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<Paper uid="P01-1007">
  <Title>Guided Parsing of Range Concatenation Languages</Title>
  <Section position="2" start_page="0" end_page="0" type="intro">
    <SectionTitle>
1 Introduction
</SectionTitle>
    <Paragraph position="0"> Usually, during a nondeterministic process, when a nondeterministic choice occurs, one explores all possible ways, either in parallel or one after the other, using a backtracking mechanism. In both cases, the nondeterministic process may be assisted by another process to which it asks its way.</Paragraph>
    <Paragraph position="1"> This assistant may be either a guide or an oracle.</Paragraph>
    <Paragraph position="2"> An oracle always indicates all the good ways that will eventually lead to success, and those good ways only, while a guide will indicate all the good ways but may also indicate some wrong ways. In other words, an oracle is a perfect guide (Kay, 2000), and the worst guide indicates all possible ways. Given two problems a12a14a13 and a12a16a15 and their respective solutions a17a18a13 and a17a19a15 , if they are such that a17a20a13a22a21a23a17a8a15 , any algorithm which solves a12 a13 is a candidate guide for nondeterministic algorithms solving a12a16a15 . Obviously, supplementary conditions have to be fulfilled fora12a24a13 to be a guide. The first one deals with relative efficiency: it assumes that problem a12a24a13 can be solved more efficiently than problem a12 a15 . Of course, parsers are privileged candidates to be guided. In this paper we apply this technique to the parsing of a subset of RCLs that are the languages defined by RCGs. The syntactic formalism of RCGs is powerful while staying computationally tractable. Indeed, the positive version of RCGs [PRCGs] defines positive RCLs [PRCLs] that exactly cover the class PTIME of languages recognizable in deterministic polynomial time. For example, any mildly context-sensitive language is a PRCL.</Paragraph>
    <Paragraph position="3"> In Section 2, we present the definitions of PRCGs and PRCLs. Then, in Section 3, we design an algorithm which transforms any PRCLa11 into another PRCLa11a25a13,a11a27a26a28a11a29a13 such that the (theoretical) parse time for a11a29a13 is less than or equal to the parse time fora11 : the parser fora11 will be guided by the parser for a11a29a13 . Last, in Section 4, we relate some experiments with a wide coverage tree-adjoining grammar [TAG] for English.</Paragraph>
  </Section>
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