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Green_GoodERP18_FSJ_Standard/PostgreSQL/doc/postgresql/html/textsearch-parsers.html

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  1. <?xml version="1.0" encoding="UTF-8" standalone="no"?>

  2. <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>12.5. Parsers</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets V1.79.1" /><link rel="prev" href="textsearch-features.html" title="12.4. Additional Features" /><link rel="next" href="textsearch-dictionaries.html" title="12.6. Dictionaries" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">12.5. Parsers</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="textsearch-features.html" title="12.4. Additional Features">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="textsearch.html" title="Chapter 12. Full Text Search">Up</a></td><th width="60%" align="center">Chapter 12. Full Text Search</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 12.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="textsearch-dictionaries.html" title="12.6. Dictionaries">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="TEXTSEARCH-PARSERS"><div class="titlepage"><div><div><h2 class="title" style="clear: both">12.5. Parsers</h2></div></div></div><p>

  3.    Text search parsers are responsible for splitting raw document text

  4.    into <em class="firstterm">tokens</em> and identifying each token's type, where

  5.    the set of possible types is defined by the parser itself.

  6.    Note that a parser does not modify the text at all — it simply

  7.    identifies plausible word boundaries.  Because of this limited scope,

  8.    there is less need for application-specific custom parsers than there is

  9.    for custom dictionaries.  At present <span class="productname">PostgreSQL</span>

  10.    provides just one built-in parser, which has been found to be useful for a

  11.    wide range of applications.

  12.   </p><p>

  13.    The built-in parser is named <code class="literal">pg_catalog.default</code>.

  14.    It recognizes 23 token types, shown in <a class="xref" href="textsearch-parsers.html#TEXTSEARCH-DEFAULT-PARSER" title="Table 12.1. Default Parser's Token Types">Table 12.1</a>.

  15.   </p><div class="table" id="TEXTSEARCH-DEFAULT-PARSER"><p class="title"><strong>Table 12.1. Default Parser's Token Types</strong></p><div class="table-contents"><table class="table" summary="Default Parser's Token Types" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Alias</th><th>Description</th><th>Example</th></tr></thead><tbody><tr><td><code class="literal">asciiword</code></td><td>Word, all ASCII letters</td><td><code class="literal">elephant</code></td></tr><tr><td><code class="literal">word</code></td><td>Word, all letters</td><td><code class="literal">mañana</code></td></tr><tr><td><code class="literal">numword</code></td><td>Word, letters and digits</td><td><code class="literal">beta1</code></td></tr><tr><td><code class="literal">asciihword</code></td><td>Hyphenated word, all ASCII</td><td><code class="literal">up-to-date</code></td></tr><tr><td><code class="literal">hword</code></td><td>Hyphenated word, all letters</td><td><code class="literal">lógico-matemática</code></td></tr><tr><td><code class="literal">numhword</code></td><td>Hyphenated word, letters and digits</td><td><code class="literal">postgresql-beta1</code></td></tr><tr><td><code class="literal">hword_asciipart</code></td><td>Hyphenated word part, all ASCII</td><td><code class="literal">postgresql</code> in the context <code class="literal">postgresql-beta1</code></td></tr><tr><td><code class="literal">hword_part</code></td><td>Hyphenated word part, all letters</td><td><code class="literal">lógico</code> or <code class="literal">matemática</code>

  16.        in the context <code class="literal">lógico-matemática</code></td></tr><tr><td><code class="literal">hword_numpart</code></td><td>Hyphenated word part, letters and digits</td><td><code class="literal">beta1</code> in the context

