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<Paper uid="W05-1523">
  <Title>Parsing Generalized ID/LP Grammars</Title>
  <Section position="3" start_page="0" end_page="0" type="metho">
    <SectionTitle>
2 Defining GIDLP Grammars
</SectionTitle>
    <Paragraph position="0"> A brief overview of GIDLP syntax is given in 1, and an example GIDLP grammar is given in 2 that recognizes a very small fragment of German, focusing on the free word order of arguments and adjuncts in the Mittelfeld.1 The basic idea of this grammar is that no word order constraints apply below the level of the clause. This allows the verb's arguments and adjuncts to freely intermingle, before being compacted at the clause level, at which point the constraints on the location of the finite verb apply. It is important to note that this grammar cannot be straightforwardly expressed in the ID/LP formalism, where LP constraints only apply within local trees.</Paragraph>
  </Section>
  <Section position="4" start_page="0" end_page="192" type="metho">
    <SectionTitle>
3 The GIDLP Parsing Algorithm
</SectionTitle>
    <Paragraph position="0"> The GIDLP parser Daniels and Meurers (2004a); Daniels (2005) is based on Earley's algorithm for 1For compactness, categories are described in this example with prolog-style terms; the actual GIDLP syntax assumes feature structure categories.</Paragraph>
    <Paragraph position="2"> context-free parsing, suitably modified to handle discontinuous constituents.</Paragraph>
    <Paragraph position="3"> A central insight of the GIDLP parsing algorithm is that the same data structure used to describe the coverage of an edge can also encode restrictions on the parser's search space. This is done by adding two bitvectors to each edge: a negative mask (n-mask), which marks positions that must not be part of the edge, and a positive mask (p-mask), which marks positions that must be part of the edge. These masks are generated during the prediction phase and then tested during the completion phase using efficient bitvector operations. Compiling LP constraints into  bitmasks in this way allows the LP constraints to be integrated directly into the parser at a fundamental level. Instead of weeding out inappropriate parses in a cleanup phase, LP constraints in this parser can immediately block an edge from being added to the chart.</Paragraph>
  </Section>
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