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<Paper uid="P84-1114">
  <Title>INTERPRETING SYNTACTICALLY ILL-FORMED SENTENCES</Title>
  <Section position="3" start_page="0" end_page="0" type="intro">
    <SectionTitle>
INTRODUCTION
</SectionTitle>
    <Paragraph position="0"> In the last years we have been involved in building a natural language (Italian) interface to ward a relational database. Even if this research required to consider issues relative to knowledge representation (Lesmo et al 83) and query optimiza tion (Lesmo et al, in press), our main concern was to devise efficient parsing techniques (Lesmo et al 81, Lesmo &amp; Torasso 83).</Paragraph>
    <Paragraph position="1"> The term &amp;quot;efficient&amp;quot;, when applied to language processing, can take a number of different meanings, ranging from pure processing speed to the ability to analyze fragments of text, to the flexibility that characterizes the behavior of the parser. We believe that all facets of efficiency are worth be ing pursued, but if the communication between the man and the machine has to occur in a really natu ral fashion, the robustness of the parser, i.e. its ability to cope with unforeseen inputs must receive the greatest attention. It is important to realize that &amp;quot;unforeseen&amp;quot; is assumed her to refer to the syntactic form of the input sentence: of course, also inputs that are unexpected from a semantic point of view should be handled properly, but, since usually the syntactic knowledge acts as a fil ter between the reception of the input and the sub sequent stages of the analysis, the first problem that must be faced is the following: how can the parser be prevented from rejecting sentences that are syntactically ill-formed, but could be interpr_e ted correctly if they are passed to the other comp2 nents of the system? Alternatively, the problem can be stated as: how to foresee every interpretable input? Marcus (1982) envisages the following alternatives: a) the use of special &amp;quot;un-grammatical&amp;quot; rules, which explicitly encode facts about non-standard usage b) the use of &amp;quot;meta-rules&amp;quot; to relax the constraints imposed by classes of rules of the grammar c) allowing flexible interaction between syntax and semantics, so that semantics can directly ana lyze substrings of syntactic fragments or indi vidual words when full syntactic analysis fails.</Paragraph>
    <Paragraph position="2"> Even if we agree in stating the importance of a strong interaction between syntax and semantics, our approach is quite different from c) (as well as from the other ones). For this reason, and in spite of the fact that a detailed description of the parser's operating principles has been given elsewhere (Lesmo &amp; Torasso 83), the next section is devoted to an introduction to the basic ideas that led to the design of the syntactic knowledge source.</Paragraph>
    <Paragraph position="3"> The subsequent sections will cover some phenomena which are related with ill-formedness of sentences, namely: ellipsis, conjunctions, and some types of actual syntactic errors.</Paragraph>
  </Section>
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