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<Paper uid="P01-1007">
  <Title>Guided Parsing of Range Concatenation Languages</Title>
  <Section position="6" start_page="0" end_page="0" type="concl">
    <SectionTitle>
7 Conclusion
</SectionTitle>
    <Paragraph position="0"> The experiment related in this paper shows that some kind of guiding technique has to be considered when one wants to increase parsing efficiency. With a wide coverage English TAG, on a small sample set of short sentences, a guided parser is on the average three times faster than its non-guided counterpart, while, for longer sentences, more than one order of magnitude may be expected.</Paragraph>
    <Paragraph position="1"> However, the guided parser speed is very sensitive to the level of the guide, which must be chosen very carefully since potential benefits may be overcome by the time taken by the guiding structure book-keeping procedures.</Paragraph>
    <Paragraph position="2"> Of course, the filtering principle related in this paper is not novel (see for example (Lakshmanan and Yim, 1991) for deductive databases) but, if we consider the various attempts of guided parsing reported in the literature, ours is one of the very few examples in which important savings are noted. One reason for that seems to be the extreme simplicity of the interface between the guiding and the guided process: the guide only performs a direct access into the guiding structure. Moreover, this guiding structure is (part of) the usual parse forest output by the guiding parser, without any transduction (see for example in (Nederhof, 1998) how a FSA can guide a CF parser).</Paragraph>
    <Paragraph position="3"> As already noted by many authors (see for example (Carroll, 1994)), the choice of a (parsing) algorithm, as far as its throughput is concerned, cannot rely only on its theoretical complexity but must also take into account practical experiments. Complexity analysis gives worst-case upper bounds which may well not be reached, and which implies constants that may have a preponderant effect on the typical size ranges of the application. null We have also noted that guiding parsers can be used in classical TAG parsers, as efficient and (very) accurate tree selectors. More generally, we are currently investigating the possibility to use guiding parsers as shallow parsers.</Paragraph>
    <Paragraph position="4"> The above results also show that (guided) RCL parsing is a valuable alternative to classical (lexicalized) TAG parsers since we have exhibited parse time savings of several orders of magnitude over the most recent XTAG parser. These savings even allow to consider the parsing of medium size sentences with the English XTAG.</Paragraph>
    <Paragraph position="5"> The global parse time for TAGs might also be further improved using the transformation described in (Boullier, 1999) which, starting from any TAG, constructs an equivalent RCG that can be parsed ina2a4a3a6a5a8a7a10a9. However, this improvement is not definite, since, on typical input sentences, the increase in size of the resulting grammar may well ruin the expected practical benefits, as in the case of thea5 a187 -guiding parser processing short sentences.</Paragraph>
    <Paragraph position="6"> We must also note that a (guided) parser may also be used as a guide for a unification-based parser in which feature terms are evaluated (see the experiment related in (Barth'elemy et al., 2000)).</Paragraph>
    <Paragraph position="7"> Although the related practical experiments have been conducted on a TAG, this guide technique is not dedicated to TAGs, and the speed of all PRCL parsers may be thus increased. This pertains in particular to the parsing of all languages whose grammars can be translated into equivalent PRCGs -- MC-TAGs, LCFRS, . . .</Paragraph>
  </Section>
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