<chapter id="administration">
- <!-- $Id: administration.xml,v 1.28 2006-04-24 12:53:02 marc Exp $ -->
+ <!-- $Id: administration.xml,v 1.34 2006-06-12 09:39:18 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
<sect1 id="administration-ranking">
- <title>Static and Dynamic Ranking</title>
+ <title>Relevance Ranking and Sorting of Result Sets</title>
+
+ <sect2>
+ <title>Overview</title>
+ <para>
+ The default ordering of a result set is left up to the server,
+ which inside Zebra means sorting in ascending document ID order.
+ This is not always the order humans want to browse the sometimes
+ quite large hit sets. Ranking and sorting comes to the rescue.
+ </para>
+
+ <para>
+ In cases where a good presentation ordering can be computed at
+ indexing time, we can use a fixed <literal>static ranking</literal>
+ scheme, which is provided for the <literal>alvis</literal>
+ indexing filter. This defines a fixed ordering of hit lists,
+ independently of the query issued.
+ </para>
+
+ <para>
+ There are cases, however, where relevance of hit set documents is
+ highly dependent on the query processed.
+ Simply put, <literal>dynamic relevance ranking</literal>
+ sorts a set of retrieved
+ records such
+ that those most likely to be relevant to your request are
+ retrieved first.
+ Internally, Zebra retrieves all documents that satisfy your
+ query, and re-orders the hit list to arrange them based on
+ a measurement of similarity between your query and the content of
+ each record.
+ </para>
+
+ <para>
+ Finally, there are situations where hit sets of documents should be
+ <literal>sorted</literal> during query time according to the
+ lexicographical ordering of certain sort indexes created at
+ indexing time.
+ </para>
+ </sect2>
+
+
+ <sect2 id="administration-ranking-static">
+ <title>Static Ranking</title>
<para>
Zebra uses internally inverted indexes to look up term occurencies
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.
+ Zero
+ is the ``best'' rank, as it occurs at the
+ beginning of the list; higher numbers represent worse scores.
</para>
<para>
The experimental <literal>alvis</literal> filter provides a
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.
+ See <xref linkend="record-model-alvisxslt"/> for the gory details.
</para>
+ </sect2>
+
+
+ <sect2 id="administration-ranking-dynamic">
+ <title>Dynamic Ranking</title>
<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
+ In order to fiddle with the static rank order, it is necessary to
+ invoke additional re-ranking/re-ordering using dynamic
+ ranking or score functions. These functions return positive
+ integer scores, where <emphasis>highest</emphasis> score is
+ ``best'';
+ hit sets are 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).
+ ascending 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!):
+ Dynamic ranking is enabled by a directive like one of the
+ following in the zebra config file (use only one of these a time!):
<screen>
- rank: rank-1 # default
- rank: rank-static # dummy
- rank: zvrank # TDF-IDF like
+ rank: rank-1 # default TDF-IDF like
+ rank: rank-static # dummy do-nothing
</screen>
- Notice that the <literal>rank-1</literal> and
- <literal>zvrank</literal> do not use the static rank
+ Notice that the <literal>rank-1</literal> algorithm
+ does not use the static rank
information in the list keys, and will produce the same ordering
- with our without static ranking enabled.
+ with or 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
+ in order to preserve the static ordering of hit sets that would
+ have been produced had it not been invoked.
+ Obviously, to combine static and dynamic ranking usefully,
+ it is necessary
to make a new ranking
- function, which is left
+ function; this is left
as an exercise for the reader.
</para>
-
+
+
+ <para>
+ Dynamic ranking is done at query time rather than
+ indexing time (this is why we
+ call it ``dynamic ranking'' in the first place ...)
+ It is invoked by adding
+ the Bib-1 relation attribute with
+ value ``relevance'' to the PQF query (that is,
+ <literal>@attr 2=102</literal>, see also
+ <ulink url="ftp://ftp.loc.gov/pub/z3950/defs/bib1.txt">
+ The BIB-1 Attribute Set Semantics</ulink>).
+ To find all articles with the word <literal>Eoraptor</literal> in
+ the title, and present them relevance ranked, issue the PQF query:
+ <screen>
+ @attr 2=102 @attr 1=4 Eoraptor
+ </screen>
+ </para>
+
+ <para>
+ The default <literal>rank-1</literal> ranking module implements a
+ TF-IDF (Term Frequecy over Inverse Document Frequency) like algorithm.
+ </para>
+
+ <warning>
+ <para>
+ Notice that <literal>dynamic ranking</literal> is not compatible
+ with <literal>estimated hit sizes</literal>, as all documents in
+ a hit set must be acessed to compute the correct placing in a
+ ranking sorted list. Therefore the use attribute setting
+ <literal>@attr 2=102</literal> clashes with
+ <literal>@attr 9=integer</literal>.
