typo

[idzebra-moved-to-github.git] / doc / querymodel.xml

 <chapter id="querymodel">
  <!-- $Id: querymodel.xml,v 1.20 2006-06-30 14:48:04 heikki Exp $ -->
  <title>Query Model</title>
  
  <sect1 id="querymodel-overview">
   <title>Query Model Overview</title>  
   
   <sect2 id="querymodel-query-languages">
    <title>Query Languages</title>
 
    <para>
     Zebra is born as a networking Information Retrieval engine adhering
     to the international standards 
     <ulink url="&url.z39.50;">Z39.50</ulink> and
     <ulink url="&url.sru;">SRU</ulink>,
     and implement the 
     <literal>type-1 Reverse Polish Notation (RPN)</literal> query
     model defined there.
     Unfortunately, this model has only defined a binary
     encoded representation, which is used as transport packaging in
     the Z39.50 protocol layer. This representation is not human
     readable, nor defines any convenient way to specify queries. 
    </para>
    <para>
     Since the <literal>type-1 (RPN)</literal> 
     query structure has no direct, useful string
     representation, every client application needs to provide some
     form of mapping from a local query notation or representation to it.
    </para>
    
    
    <sect3 id="querymodel-query-languages-pqf">
     <title>Prefix Query Format (PQF)</title>
     <para>
      Index Data has defined a textual representation in the 
      <ulink url="&url.yaz.pqf;">Prefix Query Format</ulink>, short
      <emphasis>PQF</emphasis>, which maps 
      one-to-one to binary encoded  
      <emphasis>type-1 RPN</emphasis> queries.
      PQF has been adopted by other
      parties developing Z39.50 software, and is often referred to as
      <literal>Prefix Query Notation</literal>, or in short 
      <literal>PQN</literal>. See       
      <xref linkend="querymodel-pqf"/> for further explanations and
      descriptions of Zebra's capabilities.  
     </para>
    </sect3>    
    
    <sect3 id="querymodel-query-languages-cql">
     <title>Common Query Language (CQL)</title>
     <para>
      The query model of the type-1 RPN,
      expressed in PQF/PQN is natively supported. 
      On the other hand, the default SRU
      web services <emphasis>Common Query Language</emphasis>
      <ulink url="&url.cql;">CQL</ulink> is not natively supported.
     </para>
     <para>
      Zebra can be configured to understand and map CQL to PQF. See
      <xref linkend="querymodel-cql-to-pqf"/>.
     </para>
    </sect3>    
 
   </sect2>

   <sect2 id="querymodel-operation-types">
    <title>Operation types</title>
    <para>
     Zebra supports all of the three different
     <literal>Z39.50/SRU</literal> operations defined in the
     standards: <literal>explain</literal>, <literal>search</literal>, 
     and <literal>scan</literal>. A short description of the
     functionality and purpose of each is quite in order here. 
    </para>

    <sect3 id="querymodel-operation-type-explain">
     <title>Explain Operation</title>
     <para>
      The <emphasis>syntax</emphasis> of Z39.50/SRU queries is
      well known to any client, but the specific
      <emphasis>semantics</emphasis> - taking into account a
      particular servers functionalities and abilities - must be
      discovered from case to case. Enters the 
      <literal>explain</literal> operation, which provides the means
      for learning which  
      <emphasis>fields</emphasis> (also called
      <emphasis>indexes</emphasis> or <emphasis>access points</emphasis>)
      are provided, which default parameter the server uses, which
      retrieve document formats are defined, and which specific parts
      of the general query model are supported.      
     </para>
     <para>
      The Z39.50 embeds the <literal>explain</literal> operation
      by performing a 
      <literal>search</literal> in the magic 
      <literal>IR-Explain-1</literal> database;
      see <xref linkend="querymodel-exp1"/>. 
     </para>
     <para>
      In SRU, <literal>explain</literal> is an entirely  separate
      operation, which returns an  <literal>ZeeRex
      XML</literal> record according to the 
      structure defined by the protocol.
     </para>
     <para>
      In both cases, the information gathered through
      <literal>explain</literal> operations can be used to
      auto-configure a client user interface to the servers
      capabilities.  
     </para>
    </sect3>

    <sect3 id="querymodel-operation-type-search">
     <title>Search Operation</title>
     <para>
      Search and retrieve interactions are the raison d'être. 
      They are used to query the remote database and
      return search result documents.  Search queries span from
      simple free text searches to nested complex boolean queries,
      targeting specific indexes, and possibly enhanced with many
      query semantic specifications. Search interactions are the heart
      and soul of Z39.50/SRU servers.
     </para>
    </sect3>

