+
+
+ <sect1 id="administration-ranking">
+ <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
+ 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 configuration file, the internal document
+ keys used for ordering are augmented by a preceding 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>.
+ 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
+ directive to fetch static rank information out of the indexed XML
+ records, thus making <emphasis>all</emphasis> hit sets ordered
+ 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 gory details.
+ </para>
+ </sect2>
+
+
+ <sect2 id="administration-ranking-dynamic">
+ <title>Dynamic Ranking</title>
+ <para>
+ 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>descending</emphasis>
+ scores (in contrary
+ to the index lists which are sorted according to
+ ascending rank number and document ID).
+ </para>
+ <para>
+ Dynamic ranking is enabled by a directive like one of the
+ following in the zebra configuration file (use only one of these a time!):
+ <screen>
+ rank: rank-1 # default TDF-IDF like
+ rank: rank-static # dummy do-nothing
+ </screen>
+ </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="&url.z39.50;bib1.html">
+ The BIB-1 Attribute Set Semantics</ulink>, also in
+ <ulink url="&url.z39.50.attset.bib1;">HTML</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>
+
+ <sect3 id="administration-ranking-dynamic-rank1">
+ <title>Dynamically ranking using PQF queries with the 'rank-1'
+ algorithm</title>
+
+ <para>
+ The default <literal>rank-1</literal> ranking module implements a
+ TF/IDF (Term Frequecy over Inverse Document Frequency) like
+ algorithm. In contrast to the usual defintion of TF/IDF
+ algorithms, which only considers searching in one full-text
+ index, this one works on multiple indexes at the same time.
+ More precisely,
+ Zebra does boolean queries and searches in specific addressed
+ indexes (there are inverted indexes pointing from terms in the
+ dictionary to documents and term positions inside documents).
+ It works like this:
+ <variablelist>
+ <varlistentry>
+ <term>Query Components</term>
+ <listitem>
+ <para>
+ First, the boolean query is dismantled into it's principal components,
+ i.e. atomic queries where one term is looked up in one index.
+ For example, the query
+ <screen>
+ @attr 2=102 @and @attr 1=1010 Utah @attr 1=1018 Springer
+ </screen>
+ is a boolean AND between the atomic parts
+ <screen>
+ @attr 2=102 @attr 1=1010 Utah
+ </screen>
+ and
+ <screen>
+ @attr 2=102 @attr 1=1018 Springer
+ </screen>
+ which gets processed each for itself.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>Atomic hit lists</term>
+ <listitem>
+ <para>
+ Second, for each atomic query, the hit list of documents is
+ computed.
+ </para>
+ <para>
+ In this example, two hit lists for each index
+ <literal>@attr 1=1010</literal> and
+ <literal>@attr 1=1018</literal> are computed.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>Atomic scores</term>
+ <listitem>
+ <para>
+ Third, each document in the hit list is assigned a score (_if_ ranking
+ is enabled and requested in the query) using a TF/IDF scheme.
+ </para>
+ <para>
+ In this example, both atomic parts of the query assign the magic
+ <literal>@attr 2=102</literal> relevance attribute, and are
+ to be used in the relevance ranking functions.
+ </para>
+ <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 relevance ranking made on
+ the body-of-text index only.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>Hit list merging</term>
+ <listitem>
+ <para>
+ Fourth, the atomic hit lists are merged according to the boolean
+ conditions to a final hit list of documents to be returned.
+ </para>
+ <para>
+ This step is always performed, independently of the fact that
+ dynamic ranking is enabled or not.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>Document score computation</term>
+ <listitem>
+ <para>
+ Fifth, the total score of a document is computed as a linear
+ combination of the atomic scores of the atomic hit lists
+ </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
+ <literal>@attr 1=4</literal> index with weight 30, as
+ well as in the <literal>@attr 1=1010</literal> index with weight 20:
+ <screen>
+ @attr 2=102 @or @attr 9=30 @attr 1=4 utah @attr 9=20 @attr 1=1010 city
+ </screen>
+ </para>
+ <para>
+ The default weight is
+ sqrt(1000) ~ 34 , as the Z39.50 standard prescribes that the top score
+ is 1000 and the bottom score is 0, encoded in integers.
+ </para>
+ <warning>
+ <para>
+ The ranking-weight feature is experimental. It may change in future
+ releases of zebra.
+ </para>
+ </warning>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>Re-sorting of hit list</term>
+ <listitem>
+ <para>
+ Finally, the final hit list is re-ordered according to scores.
