LFG System in Prolog

In order to design and maintain a latE? scale grammar, the formal system for representing syntactic knowledEe should be provided. Lexlcal Functional Grammar (LFG) [Kaplan, Bresnan 82] is a powerful formalism for that purpose, In this paper, the Prolog implementation of LFG system is described. Prolog provides a Eood tools for the implementation of LFG. LFG can be translated into DCG [Perelra,IIarren 80] and functional structures (f-structures) are generated durlnK the parsing process. I INTRODUCTIOr~ The fundamental purposes of syntactic analysis are to check the Eramnatlcallty and to clariDI the mapping between semantic structures and syntactic constituents. DCG provides tools for fulfillln 6 these purposes. But, due to the fact that the arbitrary 9rolog programs can be embedded into DCG rules, the grammar becomes too complicated to understand, debug and maintain. So, the develo~ent of the formal system to represent syntactic knowled~es is needed. The main concern is to define the appropriate set of the descriptive primitives used to represent the syntactic knowledges. LFG seems to be promising formalism from current llngulstlc theories which satisfies these requirements. LFG is adopted for our prelimlna~y version of the formal system and the Prolog implementation of LFG is described in this paper. ii SII:~.Z OVERVI~ OF LFG in this section, the simple overview of LF~ is described (See [Eaplan, Bresnan 82] for details). LFG is an e::tention of context free grammar (C~'G) and has two-levels of representation, i.e. c-structures (constituent structures) and f-~tructures (functional structures). A c-structure is generated by CFG and represents the surface uord and phrase configurations in a ~entence, and the f-structure is generated by the functional equations a=sociated with the o~rammar rules and represents the conflo~uratlon of the surface ~ra=matical functions. Fi~. I shows the c-structure and f-structure for the sentence "a e~f.rl handed the baby a toy" ([Kaplan,Bresnan 82]).