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<title>RECOLL: a personal text search system for
Unix/Linux</title>
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<meta name="Author" content="Jean-Francois Dockes">
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"recoll is a simple full-text search system for unix and linux based on the powerful and mature xapian engine">
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"full text search,fulltext,desktop search,unix,linux,solaris,open source,free">
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<h1 class="intro">Recoll features</h1>
<dl>
<dt><a name="systems">Supported systems</a></dt>
<dd><span class="application">Recoll</span> has been compiled and
tested on FreeBSD, Linux, Darwin and Solaris (versions
FreeBSD 5.5, Redhat 7.3, Fedora Core 5, Suse 10.1, Gentoo,
Debian 3.1, Solaris 8/9, but other not too distant releases
should be ok too). You can download the source code and some
precompiled packages <a href="download.html">here</a>.</dd>
<dd>Qt versions from 3.1</dd>
<dt><a name="doctypes">Document types</a></dt>
<dd>Supports the following document types (along with their
compressed versions):
<dl>
<dt>Natively</dt>
<dd>
<ul>
<li><var class="literal">text</var>.</li>
<li><var class="literal">html</var>.</li>
<li><span class="application">OpenOffice</span>
files (needs <b>unzip</b> command).</li>
<li><var class="literal">maildir</var> and <var
class="literal">mailbox</var> (<span class=
"application">Mozilla</span>, <span class=
"application">Thunderbird</span> and <span class=
"application">Evolution</span> mail ok).</li>
<li><span class="application">gaim</span> log files.</li>
</ul>
</dd>
<dt>With external helpers</dt>
<dd>
<ul>
<li><var class="literal">pdf</var> with <a href=
"http://www.foolabs.com/xpdf/">xpdf</a>.</li>
<li><var class="literal">postscript</var> with <a
href=
"http://www.gnu.org/software/ghostscript/ghostscript.html">
ghostscript</a> and <a href=
"http://www.cs.wisc.edu/~ghost/doc/pstotext.htm">pstotext</a>.</li>
<li><var class="literal">msword</var> with <a href=
"http://www.winfield.demon.nl/">antiword</a>.</li>
<li><var class="literal">Powerpoint</var> and
<var class="literal">Excel</var> with the
<a href="http://www.45.free.net/~vitus/software/catdoc/">
catdoc</a> utilities.</li>
<li><var class="literal">rtf</var> with <a href=
"http://www.gnu.org/software/unrtf/unrtf.html">unrtf</a>.</li>
<li><var class="literal">dvi</var> with
<a href="http://www.radicaleye.com/dvips.html">dvips</a>.
</li>
<li><var class="literal">djvu</var> with
<a href="http://djvulibre.djvuzone.org/doc/index.html">DjVuLibre</a>.
</li>
<li><var class="literal">mp3</var> tags support with
<a href="http://id3lib.sourceforge.net/">id3info (id3lib)</a>.
</li>
</ul>
</dd>
</dl>
</dd>
<dt>Other features</dt>
<dd>
<ul>
<li>Multiple selectable databases.</li>
<li>Powerful query facilities, with boolean searches,
phrases, filter on file types and directory tree.</li>
<li>Specific file name searches with wildcards.</li>
<li>Support for multiple charsets. Internal processing and
storage uses Unicode UTF-8.</li>
<li><a href="#Stemming">Stemming</a> performed at query
time (can switch stemming language after indexing).</li>
<li>Easy installation. No database daemon, web server or
exotic language necessary.</li>
<li>An indexer which runs either as a thread inside the GUI
or as an external, cron'able program.</li>
</ul>
</dd>
</ul>
<h2><a name="#stemming"></a>Stemming</h2>
<p>Stemming is a process which transforms inflected words into
their most basic form. For exemple, <i>flooring</i>,
<i>floors</i>, <i>floored</i> would probably all be transformed
to <i>floor</i> by a stemmer for the English language.</p>
<p>In many search engines, the stemming process occurs during
indexing. The index will only contain the stemmed form of words,
with exceptions for terms which are detected as being probably
proper nouns (ie: capitalized). At query time, the terms entered
by the user are stemmed, then matched against the index.</p>
<p>This process results into a smaller index, but it has the
grave inconvenient of irrevocably losing information during
indexing.</p>
<p>Recoll works in a different way. No stemming is performed at
query time, so that all information gets into the index. The
resulting index is bigger, but most people probably don't care
much about this nowadays, because they have a 100Gb disk 95%
full of binary data <em>which does not get indexed</em>.</p>
<p>At the end of an indexing pass, Recoll builds one or several
stemming dictionaries, where all word stems are listed in
correspondence to the list of their derivatives.</p>
<p>At query time, by default, user-entered terms are stemmed,
then matched against the stem database, and the query is
expanded to include all derivatives. This will yield search
results analogous to those obtained by a classical engine.
The benefits of this approach is that stem expansion can be
controlled instantly at query time in several ways:
<ul>
<li>It can be selectively turned-off for any query term by
capitalizing it (<i>Floor</i>).</li>
<li>The stemming language (ie: english, french...) can be
selected (this supposes that several stemming databases have
been built, which can be configured as part of the indexing,
or done later, in a reasonably fast way).</li>
</ul>
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