principle, determine the projection of information from the lexicon and recursively define the flow of information in a global structure. Through this modular design, grammatical descriptions are bro- ken down into minimal structural units referring to local trees of depth one, jointly constraining the set of well-formed sentences. In HPSG, based on the concept of "head- domains", local relations (such as complement-of, adjunct-of) are defined as those that are realized within the domain defined by the syntactic head. This domain is usually the maximal projection of the head, but it may be further extended in some cas- es, such as raising constructions. In contrast, filler- gap relations are considered non-local. This local vs. non-local distinction in HPSG cuts across the relations that are localized in TAG via the domains defined by elementary trees. Each elementary tree typically represents all of the arguments that are dependent on a lexical functor. For example, the complement-of and filler-gap relations are localized in …

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