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Processing Dictionary Definitions with Phrasal Pattern Hierarchies

Summary

Language understanding systems often break down when they meet words missing from their lexicons, or sentences their grammars cannot fully parse. Alshawi treats both as cases of incomplete linguistic knowledge. He builds an analyser that extracts classification-oriented semantic information from word sense definitions in the machine-readable Longman Dictionary of Contemporary English (LDOCE). The approach relies on the fact that LDOCE writes its definitions with a restricted vocabulary of about 2000 words. A new sense can therefore be placed within a hand-built classification of those vocabulary senses.

Analysis proceeds through a hierarchy of phrasal patterns. General patterns sit above more specialised ones, and matching moves downward as far as it succeeds. When a full analysis fails, a reasonable partial result still survives, most importantly the definition's semantic head (its main superordinate). The output is a nested feature list recording class, properties, purpose, parts and predications.

On a random sample of definitions, the system usually found the semantic head correctly. This suggests that cheap, robust pattern-based analysis can help NLP systems cope with unknown words.

Key points

  • Resource: LDOCE definitions were taken from a Lisp-converted version of the typesetting tape. The 2000-word defining vocabulary is closer to "basic English" than to a set of semantic primitives.
  • Evaluation: the test used 500 randomly selected definitions, excluding idioms and complex cross-references.
    • The semantic head was correct for 387 of them (77%).
    • Extra information was extracted for 236 of those (61%), and 207 of these extractions (88%) were judged correct.
  • Grammar size: the hierarchy holds about 90 phrasal patterns, including subsidiary ones. The author estimates it could grow to around 400 before returns diminish.
  • Implementation: the analyser is written in Cambridge Lisp, with dictionary access in C. It takes about half a second per definition on a GEC-63 minicomputer, and development took only a few person-months each for program and grammar.
  • Error sources and future work: most errors came from weak morphological analysis and limited pattern coverage. Proposed future work includes handling idioms as the most specific patterns at the leaves of the hierarchy.

Our summary of the paper, in our own words — not its text. The work belongs to its authors; read it at the links above.

Fields: Natural language processing

Institutions

🎓University of CambridgeCambridge · United Kingdom119 works · 110,950 citations

Cite

Cite as Hiyan Alshawi. 1987. Processing Dictionary Definitions with Phrasal Pattern Hierarchies. Computational Linguistics.

The paper itself, not this page. BibTeX from the library's record of the work.

@article{alshawi1987processing,
  title = {{Processing Dictionary Definitions with Phrasal Pattern Hierarchies}},
  author = {Hiyan Alshawi},
  journal = {Computational Linguistics},
  year = {1987},
  url = {https://aclanthology.org/J87-3001/}
}

References

20 references, 1 of them with a card of ours. ↗ leads to the work, «find» searches for one we have no id for yet.

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