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<title>Xapian: API Documentation: xapian-core: Xapian::TradWeight Class Reference</title>
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<div class="navpath"><a class="el" href="namespaceXapian.html">Xapian</a>::<a class="el" href="classXapian_1_1TradWeight.html">TradWeight</a>
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<h1>Xapian::TradWeight Class Reference</h1><!-- doxytag: class="Xapian::TradWeight" --><!-- doxytag: inherits="Xapian::Weight" --><a class="el" href="classXapian_1_1Weight.html" title="Abstract base class for weighting schemes.">Xapian::Weight</a> subclass implementing the traditional probabilistic formula.
<a href="#_details">More...</a>
<p>
<div class="dynheader">
Inheritance diagram for Xapian::TradWeight:</div>
<div class="dynsection">
<p><center><img src="classXapian_1_1TradWeight__inherit__graph.png" border="0" usemap="#Xapian_1_1TradWeight__inherit__map" alt="Inheritance graph"></center>
<map name="Xapian_1_1TradWeight__inherit__map">
<area shape="rect" href="classXapian_1_1Weight.html" title="Abstract base class for weighting schemes." alt="" coords="17,7,132,33"></map>
<center><font size="2">[<a href="graph_legend.html">legend</a>]</font></center></div>
<p>
<a href="classXapian_1_1TradWeight-members.html">List of all members.</a><table border="0" cellpadding="0" cellspacing="0">
<tr><td></td></tr>
<tr><td colspan="2"><br><h2>Public Member Functions</h2></td></tr>
<tr><td class="memItemLeft" nowrap align="right" valign="top"> </td><td class="memItemRight" valign="bottom"><a class="el" href="classXapian_1_1TradWeight.html#904914c46534a32c666a473c9ffdf77c">TradWeight</a> (double k=1.0)</td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Construct a <a class="el" href="classXapian_1_1TradWeight.html" title="Xapian::Weight subclass implementing the traditional probabilistic formula.">TradWeight</a>. <a href="#904914c46534a32c666a473c9ffdf77c"></a><br></td></tr>
<tr><td class="memItemLeft" nowrap align="right" valign="top">std::string </td><td class="memItemRight" valign="bottom"><a class="el" href="classXapian_1_1TradWeight.html#a34538148bb8a2771675117d7331aee1">name</a> () const </td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Return the name of this weighting scheme. <a href="#a34538148bb8a2771675117d7331aee1"></a><br></td></tr>
<tr><td class="memItemLeft" nowrap align="right" valign="top">std::string </td><td class="memItemRight" valign="bottom"><a class="el" href="classXapian_1_1TradWeight.html#3cb90ec9c8ef2866dfa405d3490d4cc3">serialise</a> () const </td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Return this object's parameters serialised as a single string. <a href="#3cb90ec9c8ef2866dfa405d3490d4cc3"></a><br></td></tr>
<tr><td class="memItemLeft" nowrap align="right" valign="top"><a class="el" href="classXapian_1_1TradWeight.html">TradWeight</a> * </td><td class="memItemRight" valign="bottom"><a class="el" href="classXapian_1_1TradWeight.html#ce5aae016fc57407c7f7f5f0f3d7b5c0">unserialise</a> (const std::string &s) const </td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Unserialise parameters. <a href="#ce5aae016fc57407c7f7f5f0f3d7b5c0"></a><br></td></tr>
<tr><td class="memItemLeft" nowrap align="right" valign="top"><a class="el" href="namespaceXapian.html#cac12803afc9e24ee5141c119acb8884">Xapian::weight</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="classXapian_1_1TradWeight.html#fd3432ac3e0adab5b7c4ad61d2ced18d">get_sumpart</a> (<a class="el" href="namespaceXapian.html#72b5a76dd8cfb7b251fe7986e86390cb">Xapian::termcount</a> wdf, <a class="el" href="namespaceXapian.html#72b5a76dd8cfb7b251fe7986e86390cb">Xapian::termcount</a> doclen) const </td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Calculate the weight contribution for this object's term to a document. <a href="#fd3432ac3e0adab5b7c4ad61d2ced18d"></a><br></td></tr>