+ </para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+
+
+<!--
+Still need to describe the exact TF/IDF formula. Here's the info, need -->
+<!--to extract it in human readable form .. MC
+
+static int calc (void *set_handle, zint sysno, zint staticrank,
+ int *stop_flag)
+{
+ int i, lo, divisor, score = 0;
+ struct rank_set_info *si = (struct rank_set_info *) set_handle;
+
+ if (!si->no_rank_entries)
+ return -1; /* ranking not enabled for any terms */
+
+ for (i = 0; i < si->no_entries; i++)
+ {
+ yaz_log(log_level, "calc: i=%d rank_flag=%d lo=%d",
+ i, si->entries[i].rank_flag, si->entries[i].local_occur);
+ if (si->entries[i].rank_flag && (lo = si->entries[i].local_occur))
+ score += (8+log2_int (lo)) * si->entries[i].global_inv *
+ si->entries[i].rank_weight;
+ }
+ divisor = si->no_rank_entries * (8+log2_int (si->last_pos/si->no_entries));
+ score = score / divisor;
+ yaz_log(log_level, "calc sysno=" ZINT_FORMAT " score=%d", sysno, score);
+ if (score > 1000)
+ score = 1000;
+ /* reset the counts for the next term */
+ for (i = 0; i < si->no_entries; i++)
+ si->entries[i].local_occur = 0;
+ return score;
+}
+
+
+where lo = si->entries[i].local_occur is the local documents term-within-index frequency, si->entries[i].global_inv represents the IDF part (computed in static void *begin()), and
+si->entries[i].rank_weight is the weight assigner per index (default 34, or set in the @attr 9=xyz magic)
+
+Finally, the IDF part is computed as:
+
+static void *begin (struct zebra_register *reg,
+ void *class_handle, RSET rset, NMEM nmem,
+ TERMID *terms, int numterms)
+{
+ struct rank_set_info *si =
+ (struct rank_set_info *) nmem_malloc (nmem,sizeof(*si));
+ int i;
+
+ yaz_log(log_level, "rank-1 begin");
+ si->no_entries = numterms;
+ si->no_rank_entries = 0;
+ si->nmem=nmem;
+ si->entries = (struct rank_term_info *)
+ nmem_malloc (si->nmem, sizeof(*si->entries)*numterms);
+ for (i = 0; i < numterms; i++)
+ {
+ zint g = rset_count(terms[i]->rset);
+ yaz_log(log_level, "i=%d flags=%s '%s'", i,
+ terms[i]->flags, terms[i]->name );
+ if (!strncmp (terms[i]->flags, "rank,", 5))
+ {
+ const char *cp = strstr(terms[i]->flags+4, ",w=");
+ si->entries[i].rank_flag = 1;
+ if (cp)
+ si->entries[i].rank_weight = atoi (cp+3);
+ else
+ si->entries[i].rank_weight = 34; /* sqrroot of 1000 */
+ yaz_log(log_level, " i=%d weight=%d g="ZINT_FORMAT, i,
+ si->entries[i].rank_weight, g);
+ (si->no_rank_entries)++;
+ }
+ else
+ si->entries[i].rank_flag = 0;
+ si->entries[i].local_occur = 0; /* FIXME */
+ si->entries[i].global_occur = g;
+ si->entries[i].global_inv = 32 - log2_int (g);
+ yaz_log(log_level, " global_inv = %d g = " ZINT_FORMAT,
+ (int) (32-log2_int (g)), g);
+ si->entries[i].term = terms[i];
+ si->entries[i].term_index=i;
+ terms[i]->rankpriv = &(si->entries[i]);
+ }
+ return si;
+}
+
+
+where g = rset_count(terms[i]->rset) is the count of all documents in this specific index hit list, and the IDF part then is
+
+ si->entries[i].global_inv = 32 - log2_int (g);
+ -->
+
+ </para>
+
+
+ <para>
+ The <literal>rank-1</literal> algorithm
+ does not use the static rank
+ information in the list keys, and will produce the same ordering
+ with or without static ranking enabled.
+ </para>
+
+ </sect3>
+
+ <!--
+ <sect3 id="administration-ranking-dynamic-rank1">
+ <title>Dynamically ranking PQF queries with the 'rank-static'
+ algorithm</title>
+ <para>
+ The dummy <literal>rank-static</literal> reranking/scoring
+ function returns just
+ <literal>score = max int - staticrank</literal>
+ 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; this is left
+ as an exercise for the reader.
+ </para>
+ </sect3>
+ -->
+
+
+ <warning>
+ <para>
+ <literal>Dynamic ranking</literal> is not compatible
+ with <literal>estimated hit sizes</literal>, as all documents in
+ a hit set must be accessed 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>
+
+ <!--
+ we might want to add ranking like this:
+ UNPUBLISHED:
+ Simple BM25 Extension to Multiple Weighted Fields
+ Stephen Robertson, Hugo Zaragoza and Michael Taylor
+ Microsoft Research
+ ser@microsoft.com
+ hugoz@microsoft.com
+ mitaylor2microsoft.com
+ -->
+
+
+ <sect3 id="administration-ranking-dynamic-cql">
+ <title>Dynamically ranking CQL queries</title>
+ <para>
+ Dynamic ranking can be enabled during sever side CQL
+ query expansion by adding <literal>@attr 2=102</literal>
+ chunks 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>
+
+ </sect3>
+
+ </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.
+ Similarly, 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">
+ <title>Extended Services: Remote Insert, Update and Delete</title>
+
+ <para>
+ The extended services are not enabled by default in zebra - due to the
+ fact that they modify the system.
+ In order to allow anybody to update, use
+ <screen>
+ perm.anonymous: rw
+ </screen>
+ in the main zebra configuration file <filename>zebra.cfg</filename>.
