Generalized Memory Manipulating Actions for Parsing Natural Language

GENERALIZED MEMORY MANIPULATING ACTIONS FOR PARSING NATURAl. LANGUAGE lrina Prodanof Giacomo Fcrrari Istituto di Linguistica Computazionale Department of Linguistics CNR-Pisa Unwersity of Pisa Abstract Current (computational) linguistic theories have developed specific fos'malisllls for representing linguistic phenomena such as unbounded dependencies, relatives, etc, In this contribution we present a model el linguistic structures storing and accessing, which accounts for the same phenomena in a procedural way. Such a model has been implemented in the frame of an ATN parser. 1. Introduction Literature on parsing natural language has recently been concerned with topics which are unfamiliar to traditional Computational Linguistics such as functional similarities of different syntactic constructions (I), reanalysis of 'indelible' structures (9), manipulation of 'indelible' trees (7) Must of the linguistic problems involved are connected with unbounded dependencies and antecedent-referent binding. Grammatical formalisms have been developed, which represent certain linguistic phenomena in terms of discontinuous constituents (10), or generate unboundedly dependent symbols on the basis of specific conventions (4,5l However, the corresponding parsing algorithms are simple modifications of traditional parsers, where the extentions of h)rmalisms are not adequately accounted for on the procedural side Our approach to the problem of parsing Natural Language is to identify a set of processing strategies which may not only process, but also represent the alluded phenomena within the frame of a psychologically motivated CF parsing algorithm, ~_. Generalized memory manipulating actions EXAM-LC (EXtondend Access and Manipulation of the Left Context) is a model of linguistic structures storing and accessing designed according to such a psychological procedural approach. It relies upon the following assumptions -. the left context, ie. the structure corresponding to the currently analyzed part of the input string, is often affected in some way by newly incoming information and may contain information which affect further analysis Therefore, it must be accessible beyond possible limits imposed by the structure of the parser. In fact, in many cases the data within the scope of the current constituent or rule are more freely accessible than the others. On the contrary, the scope of accessibility to the left context should be specified according to how far it is affected or affects the current analysis; -a set of general actions can be defined corresponding to mental operations actually accomplished during the process of comprehension. Any surface construction is described both by its (deep) representation and by the operations which perform the mapping These actions can be assumed as linguistic procedural universals: -. it is possible that syntactic phenomena, that have different structural explications, are handled by a common process or sequence of operations A common space of memory is assumed to contain the current hypothesis about the analysis of the parsed segment of the input from the beginning We will refer to such a structured space as Current Global ]lypethesis (CGH) The following set of abstract operations on the space of memory has been defined till now a) an opening and a closing action wsll respectively start and end the storing of the information related to a …

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