<chapter id="administration">
- <!-- $Id: administration.xml,v 1.22 2006-02-15 11:07:47 marc Exp $ -->
+ <!-- $Id: administration.xml,v 1.23 2006-02-15 12:08:47 marc Exp $ -->
<title>Administrating Zebra</title>
<!-- ### It's a bit daft that this chapter (which describes half of
the configuration-file formats) is separated from
<screen>
register: /d1:500M
-
shadow: /scratch1:100M /scratch2:200M
</screen>
</sect2>
</sect1>
+
+
+ <sect1 id="administration-ranking">
+ <title>Static and Dynamic Ranking</title>
+
+ <para>
+ Zebra uses internally inverted indexes to look up term occurencies
+ in documents. Multiple queries from different indexes can be
+ combined by the binary boolean operations <literal>AND</literal>,
+ <literal>OR</literal> and/or <literal>NOT</literal> (which
+ is in fact a binary <literal>AND NOT</literal> operation).
+ To ensure fast query execution
+ speed, all indexes have to be sorted in the same order.
+ </para>
+ <para>
+ The indexes are normally sorted according to document
+ <literal>ID</literal> in
+ ascending order, and any query which does not invoke a special
+ re-ranking function will therefore retrieve the result set in
+ document
+ <literal>ID</literal>
+ order.
+ </para>
+ <para>
+ If one defines the
+ <screen>
+ staticrank: 1
+ </screen>
+ directive in the main core Zebra config file, the internal document
+ keys used for ordering are augmented by a preceeding integer, which
+ contains the static rank of a given document, and the index lists
+ are ordered
+ first by ascending static rank,
+ then by ascending document <literal>ID</literal>.
+ </para>
+ <para>
+ This implies that the default rank <literal>0</literal>
+ is the best rank at the
+ beginning of the list, and <literal>max int</literal>
+ is the worst static rank.
+ </para>
+ <para>
+ The experimental <literal>alvis</literal> filter provides a
+ directive to fetch static rank information out of the indexed XML
+ records, thus making <emphasis>all</emphasis> hit sets orderd
+ after <emphasis>ascending</emphasis> static
+ rank, and for those doc's which have the same static rank, ordered
+ after <emphasis>ascending</emphasis> doc <literal>ID</literal>.
+ See <xref linkend="record-model-alvisxslt"/> for the glory details.
+ </para>
+ <para>
+ If one wants to do a little fiddeling with the static rank order,
+ one has to invoke additional re-ranking/re-ordering using dynamic
+ reranking or score functions. These functions return positive
+ interger scores, where <emphasis>highest</emphasis> score is
+ <emphasis>best</emphasis>, which means that the
+ hit sets will be sorted according to
+ <emphasis>decending</emphasis>
+ scores (in contrary
+ to the index lists which are sorted according to
+ <emphasis>ascending</emphasis> rank number and document ID).
+ </para>
+ <!--
+ <para>
+ Those are defined in the zebra C source files
+ <screen>
+ "rank-1" : zebra/index/rank1.c
+ default TF/IDF like zebra dynamic ranking
+ "rank-static" : zebra/index/rankstatic.c
+ do-nothing dummy static ranking (this is just to prove
+ that the static rank can be used in dynamic ranking functions)
+ "zvrank" : zebra/index/zvrank.c
+ many different dynamic TF/IDF ranking functions
+ </screen>
+ </para>
+ -->
+ <para>
+ Those are in the zebra config file enabled by a directive like (use
+ only one of these a time!):
+ <screen>
+ rank: rank-1 # default
+ rank: rank-static # dummy
+ rank: zvrank # TDF-IDF like
+ </screen>
+ Notice that the <literal>rank-1</literal> and
+ <literal>zvrank</literal> do not use the static rank
+ information in the list keys, and will produce the same ordering
+ with our without static ranking enabled.
+ </para>
+ <para>
+ The dummy <literal>rank-static</literal> reranking/scoring
+ function returns just
+ <literal>score = max int - staticrank</literal>
+ in order to preserve the ordering of hit sets with and without it's
+ call.
+ Obviously, to combine static and dynamic ranking usefully, one wants
+ to make a new ranking
+ function, which is left
+ as an exercise for the reader.
+ </para>
+
+ </sect1>
+
</chapter>
+
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