    <sect3 id="querymodel-operation-type-scan">
     <title>Scan Operation</title>
     <para>
      The <literal>scan</literal> operation is a helper functionality,
       which operates on one index or access point a time. 
     </para>
     <para>
      It provides
      the means to investigate the content of specific indexes.
      Scanning an index returns a handful of terms actually found in
      the indexes, and in addition the <literal>scan</literal>
      operation returns the number of documents indexed by each term.
      A search client can use this information to propose proper
      spelling of search terms, to auto-fill search boxes, or to 
      display  controlled vocabularies.
     </para>
    </sect3>

   </sect2>

 </sect1>

  
  <sect1 id="querymodel-pqf">
   <title>Prefix Query Format syntax and semantics</title>
   <para>
    The <ulink url="&url.yaz.pqf;">PQF grammar</ulink>
    is documented in the YAZ manual, and shall not be
    repeated here. This textual PQF representation
    is not transmistted to Zebra during search, but it is in the
    client mapped to the equivalent Z39.50 binary 
    query parse tree. 
   </para>
   
   <sect2 id="querymodel-pqf-tree">
    <title>PQF tree structure</title>
    <para>
     The PQF parse tree - or the equivalent textual representation -
     may start with one specification of the 
     <emphasis>attribute set</emphasis> used. Following is a query
     tree, which 
     consists of <emphasis>atomic query parts (APT)</emphasis> or
     <emphasis>named result sets</emphasis>, eventually
     paired by <emphasis>boolean binary operators</emphasis>, and 
     finally  <emphasis>recursively combined </emphasis> into 
     complex query trees.   
    </para>
    
    <sect3 id="querymodel-attribute-sets">
     <title>Attribute sets</title>
     <para>
      Attribute sets define the exact meaning and semantics of queries
      issued. Zebra comes with some predefined attribute set
      definitions, others can easily be defined and added to the
      configuration.
     </para>

     
     <table id="querymodel-attribute-sets-table"
      frame="all" rowsep="1" colsep="1" align="center">

      <caption>Attribute sets predefined in Zebra</caption>
       
       <thead>
       <tr>
         <td>Attribute set</td>
         <td>Short hand</td>
         <td>Status</td>
         <td>Notes</td>
        </tr>
      </thead>
      
       <tbody>
        <tr>
         <td><literal>Explain</literal></td>
         <td><literal>exp-1</literal></td>
         <td>Special attribute set used on the special automagic
          <literal>IR-Explain-1</literal> database to gain information on
          server capabilities, database names, and database
          and semantics.</td>
         <td>predefined</td>
        </tr>
        <tr>
         <td><literal>Bib1</literal></td>
         <td><literal>bib-1</literal></td>
         <td>Standard PQF query language attribute set which defines the
          semantics of Z39.50 searching. In addition, all of the
          non-use attributes (type 2-9) define the hard-wired 
          Zebra internal query
          processing.</td>
         <td>default</td>
        </tr>
        <tr>
         <td><literal>GILS</literal></td>
         <td><literal>gils</literal></td>
         <td>Extension to the <literal>Bib1</literal> attribute set.</td>
         <td>predefined</td>
        </tr>
        <!--
        <tr>
         <td><literal>IDXPATH</literal></td>
         <td><literal>idxpath</literal></td>
         <td>Hardwired XPATH like attribute set, only available for
             indexing with the GRS record model</td>
         <td>depreciated</td>
        </tr>
        -->
       </tbody>
     </table>
    </sect3>

    <para>
     The <literal>use attributes (type 1)</literal> mappings  the
     predefined attribute sets are found in the
     attribute set configuration files <filename>tab/*.att</filename>. 
    </para>

    <note>
     The Zebra internal query processing is modeled after 
     the <literal>Bib1</literal> attribute set, and the non-use
     attributes type 2-6 are hard-wired in. It is therefore essential
     to be familiar with <xref linkend="querymodel-bib1-nonuse"/>. 
    </note>

    
    <sect3 id="querymodel-boolean-operators">
     <title>Boolean operators</title>
     <para>
      A pair of sub query trees, or of atomic queries, is combined
      using the standard boolean operators into new query trees.
      Thus, boolean operators are always internal nodes in the query tree.
     </para>
     
     <table id="querymodel-boolean-operators-table"
      frame="all" rowsep="1" colsep="1" align="center">

