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<Paper uid="P85-1032">
  <Title>Structure-Sharing in Lexical Representation</Title>
  <Section position="7" start_page="265" end_page="266" type="concl">
    <SectionTitle>
4. Conclusion
</SectionTitle>
    <Paragraph position="0"> Having sketched the mechanisms employed in reducing redundant specification in the lexicon for the HPSG system, and having indicated the brevity of the grammar which results from our rich lexicon, we now summarize the advantages we see in representing the lexicon as we do, apart from the obvious advantage of a much smaller grammar. These advantages have to do in large part with the rigors of developing a large natural language system, but correspond at several points to concerns in theoretical linguistics as well.</Paragraph>
    <Paragraph position="1"> First axe a set of advantages that derive from being able to make a single substitution or addition which will effect a desired change throughout the system. This ability obviously eases the task of development based on experimentation, since one can quickly try several minor variations of, say, feature combinations and accu- null rarely judge the result on the overall system. Of equal importance to development is the consistency provided, given that one can make a modification to, say, the features for plural nouns, and be sure that all regular nouns will reflect the change consistently. Third, we can handle many additions to the lexicon by users without requiring expertise of the user in getting all the particular details of a lexical entry right, for an important (though far from complete) range of cases. Note that this ability to handle innovations seems to have a close parallel in people's ability to predict regular inflected forms for a word never before encountered.</Paragraph>
    <Paragraph position="2"> A second advantage that comes largely for free given the inheritance mechanisms we employ involves the phenomenon referred to as blocking II, where the existence of an irregular form of a word precludes the application of a lexical rule which would otherwise produce the corresponding regular form. By allowing individual lexical entries to turn off the relevant lexical rules based on the presence in the ,frame of an irregular form, we avoid producing, say, the regular past tense form =maked, since as we saw, the entry for make warns explicitly of an irregular spelling for the past tense form.</Paragraph>
    <Paragraph position="3"> Already mentioned above was a third advantage of using the mechanisms we do, namely that we can use inheritance to help us specify quite precisely the domain of a particular lexical rule, rather than having to try every lexical rule on every new frame only to discover that in most cases the rule fails to apply.</Paragraph>
    <Paragraph position="4"> Finally, we derive an intriguing benefit from having the ability to create on-the-fly noun frames for anydatabase entry, and from our decision to store our lexical items using the same representation language that is used for the target database: we are able without additional effort to answer queries about the make-up of the natural language system itself. That is, we can get an accurate answer to a question like How many verbs are there? in exactly the way that we answer the question IIom many managers are there ?. This ability of our system to reflect upon its own structure may prove to be much more than a curiosity as the system continues to grow; it may well become an essential tool for the continued development of the system itself. The potential for usefulness of this reflective property is enhanced by the fact that we now also represent our grammar and several other data structures for the system in this same frame representation language, and may progress to representing in frames other intermediate stages of the processing of a sentence. This enhanced ability to extend the lexicai coverage of our system frees us to invest more effort in meeting the many other challenges of developing a practical, extensible implementation of a natural language system embedded in a aerious linguistic theory.</Paragraph>
  </Section>
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