  17.        <code class="literal">postgresql-beta1</code></td></tr><tr><td><code class="literal">email</code></td><td>Email address</td><td><code class="literal">foo@example.com</code></td></tr><tr><td><code class="literal">protocol</code></td><td>Protocol head</td><td><code class="literal">http://</code></td></tr><tr><td><code class="literal">url</code></td><td>URL</td><td><code class="literal">example.com/stuff/index.html</code></td></tr><tr><td><code class="literal">host</code></td><td>Host</td><td><code class="literal">example.com</code></td></tr><tr><td><code class="literal">url_path</code></td><td>URL path</td><td><code class="literal">/stuff/index.html</code>, in the context of a URL</td></tr><tr><td><code class="literal">file</code></td><td>File or path name</td><td><code class="literal">/usr/local/foo.txt</code>, if not within a URL</td></tr><tr><td><code class="literal">sfloat</code></td><td>Scientific notation</td><td><code class="literal">-1.234e56</code></td></tr><tr><td><code class="literal">float</code></td><td>Decimal notation</td><td><code class="literal">-1.234</code></td></tr><tr><td><code class="literal">int</code></td><td>Signed integer</td><td><code class="literal">-1234</code></td></tr><tr><td><code class="literal">uint</code></td><td>Unsigned integer</td><td><code class="literal">1234</code></td></tr><tr><td><code class="literal">version</code></td><td>Version number</td><td><code class="literal">8.3.0</code></td></tr><tr><td><code class="literal">tag</code></td><td>XML tag</td><td><code class="literal">&lt;a href="dictionaries.html"&gt;</code></td></tr><tr><td><code class="literal">entity</code></td><td>XML entity</td><td><code class="literal">&amp;amp;</code></td></tr><tr><td><code class="literal">blank</code></td><td>Space symbols</td><td>(any whitespace or punctuation not otherwise recognized)</td></tr></tbody></table></div></div><br class="table-break" /><div class="note"><h3 class="title">Note</h3><p>

  18.     The parser's notion of a <span class="quote">“<span class="quote">letter</span>”</span> is determined by the database's

  19.     locale setting, specifically <code class="varname">lc_ctype</code>.  Words containing

  20.     only the basic ASCII letters are reported as a separate token type,

  21.     since it is sometimes useful to distinguish them.  In most European

  22.     languages, token types <code class="literal">word</code> and <code class="literal">asciiword</code>

  23.     should be treated alike.

  24.    </p><p>

  25.     <code class="literal">email</code> does not support all valid email characters as

  26.     defined by RFC 5322.  Specifically, the only non-alphanumeric

  27.     characters supported for email user names are period, dash, and

  28.     underscore.

  29.    </p></div><p>

  30.    It is possible for the parser to produce overlapping tokens from the same

  31.    piece of text.  As an example, a hyphenated word will be reported both

  32.    as the entire word and as each component:

  33. 

  34. </p><pre class="screen">

  35. SELECT alias, description, token FROM ts_debug('foo-bar-beta1');

  36.       alias      |               description                |     token     

  37. -----------------+------------------------------------------+---------------

  38.  numhword        | Hyphenated word, letters and digits      | foo-bar-beta1

  39.  hword_asciipart | Hyphenated word part, all ASCII          | foo

  40.  blank           | Space symbols                            | -

  41.  hword_asciipart | Hyphenated word part, all ASCII          | bar

  42.  blank           | Space symbols                            | -

  43.  hword_numpart   | Hyphenated word part, letters and digits | beta1

  44. </pre><p>

  45. 

  46.    This behavior is desirable since it allows searches to work for both

  47.    the whole compound word and for components.  Here is another

  48.    instructive example:

  49. 

  50. </p><pre class="screen">

  51. SELECT alias, description, token FROM ts_debug('http://example.com/stuff/index.html');

  52.   alias   |  description  |            token             

  53. ----------+---------------+------------------------------

  54.  protocol | Protocol head | http://

  55.  url      | URL           | example.com/stuff/index.html

  56.  host     | Host          | example.com

  57.  url_path | URL path      | /stuff/index.html

  58. </pre><p>

  59.   </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="textsearch-features.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="textsearch.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="textsearch-dictionaries.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">12.4. Additional Features </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 12.6. Dictionaries</td></tr></table></div></body></html>
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