+ Or, even better, allow only updates for a particular admin user. For
+ user <literal>admin</literal>, you could use:
+ <screen>
+ perm.admin: rw
+ passwd: passwordfile
+ </screen>
+ And in <filename>passwordfile</filename>, specify users and
+ passwords as colon seperated strings:
+ <screen>
+ admin:secret
+ </screen>
+ </para>
+ <para>
+ We can now start a yaz-client admin session and create a database:
+ <screen>
+ <![CDATA[
+ $ yaz-client localhost:9999 -u admin/secret
+ Z> adm-create
+ ]]>
+ </screen>
+ Now the <literal>Default</literal> database was created,
+ we can insert an XML file (esdd0006.grs
+ from example/gils/records) and index it:
+ <screen>
+ <![CDATA[
+ Z> update insert 1 esdd0006.grs
+ ]]>
+ </screen>
+ The 3rd parameter - <literal>1</literal> here -
+ is the opaque record ID from <literal>Ext update</literal>.
+ It a record ID that <emphasis>we</emphasis> assign to the record
+ in question. If we do not
+ assign one, the usual rules for match apply (recordId: from zebra.cfg).
+ </para>
+ <para>
+ Actually, we should have a way to specify "no opaque record id" for
+ yaz-client's update command.. We'll fix that.
+ </para>
+ <para>
+ The newly inserted record can be searched as usual:
+ <screen>
+ <![CDATA[
+ Z> f utah
+ Sent searchRequest.
+ Received SearchResponse.
+ Search was a success.
+ Number of hits: 1, setno 1
+ SearchResult-1: term=utah cnt=1
+ records returned: 0
+ Elapsed: 0.014179
+ ]]>
+ </screen>
+ </para>
+ <para>
+ Let's delete the beast:
+ <screen>
+ <![CDATA[
+ Z> update delete 1
+ No last record (update ignored)
+ Z> update delete 1 esdd0006.grs
+ Got extended services response
+ Status: done
+ Elapsed: 0.072441
+ Z> f utah
+ Sent searchRequest.
+ Received SearchResponse.
+ Search was a success.
+ Number of hits: 0, setno 2
+ SearchResult-1: term=utah cnt=0
+ records returned: 0
+ Elapsed: 0.013610
+ ]]>
+ </screen>
+ </para>
+ <para>
+ If shadow register is enabled in your
+ <filename>zebra.cfg</filename>,
+ you must run the adm-commit command
+ <screen>
+ <![CDATA[
+ Z> adm-commit
+ ]]>
+ </screen>
+ after each update session in order write your changes from the
+ shadow to the life register space.
+ </para>
+ <para>
+ Extended services are also available from the YAZ client layer. An
+ example of an YAZ-PHP extended service transaction is given here:
+ <screen>
+ <![CDATA[
+ $record = '<record><title>A fine specimen of a record</title></record>';
+
+ $options = array('action' => 'recordInsert',
+ 'syntax' => 'xml',
+ 'record' => $record,
+ 'databaseName' => 'mydatabase'
+ );
+
+ yaz_es($yaz, 'update', $options);
+ yaz_es($yaz, 'commit', array());
+ yaz_wait();
+
+ if ($error = yaz_error($yaz))
+ echo "$error";
+ ]]>
+ </screen>
+ The <literal>action</literal> parameter can be any of
+ <literal>recordInsert</literal> (will fail if the record already exists),
+ <literal>recordReplace</literal> (will fail if the record does not exist),
+ <literal>recordDelete</literal> (will fail if the record does not
+ exist), and
+ <literal>specialUpdate</literal> (will insert or update the record
+ as needed).
+ </para>
+ <para>
+ If a record is inserted
+ using the action <literal>recordInsert</literal>
+ one can specify the optional
+ <literal>recordIdOpaque</literal> parameter, which is a
+ client-supplied, opaque record identifier. This identifier will
+ replace zebra's own automagic identifier generation.
+ </para>
+ <para>
+ When using the action <literal>recordReplace</literal> or
+ <literal>recordDelete</literal>, one must specify the additional
+ <literal>recordIdNumber</literal> parameter, which must be an
+ existing Zebra internal system ID number. When retrieving existing
+ records, the ID number is returned in the field
+ <literal>/*/id:idzebra/localnumber</literal> in the namespace
+ <literal>xmlns:id="http://www.indexdata.dk/zebra/"</literal>,
+ where it can be picked up for later record updates or deletes.
+ </para>
+ </sect1>
+
+
+ <sect1 id="gfs-config">
+ <title>YAZ Frontend Virtual Hosts</title>
+ <para>
+ <command>zebrasrv</command> uses the YAZ server frontend and does
+ support multiple virtual servers behind multiple listening sockets.
+ </para>
+ &zebrasrv-virtual;
+
+ <para>
+ Section "Virtual Hosts" in the YAZ manual.
+ <filename>http://www.indexdata.dk/yaz/doc/server.vhosts.tkl</filename>
+ </para>
+ </sect1>
+
+
projects / idzebra-moved-to-github.git / blobdiff