The self-extending phrasal lexicon

  • Authors:
  • Uri Zernik;Michael G. Dyer

  • Affiliations:
  • General Electric, Schenectady NY;University of California, Los Angeles, California

  • Venue:
  • Computational Linguistics - Special issue of the lexicon
  • Year:
  • 1987

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Abstract

Lexical representation so far has not been extensively investigated in regard to language acquisition. Existing computational linguistic systems assume that text analysis and generation take place in conditions of complete lexical knowledge. That is, no unknown elements are encountered in processing text. It turns out however, that productive as well as non-productive word combinations require adequate consideration. Thus, assuming the existence of a complete lexicon at the outset is unrealistic, especially when considering such word combinations.Three new problems regarding the structure and the contents of the phrasal lexicon arise when considering the need for dynamic acquisition. First, when an unknown element is encountered in text, information must be extracted in spite of the existence of an unknown. Thus, generalized lexical patterns must be employed in forming an initial hypothesis, in absence of more specific patterns. Second, senses of single words and particles must be utilized in forming new phrases. Thus the lexicon must contain information about single words, which can then supply clues for phrasal pattern analysis and application. Third, semantic clues must be used in forming new syntactic patterns. Thus, lexical entries must appropriately integrate syntax and semantics.We have employed a Dynamic Hierarchical Phrasal Lexicon (DHPL) which has three features: (a) lexical entries are given as entire phrases and not as single words, (b) lexical entries are organized as a hierarchy by generality, and (c) there is not separate body of grammar rules: grammar is encoded within the lexical hierarchy. A language acquisition model, embodied by the program RINA, uses DHPL in acquiring new lexical entries from examples in context through a process of hypothesis formation and error correction. In this paper we show how the proposed lexicon supports language acquisition.