+ </para>
+ </warning>
+
+ <para>
+ It is possible to apply dynamic ranking on only parts of the PQF query:
+ <screen>
+ @and @attr 2=102 @attr 1=1010 Utah @attr 1=1018 Springer
+ </screen>
+ searches for all documents which have the term 'Utah' on the
+ body of text, and which have the term 'Springer' in the publisher
+ field, and sort them in the order of the relvance ranking made on
+ the body-of-text index only.
+ </para>
+ <para>
+ Ranking weights may be used to pass a value to a ranking
+ algorithm, using the non-standard BIB-1 attribute type 9.
+ This allows one branch of a query to use one value while
+ another branch uses a different one. For example, we can search
+ for <literal>utah</literal> in the title index with weight 30, as
+ well as in the ``any'' index with weight 20:
+ <screen>
+ @attr 2=102 @or @attr 9=30 @attr 1=4 utah @attr 9=20 utah
+ </screen>
+ </para>
+ <warning>
+ <para>
+ The ranking-weight feature is experimental. It may change in future
+ releases of zebra, and is not production mature.
+ </para>
+ </warning>
+
+ <para>
+ Notice that dynamic ranking can be enabled in sever side CQL
+ query expansion by adding <literal>@attr 2=102</literal> to
+ the CQL config file. For example
+ <screen>
+ relationModifier.relevant = 2=102
+ </screen>
+ invokes dynamic ranking each time a CQL query of the form
+ <screen>
+ Z> querytype cql
+ Z> f alvis.text =/relevant house
+ </screen>
+ is issued. Dynamic ranking can also be automatically used on
+ specific CQL indexes by (for example) setting
+ <screen>
+ index.alvis.text = 1=text 2=102
+ </screen>
+ which then invokes dynamic ranking each time a CQL query of the form
+ <screen>
+ Z> querytype cql
+ Z> f alvis.text = house
+ </screen>
+ is issued.
+ </para>
+
+ </sect2>
+
+
+ <sect2 id="administration-ranking-sorting">
+ <title>Sorting</title>
+ <para>
+ Zebra sorts efficiently using special sorting indexes
+ (type=<literal>s</literal>; so each sortable index must be known
+ at indexing time, specified in the configuration of record
+ indexing. For example, to enable sorting according to the BIB-1
+ <literal>Date/time-added-to-db</literal> field, one could add the line
+ <screen>
+ xelm /*/@created Date/time-added-to-db:s
+ </screen>
+ to any <literal>.abs</literal> record-indexing configuration file.
+ Similarily, one could add an indexing element of the form
+ <screen><![CDATA[
+ <z:index name="date-modified" type="s">
+ <xsl:value-of select="some/xpath"/>
+ </z:index>
+ ]]></screen>
+ to any <literal>alvis</literal>-filter indexing stylesheet.
+ </para>
+ <para>
+ Indexing can be specified at searching time using a query term
+ carrying the non-standard
+ BIB-1 attribute-type <literal>7</literal>. This removes the
+ need to send a Z39.50 <literal>Sort Request</literal>
+ separately, and can dramatically improve latency when the client
+ and server are on separate networks.
+ The sorting part of the query is separate from the rest of the
+ query - the actual search specification - and must be combined
+ with it using OR.
+ </para>
+ <para>
+ A sorting subquery needs two attributes: an index (such as a
+ BIB-1 type-1 attribute) specifying which index to sort on, and a
+ type-7 attribute whose value is be <literal>1</literal> for
+ ascending sorting, or <literal>2</literal> for descending. The
+ term associated with the sorting attribute is the priority of
+ the sort key, where <literal>0</literal> specifies the primary
+ sort key, <literal>1</literal> the secondary sort key, and so
+ on.
+ </para>
+ <para>For example, a search for water, sort by title (ascending),
+ is expressed by the PQF query
+ <screen>
+ @or @attr 1=1016 water @attr 7=1 @attr 1=4 0
+ </screen>
+ whereas a search for water, sort by title ascending,
+ then date descending would be
+ <screen>
+ @or @or @attr 1=1016 water @attr 7=1 @attr 1=4 0 @attr 7=2 @attr 1=30 1
+ </screen>
+ </para>
+ <para>
+ Notice the fundamental differences between <literal>dynamic
+ ranking</literal> and <literal>sorting</literal>: there can be
+ only one ranking function defined and configured; but multiple
+ sorting indexes can be specified dynamically at search
+ time. Ranking does not need to use specific indexes, so
+ dynamic ranking can be enabled and disabled without
+ re-indexing; whereas, sorting indexes need to be
+ defined before indexing.
+ </para>
+
+ </sect2>
+
+
</sect1>
<sect1 id="administration-extended-services">
</chapter>
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projects / idzebra-moved-to-github.git / blobdiff