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<!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 Vsnapshot" /><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 11.5 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>
Text search parsers are responsible for splitting raw document text
into <em class="firstterm">tokens</em> and identifying each token's type, where
the set of possible types is defined by the parser itself.
Note that a parser does not modify the text at all — it simply
identifies plausible word boundaries. Because of this limited scope,
there is less need for application-specific custom parsers than there is
for custom dictionaries. At present <span class="productname">PostgreSQL</span>
provides just one built-in parser, which has been found to be useful for a
wide range of applications.
</p><p>
The built-in parser is named <code class="literal">pg_catalog.default</code>.
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>.
</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>
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
<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"><a href="dictionaries.html"></code></td></tr><tr><td><code class="literal">entity</code></td><td>XML entity</td><td><code class="literal">&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>
The parser's notion of a <span class="quote">“<span class="quote">letter</span>”</span> is determined by the database's
locale setting, specifically <code class="varname">lc_ctype</code>. Words containing
only the basic ASCII letters are reported as a separate token type,
since it is sometimes useful to distinguish them. In most European
languages, token types <code class="literal">word</code> and <code class="literal">asciiword</code>
should be treated alike.
</p><p>
<code class="literal">email</code> does not support all valid email characters as
defined by RFC 5322. Specifically, the only non-alphanumeric
characters supported for email user names are period, dash, and
underscore.
</p></div><p>
It is possible for the parser to produce overlapping tokens from the same
piece of text. As an example, a hyphenated word will be reported both
as the entire word and as each component:
</p><pre class="screen">
SELECT alias, description, token FROM ts_debug('foo-bar-beta1');
alias | description | token
-----------------+------------------------------------------+---------------
numhword | Hyphenated word, letters and digits | foo-bar-beta1
hword_asciipart | Hyphenated word part, all ASCII | foo
blank | Space symbols | -
hword_asciipart | Hyphenated word part, all ASCII | bar
blank | Space symbols | -
hword_numpart | Hyphenated word part, letters and digits | beta1
</pre><p>
This behavior is desirable since it allows searches to work for both
the whole compound word and for components. Here is another
instructive example:
</p><pre class="screen">
SELECT alias, description, token FROM ts_debug('http://example.com/stuff/index.html');
alias | description | token
----------+---------------+------------------------------
protocol | Protocol head | http://
url | URL | example.com/stuff/index.html
host | Host | example.com
url_path | URL path | /stuff/index.html
</pre><p>
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