Direct and Underspecified Interpretations of LFG f-structures

Direct and Underspecified Interpretations of LFG f-structures Josef van Genabith* Insitute for Natural Language Processing University of Stuttgart Azenbergstr. 12 D-70174 Stuttgart, I?'RG j osef@ims, uni-stuttgart, de Dick Crouch 1 SRI International 23 Millers Yard Mill Lane Cambridge CB2 ]RQ, UK re@cam, sri. tom Abstract We describe an approach to interpreting LFG f-structures (Kaplan & Bresnan, 1982) truth-conditionally as underspeci- fled quasi-logical forms. F-structures are either interpreted indirectly in terms of a homomorphic embedding into Quasi Logical Form (QLF) (Alshawi, 1992; Alshawi & Crouch, 1992; Cooper et al., 1994a) representations or directly in terms of adapting QLF interpreta- tion clauses to f-structure representa- tions. We provide a reverse mapping from QLFs to f-structures and establish isomorphic subsets of the QLF and LFG formalism. A simple maI)ping which switches off QLF contextual resolution can be shown to be truth preserving with respect to an independently given se- mantics (Dalrymple et al., 1995). We compare our proposal with approaches discussed in the literature. 1 Introduction Ditferent languages express grammatical flmctions (such as subject or object) in a variety of ways, e.g. by position or by inflection. Functional-structures (f-structures) (Kaplan & Bresnan, 1982) are attribute-value matrices that provide a syntactic level of representation that is intended to abstract away from such surface variations while capturing what are considered underlying generalisations. Quasi-Logical Forms (QLFs) (Alshawi & Crouch, 1992; Cooper et al., 1994a) provide the seman- tic level of representation employed in the Core Language Engine (CLE) (Alshawi, 1992). The two main characteristics of the formalism are un- derspeeification and monotonic contextual reso- lution. QLFs give (partial) descriptions of in- *Present address: Dublin City University, Dublin 9, Ireland; josefOcompapp, dcu. ie l Present address: Speech Research Unit, DRA Malvern, St Andrews Road, Great Malvern, Worcs WR14 3PS, UK; croueh0signal, dra. hmg. gb tended semantic compositions. Contextual reso- lution monotonically adds to this description, e.g. by placing fln'ther constraints on the meanings of certain expressions like pronouns, or quanti- tier scope. QLFs at; all stages of resolution are interpreted by a truth-conditional semantics via a supervaluation construction over the composi- tions meeting the description. F-structures are a mixture of mostly syntactic information (gram- matical flmctions) with some semantic, predicate- argument information encoded via the values of PRED features: "PRED ~CANDIDATI,~ ~ NUM SG L OBJ LsPEc. A Unresolved QLF gives the basic predicate- argument structure of a sentence, mixed with some syntactic information encoded in the cate- gories of QLF terms and forms: 1 ?Scope : support (term (+r, <nmn=sg, spec=every>, representative, ?Q, ?X) , term (+g, <num=sg, spec=a>, candidate, ?P, ?R) ) While there is difference in approach and emphasis unresolved QLFs and f-structures bear a striking similarity and it ix easy to see how to get from one to the other: pn~:, n($ r~,.,? r,~> ~ .*Scope : n(~,.,~,~) £ ")% The core of a mapping taking us from fstructures to QLFs places the values of subcategorizable grammmatieal fnnctions into their argument posi- tions in the governing semantic form and recurses on those arguments. …

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