<tr><td class="memItemLeft" nowrap align="right" valign="top"><a class="el" href="namespaceXapian.html#cac12803afc9e24ee5141c119acb8884">Xapian::weight</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="classXapian_1_1TradWeight.html#bc2fd38d6abbb7ef77b14959ae3f1fc0">get_maxpart</a> () const </td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Return an upper bound on what <a class="el" href="classXapian_1_1TradWeight.html#fd3432ac3e0adab5b7c4ad61d2ced18d" title="Calculate the weight contribution for this object's term to a document.">get_sumpart()</a> can return for any document. <a href="#bc2fd38d6abbb7ef77b14959ae3f1fc0"></a><br></td></tr>
<tr><td class="memItemLeft" nowrap align="right" valign="top"><a class="el" href="namespaceXapian.html#cac12803afc9e24ee5141c119acb8884">Xapian::weight</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="classXapian_1_1TradWeight.html#c6f5746b1117b331a42e1bdc4002d65e">get_sumextra</a> (<a class="el" href="namespaceXapian.html#72b5a76dd8cfb7b251fe7986e86390cb">Xapian::termcount</a> doclen) const </td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Calculate the term-independent weight component for a document. <a href="#c6f5746b1117b331a42e1bdc4002d65e"></a><br></td></tr>
<tr><td class="memItemLeft" nowrap align="right" valign="top"><a class="el" href="namespaceXapian.html#cac12803afc9e24ee5141c119acb8884">Xapian::weight</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="classXapian_1_1TradWeight.html#5e06ecfe3f4ad59c4e1a651f604800e2">get_maxextra</a> () const </td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Return an upper bound on what <a class="el" href="classXapian_1_1TradWeight.html#c6f5746b1117b331a42e1bdc4002d65e" title="Calculate the term-independent weight component for a document.">get_sumextra()</a> can return for any document. <a href="#5e06ecfe3f4ad59c4e1a651f604800e2"></a><br></td></tr>
</table>
<hr><a name="_details"></a><h2>Detailed Description</h2>
<a class="el" href="classXapian_1_1Weight.html" title="Abstract base class for weighting schemes.">Xapian::Weight</a> subclass implementing the traditional probabilistic formula.
<p>
This class implements the "traditional" Probabilistic Weighting scheme, as described by the early papers on Probabilistic Retrieval. BM25 generally gives better results.<p>
TradWeight(k) is equivalent to BM25Weight(k, 0, 0, 1, 0), except that the latter returns weights (k+1) times larger. <hr><h2>Constructor & Destructor Documentation</h2>
<a class="anchor" name="904914c46534a32c666a473c9ffdf77c"></a><!-- doxytag: member="Xapian::TradWeight::TradWeight" ref="904914c46534a32c666a473c9ffdf77c" args="(double k=1.0)" -->
<div class="memitem">
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<td class="memname">Xapian::TradWeight::TradWeight </td>
<td>(</td>
<td class="paramtype">double </td>
<td class="paramname"> <em>k</em> = <code>1.0</code> </td>
<td> ) </td>
<td><code> [inline, explicit]</code></td>
</tr>
</table>
</div>
<div class="memdoc">
<p>
Construct a <a class="el" href="classXapian_1_1TradWeight.html" title="Xapian::Weight subclass implementing the traditional probabilistic formula.">TradWeight</a>.
<p>
<dl compact><dt><b>Parameters:</b></dt><dd>
<table border="0" cellspacing="2" cellpadding="0">
<tr><td valign="top"></td><td valign="top"><em>k</em> </td><td>A non-negative parameter controlling how influential within-document-frequency (wdf) and document length are. k=0 means that wdf and document length don't affect the weights. The larger k is, the more they do. (default 1) </td></tr>
</table>
</dl>
</div>
</div><p>
<hr><h2>Member Function Documentation</h2>
<a class="anchor" name="5e06ecfe3f4ad59c4e1a651f604800e2"></a><!-- doxytag: member="Xapian::TradWeight::get_maxextra" ref="5e06ecfe3f4ad59c4e1a651f604800e2" args="() const " -->
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<td class="memname"><a class="el" href="namespaceXapian.html#cac12803afc9e24ee5141c119acb8884">Xapian::weight</a> Xapian::TradWeight::get_maxextra </td>
<td>(</td>
<td class="paramname"> </td>
<td> ) </td>
<td> const<code> [virtual]</code></td>
</tr>
</table>
</div>
<div class="memdoc">
<p>
Return an upper bound on what <a class="el" href="classXapian_1_1TradWeight.html#c6f5746b1117b331a42e1bdc4002d65e" title="Calculate the term-independent weight component for a document.">get_sumextra()</a> can return for any document.
<p>
This information is used by the matcher to perform various optimisations, so strive to make the bound as tight as possible.
