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<Paper uid="P92-1011">
  <Title>COMPARING TWO GRAMMAR-BASED GENERATION A CASE STUDY</Title>
  <Section position="3" start_page="0" end_page="0" type="intro">
    <SectionTitle>
1. INTRODUCTION
</SectionTitle>
    <Paragraph position="0"> Recently, two important new algorithms have been published (\[SNMP89\], \[SNMP90\], \[S90a\], \[S90b\] and \[$91\]) that address the problem of automated generation of natural language expressions from a structured representation of meaning. Both algorithms follow the same general principle: given a grammar, and a structured representation of meaning, produce one or more corresponding surface strings, and do so with a minimal possible effort. In this paper we limit our analysis of the two algorithms to unification-based formalisms.</Paragraph>
    <Paragraph position="1"> The first algorithm, which we call here the Semantic-Head-Driven Generation Algorithm (SHDGA), uses information about semantic heads ~ in grammar rules to obtain the best possible traversal of the generation tree, using a mixed top-down/bottom-up strategy.</Paragraph>
    <Paragraph position="2"> The semantic head of a rule is the literal on the right-hand side that shares the semantics with the literal on the left. The second algorithm, which we call the Essential Arguments Algorithm (EAA), rearranges grammar productions at compile time in such a way that a simple top-down left-to-right evaluation will follow an optimal path.</Paragraph>
    <Paragraph position="3"> Both algorithms have resolved several outstanding problems in dealing with natural language grammars, including handling of left recursive rules, non-monotonic compositionality of representation, and deadlock-prone rules 2. In this paper we attempt to compare these two algorithms along their generality and efficiency lines. Throughout this paper we follow the notation used in \[SNMP90\].</Paragraph>
  </Section>
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