A Semantic Interpreter for Systemic Grammars

A :SEMANTIC INTERPRETER FOR SYSTEMIC GRAMMARS Tim F. O'Donoghue t immy@uk, ac. leeds, ai Division of Artificial Intelligence School of Computer Studies The University of Leeds Leeds LS2 9JT. UK +44 532 33.5430 ABSTRACT This paper describes a method for obtaining the semantic representation for a syntax tree in Sys- temic Grammar (SG). A prototype implementation of this method -- the REVELATION1 semantic inter- preter -- has been ldeveloped. It is derived from a SG generator foe a large subset of English -- GENESYS -- and is !thus, in contrast with most re- versible grammars, fan interpreter based on a gen- erator. A task decomposition approach is adopted for this reversal process which operates within the framework of SG, thus demonstrating that Systemic Grammars can be reversed and hence that a SG is a truly bi-directional formalism, p Introduction SG (see Butler [4] for a good introduction) is a useful model of lan~guage, having found many ap- plications in the areas of stylistics, text analy- sis, educational linggistics and artificial intelligence. Some of these applications have been colnputa- tional, the best known probably being Winograd's SHRDLU [22]. Howdver, most computational appli- cations have been designed from a text-generation viewpoint (such as Davey's PROTEUS [6], Manta and Matthiessen's NmEL [16, 17] and Fawcett and rlhtcker's ¢ENESYS [!0]). Because of this text-generation viewpoint of sys- ten tic grammarians, the mechanism for sentence analysis within SG (the reverse of the sentence gen- eration process) h~ received much less attention. This paper describes one stage of the sentence anal- ysis process: semantic interpretation.l 1 This assumes that Isentence analysis can be decomposed into two processes: syntactic analysis (parsing) plus semantic In Fawcett's SG, 2 a syntax tree (whose leaves de- fine a sentence) is generated from a set of semantic choices. R.EVELATION1 reverses this process: it at- tempts to find the set of semantic choices needed to generate a given syntax tree. In sentence gener- ation, a tree is generated, but only the leaves (the words) are 'output', the rest of the tree is simply deleted. In tile reverse process, when a sentence is input, a syntax tree must first be found before it can be interpreted. REVELATION1 assumes that a sepa- rate SG parser (not discussed here) is available; for an example of such a parser see O'Donoghue [20]. Thus REVELATION1 directly mirrors the generator, while the parser mirrors tlle tree deletion process. REVELATION1 has been developed within the PoPI.OG environment, a It is coded in a com- bination of PoPll [1] and Prolog [5] and utilizes GENESYS. GENESYS is a very large SG generator for English, written in Prolog (Fawcett and Tucker [10]) and it is version PG1.5 that has been used for the de- velopment and testing of REVELATIONI. GENESYS and REVELATION are part of a much larger project, the COMMUNAL 4 Project, the aim of which is to build a natural language interface to a rich SG oriented IKBS in tim domain of personnel manage- interp|~etation. These processes are not …

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