<p>Implements <a class="el" href="classXapian_1_1Weight.html#ca641ecc2f5645666820f864d243f46d">Xapian::Weight</a>.</p>
</div>
</div><p>
<a class="anchor" name="bc2fd38d6abbb7ef77b14959ae3f1fc0"></a><!-- doxytag: member="Xapian::TradWeight::get_maxpart" ref="bc2fd38d6abbb7ef77b14959ae3f1fc0" args="() const " -->
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<td class="memname"><a class="el" href="namespaceXapian.html#cac12803afc9e24ee5141c119acb8884">Xapian::weight</a> Xapian::TradWeight::get_maxpart </td>
<td>(</td>
<td class="paramname"> </td>
<td> ) </td>
<td> const<code> [virtual]</code></td>
</tr>
</table>
</div>
<div class="memdoc">
<p>
Return an upper bound on what <a class="el" href="classXapian_1_1TradWeight.html#fd3432ac3e0adab5b7c4ad61d2ced18d" title="Calculate the weight contribution for this object's term to a document.">get_sumpart()</a> can return for any document.
<p>
This information is used by the matcher to perform various optimisations, so strive to make the bound as tight as possible.
<p>Implements <a class="el" href="classXapian_1_1Weight.html#f37e797fa12bb915f73b20b953a132b7">Xapian::Weight</a>.</p>
</div>
</div><p>
<a class="anchor" name="c6f5746b1117b331a42e1bdc4002d65e"></a><!-- doxytag: member="Xapian::TradWeight::get_sumextra" ref="c6f5746b1117b331a42e1bdc4002d65e" args="(Xapian::termcount doclen) const " -->
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<td class="memname"><a class="el" href="namespaceXapian.html#cac12803afc9e24ee5141c119acb8884">Xapian::weight</a> Xapian::TradWeight::get_sumextra </td>
<td>(</td>
<td class="paramtype"><a class="el" href="namespaceXapian.html#72b5a76dd8cfb7b251fe7986e86390cb">Xapian::termcount</a> </td>
<td class="paramname"> <em>doclen</em> </td>
<td> ) </td>
<td> const<code> [virtual]</code></td>
</tr>
</table>
</div>
<div class="memdoc">
<p>
Calculate the term-independent weight component for a document.
<p>
The parameter gives information about the document which may be used in the calculations:<p>
<dl compact><dt><b>Parameters:</b></dt><dd>
<table border="0" cellspacing="2" cellpadding="0">
<tr><td valign="top"></td><td valign="top"><em>doclen</em> </td><td>The document's length (unnormalised). </td></tr>
</table>
</dl>
<p>Implements <a class="el" href="classXapian_1_1Weight.html#8c29b15b875e5666ac8b94c9a39e962f">Xapian::Weight</a>.</p>
</div>
</div><p>
<a class="anchor" name="fd3432ac3e0adab5b7c4ad61d2ced18d"></a><!-- doxytag: member="Xapian::TradWeight::get_sumpart" ref="fd3432ac3e0adab5b7c4ad61d2ced18d" args="(Xapian::termcount wdf, Xapian::termcount doclen) const " -->
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<td class="memname"><a class="el" href="namespaceXapian.html#cac12803afc9e24ee5141c119acb8884">Xapian::weight</a> Xapian::TradWeight::get_sumpart </td>
<td>(</td>
<td class="paramtype"><a class="el" href="namespaceXapian.html#72b5a76dd8cfb7b251fe7986e86390cb">Xapian::termcount</a> </td>
<td class="paramname"> <em>wdf</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype"><a class="el" href="namespaceXapian.html#72b5a76dd8cfb7b251fe7986e86390cb">Xapian::termcount</a> </td>
<td class="paramname"> <em>doclen</em></td><td> </td>
</tr>
<tr>
<td></td>
<td>)</td>
<td></td><td></td><td> const<code> [virtual]</code></td>
</tr>
</table>
</div>
<div class="memdoc">
<p>
Calculate the weight contribution for this object's term to a document.
<p>
The parameters give information about the document which may be used in the calculations:<p>
<dl compact><dt><b>Parameters:</b></dt><dd>
<table border="0" cellspacing="2" cellpadding="0">
<tr><td valign="top"></td><td valign="top"><em>wdf</em> </td><td>The within document frequency of the term in the document. </td></tr>
<tr><td valign="top"></td><td valign="top"><em>doclen</em> </td><td>The document's length (unnormalised). </td></tr>
</table>
</dl>
<p>Implements <a class="el" href="classXapian_1_1Weight.html#8c6beb18e2c08cbc2ae61ec9d808ed9e">Xapian::Weight</a>.</p>
</div>
</div><p>
<a class="anchor" name="a34538148bb8a2771675117d7331aee1"></a><!-- doxytag: member="Xapian::TradWeight::name" ref="a34538148bb8a2771675117d7331aee1" args="() const " -->
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<td class="memname">std::string Xapian::TradWeight::name </td>
<td>(</td>
<td class="paramname"> </td>
<td> ) </td>
<td> const<code> [virtual]</code></td>
</tr>
</table>
</div>
<div class="memdoc">
<p>
Return the name of this weighting scheme.
