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Some Italian sentences related to linguistic phenomena largely known and recently discussed by many computational linguists are discussed in the framework of AT:~. They offer certain difficulties which seem to suggest a substantial revision of the ATN formalism. The theoretical assumptions and an experimental implementation of such a revision are presented, together with examples. }:any related theoretical points such as some psyeholinguistic implications and the relationship between deterministic and non-deterministlc hypothesis are also briefly discussed. . | EXTENDED ACCESS TO THE LEFT CONTEXT IN AN ATN PARSER Irina Prodanof and Giacomo Ferrari Istituto di Linguistica Computazionale Via della Faggiola 32 1-56100 Pisa Italy ABSTRACT Some Italian sentences related to linguistic phenomena largely known and recently discussed by many computational linguists are discussed in the framework of ATN. They offer certain difficulties which seem to suggest a substantial revision of the ATN formalism. The theoretical assumptions and an experimental implementation of such a revision are presented together with examples. Many related theoretical points such as some psycholinguistic implications and the relationship between deterministic and non-Jeterministic hypothesis are also briefly discussed. I. INTRODUCTION Certain types of sentences seem to defy the abilities of several parsers and some of them are being now discussed by many computational linguists mostly within the deterministic hypothesis. An examination of their treatment within the traditional ATI paradigm seems to suggest that the real discussion is about how to acces the left context and what Its form should be. II. ACCESS TO THE LEFT CONTEXT A. ATM Grammars An ATM grammar is a set of networks formed by labelled states and directed arcs connecting them. The arcs can ricognize terminal words and non-terminal lexical categories symbols or recursively call for a network identified by the label of an initial state. When such a call occurs the parsing algorithm suspends the current computation and starts a new level of computation. Usually each network recognizes some linguistic unit such as Noun Phrase NP Prepositional Phrase pp and Sentence S and any recursively embedded call to one of them corresponds to a level of computation. The parsed parts of the input string are stored SETRed into registers as they are recognized. At the end of the network these registers are combined BUILDQed into a parse node and returned POPed to the calling net. Appropriate functions can return .
