On Interpreting F-Structures as UDRSs

On Interpreting F-Structures as UDRSs Josef van Genabith School of Computer Applications Dublin City University Dublin 9 Ireland j osef@compapp, dcu. ie Richard Crouch Department of Computer Science University of Nottingham University Park Nottingham NG7 2RD, UK rsc@cs, nott. ac. uk Abstract We describe a method for interpreting ab- stract fiat syntactic representations, LFG f- structures, as underspecified semantic rep- resentations, here Underspecified Discourse Representation Structures (UDRSs). The method establishes a one-to-one correspon- dence between subsets of the LFG and UDRS formalisms. It provides a model theoretic interpretation and an inferen- tial component which operates directly on underspecified representations for f- structures through the translation images of f-structures as UDRSs. 1 Introduction Lexical Functional Grammar (LFG) f-structures (Kaplan and Bresnan, 1982; Dalrymple et al., 1995a) are attribute-value matrices representing high level syntactic information abstracting away from the par- ticulars of surface realization such as word order or inflection while capturing underlying generaliza- tions. Although f-structures are first and foremost syntactic representations they do encode some se- mantic information, namely basic predicate argu- ment structure in the semantic form value of the PRED attribute. Previous approaches to provid- ing semantic components for LFGs concentrated on providing schemas for relating (or translating) f- structures (in)to sets of disambiguated semantic rep- resentations which are then interpreted model the- oretically (Halvorsen, 1983; Halvorsen and Kaplan, 1988; Fenstad et al., 1987; Wedekind and Kaplan, 1993; Dalrymple et al., 1996). More recently, (Gen- abith and Crouch, 1996) presented a method for providing a direct and underspecified interpretation of f-structures by interpreting them as quasi-logical forms (QLFs) (Alshawi and Crouch, 1992). The ap- proach was prompted by striking structural similar- ities between f-structure ['PRED ~COACH ~ ] SUBJ NUM SG /SPEC EVERY PRED 'pick (T SUB J, T OBJ)' [PRED 'PLAYER'] L°B: iN'M s/ J LSPE¢ and QLF representations ?Scope : pick (t erm(+r, <hUm= sg, spec=every>, coach, ?Q, ?X), term (+g, <num=sg, spec=a>, player, ?P, ?R) ) both of which are fiat representations which allow underspecification of e.g. the scope of quantifica- tional NPs. In this companion paper we show that f-structures are just as easily interpretable as UDRSs (Reyle, 1993; Reyle, 1995): coach(x) layer(y) I pick(x,y) I We do this in terms of a translation function r from f-structures to UDRSs. The recursive part of the def- inition states that the translation of an f-structure is simply the union of the translation of its component parts: 'F1 71 ... T( PRED I-[(~ rl,...,l l~n) ) r, ..... T r.)) u u... u While there certainly is difference in approach and emphasis between f-structures, QLFs and UDRSs 402 the motivation foi" flat (underspecified) representa- tions in each case is computational. The details of the LFG and UDRT formalisms are described at length elsewhere: here we briefly present the very basics of the UDRS formalism; we define a language of wff-s (well-formed f-structures); we define a map- ping 7" from f-structures to UDRSs together with a reverse mapping r -1 and we show correctness with respect to …

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