      <caption>Boolean operators</caption>
       <thead>
        <tr>
         <td>Keyword</td>
         <td>Operator</td>
         <td>Description</td>
        </tr>
      </thead>
       <tbody>
        <tr><td><literal>@and</literal></td>
         <td>binary <literal>AND</literal> operator</td>
         <td>Set intersection of two atomic queries hit sets</td>
        </tr>
        <tr><td><literal>@or</literal></td>
         <td>binary <literal>OR</literal> operator</td>
         <td>Set union of two atomic queries hit sets</td>
        </tr>
        <tr><td><literal>@not</literal></td>
         <td>binary <literal>AND NOT</literal> operator</td>
         <td>Set complement of two atomic queries hit sets</td>
        </tr>
        <tr><td><literal>@prox</literal></td>
         <td>binary <literal>PROXIMITY</literal> operator</td>
         <td>Set intersection of two atomic queries hit sets. In 
          addition, the intersection set is purged for all 
          documents which do not satisfy the requested query 
          term proximity. Usually a proper subset of the AND 
          operation.</td>
        </tr>
       </tbody>
     </table>
     
     <para>
      For example, we can combine the terms 
      <emphasis>information</emphasis> and <emphasis>retrieval</emphasis> 
      into different searches in the default index of the default
      attribute set as follows.
      Querying for the union of all documents containing the
      terms <emphasis>information</emphasis> OR
      <emphasis>retrieval</emphasis>: 
      <screen>
       Z> find @or information retrieval
      </screen>
     </para>
     <para>
      Querying for the intersection of all documents containing the
      terms <emphasis>information</emphasis> AND
      <emphasis>retrieval</emphasis>: 
      The hit set is a subset of the corresponding
      OR query.
      <screen>
       Z> find @and information retrieval
      </screen>
     </para>
     <para>
      Querying for the intersection of all documents containing the
      terms <emphasis>information</emphasis> AND
      <emphasis>retrieval</emphasis>, taking proximity into account:
      The hit set is a subset of the corresponding
      AND query        
      (see the <ulink url="&url.yaz.pqf;">PQF grammar</ulink> for
      details on the proximity operator):
      <screen>
       Z> find @prox 0 3 0 2 k 2 information retrieval
      </screen>
     </para>
     <para>
      Querying for the intersection of all documents containing the
      terms <emphasis>information</emphasis> AND
      <emphasis>retrieval</emphasis>, in the same order and near each
      other as described in the term list.  
      The hit set is a subset of the corresponding
      PROXIMITY query.
      <screen>
       Z> find "information retrieval"
      </screen>
     </para>
    </sect3>
    
    
    <sect3 id="querymodel-atomic-queries">
     <title>Atomic queries (APT)</title>
     <para>
      Atomic queries are the query parts which work on one access point
      only. These consist of <literal>an attribute list</literal>
      followed by a <literal>single term</literal> or a
      <literal>quoted term list</literal>, and are often called 
      <emphasis>Attributes-Plus-Terms (APT)</emphasis> queries.
     </para>
     <para>
      Atomic (APT) queries are always leaf nodes in the PQF query tree. 
      UN-supplied non-use attributes type 2-9 are either inherited from
      higher nodes in the query tree, or are set to Zebra's default values.
      See <xref linkend="querymodel-bib1"/> for details. 
     </para>
     
     <table id="querymodel-atomic-queries-table"
      frame="all" rowsep="1" colsep="1" align="center">

      <caption>Atomic queries (APT)</caption>
       <thead>
        <tr>
         <td>Name</td>
         <td>Type</td>
         <td>Notes</td>
        </tr>
      </thead>
       <tbody>
        <tr>
         <td><emphasis>attribute list</emphasis></td>
         <td>List of <literal>orthogonal</literal> attributes</td>
         <td>Any of the orthogonal attribute types may be omitted,
          these are inherited from higher query tree nodes, or if not
          inherited, are set to the default Zebra configuration values.
         </td>
        </tr>
        <tr>
         <td><emphasis>term</emphasis></td>
         <td>single <literal>term</literal> 
          or <literal>quoted term list</literal>   </td>
         <td>Here the search terms or list of search terms is added
          to the query</td>
        </tr>
       </tbody>
     </table>
     <para>
      Querying for the term <emphasis>information</emphasis> in the
      default index using the default attribute set, the server choice
      of access point/index, and the default non-use attributes.
      <screen>
       Z> find information
      </screen>
     </para>
     <para>
      Equivalent query fully specified including all default values:
      <screen>
       Z> find @attrset bib-1 @attr 1=1017 @attr 2=3 @attr 3=3 @attr 4=1 @attr 5=100 @attr 6=1 information
      </screen>
     </para>