<p>
This name is used by the remote backend. It is passed along with the serialised parameters to the remote server so that it knows which class to create.<p>
Return the full namespace-qualified name of your class here - if your class is called FooWeight, return "FooWeight" from this method (<a class="el" href="classXapian_1_1BM25Weight.html" title="Xapian::Weight subclass implementing the BM25 probabilistic formula.">Xapian::BM25Weight</a> returns "Xapian::BM25Weight" here).<p>
If you don't want to support the remote backend, you can use the default implementation which simply returns an empty string.
<p>Reimplemented from <a class="el" href="classXapian_1_1Weight.html#afd3b445fb1955aae3d7c32aae3ba7b4">Xapian::Weight</a>.</p>
</div>
</div><p>
<a class="anchor" name="3cb90ec9c8ef2866dfa405d3490d4cc3"></a><!-- doxytag: member="Xapian::TradWeight::serialise" ref="3cb90ec9c8ef2866dfa405d3490d4cc3" args="() const " -->
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<td class="memname">std::string Xapian::TradWeight::serialise </td>
<td>(</td>
<td class="paramname"> </td>
<td> ) </td>
<td> const<code> [virtual]</code></td>
</tr>
</table>
</div>
<div class="memdoc">
<p>
Return this object's parameters serialised as a single string.
<p>
If you don't want to support the remote backend, you can use the default implementation which simply throws <a class="el" href="classXapian_1_1UnimplementedError.html" title="UnimplementedError indicates an attempt to use an unimplemented feature.">Xapian::UnimplementedError</a>.
<p>Reimplemented from <a class="el" href="classXapian_1_1Weight.html#cf568da52a87e6a6786400dbd0a79edf">Xapian::Weight</a>.</p>
</div>
</div><p>
<a class="anchor" name="ce5aae016fc57407c7f7f5f0f3d7b5c0"></a><!-- doxytag: member="Xapian::TradWeight::unserialise" ref="ce5aae016fc57407c7f7f5f0f3d7b5c0" args="(const std::string &s) const " -->
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<td class="memname"><a class="el" href="classXapian_1_1TradWeight.html">TradWeight</a>* Xapian::TradWeight::unserialise </td>
<td>(</td>
<td class="paramtype">const std::string & </td>
<td class="paramname"> <em>s</em> </td>
<td> ) </td>
<td> const<code> [virtual]</code></td>
</tr>
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<p>
Unserialise parameters.
<p>
This method unserialises parameters serialised by the <em><a class="el" href="classXapian_1_1TradWeight.html#3cb90ec9c8ef2866dfa405d3490d4cc3" title="Return this object's parameters serialised as a single string.">serialise()</a></em> method and allocates and returns a new object initialised with them.<p>
If you don't want to support the remote backend, you can use the default implementation which simply throws <a class="el" href="classXapian_1_1UnimplementedError.html" title="UnimplementedError indicates an attempt to use an unimplemented feature.">Xapian::UnimplementedError</a>.<p>
Note that the returned object will be deallocated by <a class="el" href="namespaceXapian.html" title="The Xapian namespace contains public interfaces for the Xapian library.">Xapian</a> after use with "delete". If you want to handle the deletion in a special way (for example when wrapping the <a class="el" href="namespaceXapian.html" title="The Xapian namespace contains public interfaces for the Xapian library.">Xapian</a> API for use from another language) then you can define a static <code>operator delete</code> method in your subclass as shown here: <a href="http://trac.xapian.org/ticket/554#comment:1">http://trac.xapian.org/ticket/554#comment:1</a><p>
<dl compact><dt><b>Parameters:</b></dt><dd>
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<tr><td valign="top"></td><td valign="top"><em>s</em> </td><td>A string containing the serialised parameters. </td></tr>
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<p>Reimplemented from <a class="el" href="classXapian_1_1Weight.html#031c3e0db3ae50e801b324e71a44c140">Xapian::Weight</a>.</p>
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<hr>The documentation for this class was generated from the following file:<ul>
<li>xapian/<a class="el" href="weight_8h.html">weight.h</a></ul>
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<address><small>
Documentation for Xapian (version 1.2.12).<br>
Generated on 27 Jun 2012 by
<a href="http://www.doxygen.org/">Doxygen 1.5.9</a>.
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