Integrating Sehantics and Flexible Syntax by Exploiting Isomorphism Between Grammatical and Semantical Relations

T INTEGRATING SEMANTICS kNO FLEXIBLE SYNTAX BY EXPLOITING ISONORPHISM BETWEEN GRAIelATICAL AND SEMANTICAL RELATIONS Norena Danieli, Franco Ferrara, Roberto Gemello, C1audio Rullent CSELT - Centro Studi • Laboratori Telecoaunicezloni - Via G.Relss Roaoli 274, 10148 Torino, ITALY • ABSTRACT This work concerns integration between syntax and semantics. Syntactic and semantic activities rely on separate bodies of knowledges. Integration is obtained by exploiting the isomorphism between grammatical relations (among immediate constitu~ errs) and conceptual relations, thanks to a limited set of formal mapping rules. Syntactic analysis does not construct all the explicit parse trees but just a graph that represents all the plausible grammatical relations among immediate constituents. Such graph gives the semantic interpreter, based on Conceptual Graphs formalism, the discriminative power required to establish conceptual relations. I. INTRODUCTION In the field of automatic natural language understanding, the problem of connecting syntax and semantics has been faced in three different ways. Some authors are persuaded that understanding natural language requires no use of syntactic know- ledge. They claim that semantic representation can be built directly from the surface string, without the help of almost any syntactic source (1). Other authors proposed highly syntactic sys- tems, starting from the idea that the represen- tation of the syntactic structure is preliminary to the understanding process (2). While the work of this second group of resear- chers was concerned mainly with the understanding of individual sentences, the work of the partisans of semantics was about the understanding of whole texts. This shifting of attention substained the idea that syntax and semantics should be used in an integrated way. Most researchers have thought that semantics and syntax should be integrated with respect to both the representation and the pro- cessing (3); others have claimed that it is more efficient to build a full-blooded syntactic repre- sentation during the parsing process (4). (1) See the system IPP [Schank 80]. (2) The LUNAR system [Woods ?2] is a classical example. (3) An example is the Conceptual Analyzer [Birnbaum 81]. (4) See MOPTRANS [Lytinen 85], Our approach shares some communalities with the last position. We reckon that semantic and syntac- tic processes should rely on separate knowledge bodies. Uur effort is mainly focused on the reali- zation of the integration by exploiting the iso- morphism between syntactic structures and semantic representations, rather than by making syntactic and semantic processes interact, as it happens in previous integrated parsers (5). The idea of iso- morphism is not carried out through one-to-one cor- respondence between syntactic rules and semantic ones - as in Montague-inspired parsers (6), but by mapping in a formal way grammatical and conceptual relations. The use of grammatical relations as in- termediate level between syntax and semantics was also adopted in the KING KONG parser (7), but this system is still more near to the position which wants the representation of syntax and semantics as well as their processes to interact, while our choice is to maintain separate these different sources of knowledge. The subsequent paragraphs describe how …

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