     <para>
      Finding all documents which have the term
      <emphasis>debussy</emphasis> in the title field.
      <screen>
       Z> find @attr 1=4 debussy
      </screen>
     </para>

     <para>
      The <literal>scan</literal> operation is only supported with 
      atomic APT queries, as it is bound to one access point at a
      time. Boolean query trees are not allowed during
      <literal>scan</literal>.
      </para>
     
     <para>
      For example, we might want to scan the title index, starting with
      the term 
      <emphasis>debussy</emphasis>, and displaying this and the
      following terms in lexicographic order:
      <screen>
       Z> scan @attr 1=4 debussy
      </screen>
     </para>
    </sect3>
    
    
    <sect3 id="querymodel-resultset">
     <title>Named Result Sets</title>
     <para>
      Named result sets are supported in Zebra, and result sets can be
      used as operands without limitations. It follows that named
      result sets are leaf nodes in the PQF query tree, exactly as
      atomic APT queries are.
     </para>
     <para>      
      After the execution of a search, the result set is available at
      the server, such that the client can use it for subsequent
      searches or retrieval requests. The Z30.50 standard actually
      stresses the fact that result sets are volatile. It may cease
      to exist at any time point after search, and the server will
      send a diagnostic to the effect that the requested
      result set does not exist any more.
     </para>
     
     <para>
      Defining a named result set and re-using it in the next query,
      using <literal>yaz-client</literal>. Notice that the client, not
      the server, assigns the string <literal>'1'</literal> to the
      named result set. 
      <screen>
       Z> f @attr 1=4 mozart
       ...
       Number of hits: 43, setno 1
       ...
       Z> f @and @set 1 @attr 1=4 amadeus
       ...
       Number of hits: 14, setno 2
      </screen>
     </para>
     
     <note>
      Named result sets are only supported by the Z39.50 protocol.
      The SRU web service is stateless, and therefore the notion of
      named result sets does not exist when accessing a Zebra server by
      the SRU protocol.
     </note>
    </sect3>


    <sect3 id="querymodel-use-string">
     <title>Zebra's special access point of type 'string'</title>
     <para>
      The numeric <literal>use (type 1)</literal> attribute is usually 
      referred to from a given
      attribute set. In addition, Zebra let you use 
      <emphasis>any internal index
       name defined in your configuration</emphasis> 
      as use attribute value. This is a great feature for
      debugging, and when you do
      not need the complexity of defined use attribute values. It is
      the preferred way of accessing Zebra indexes directly.  
     </para>
     <para>
      Finding all documents which have the term list "information
      retrieval" in an Zebra index, using it's internal full string
      name. Scanning the same index.
      <screen>
       Z> find @attr 1=sometext "information retrieval"
       Z> scan @attr 1=sometext aterm
      </screen>
     </para>
     <para>
      Searching or scanning
      the bib-1 use attribute 54 using it's string name:
      <screen>
       Z> find @attr 1=Code-language eng
       Z> scan @attr 1=Code-language ""
      </screen>
     </para>
     <para>
      It is possible to search
      in any silly string index - if it's defined in your
      indexation rules and can be parsed by the PQF parser. 
      This is definitely not the recommended use of
      this facility, as it might confuse your users with some very
      unexpected results.
      <screen>
       Z> find @attr 1=silly/xpath/alike[@index]/name "information retrieval"
      </screen>
     </para>
     <para>
      See also <xref linkend="querymodel-pqf-apt-mapping"/> for details, and 
      <xref linkend="server-sru"/>
      for the SRU PQF query extension using string names as a fast
      debugging facility.
     </para>
    </sect3>
    
    <sect3 id="querymodel-use-xpath">
     <title>Zebra's special access point of type 'XPath' 
      for GRS filters</title>
     <para>
      As we have seen above, it is possible (albeit seldom a great
      idea) to emulate 
      <ulink url="http://www.w3.org/TR/xpath">XPath 1.0</ulink> based
      search by defining <literal>use (type 1)</literal> 
      <emphasis>string</emphasis> attributes which in appearance 
      <emphasis>resemble XPath queries</emphasis>. There are two
      problems with this approach: first, the XPath-look-alike has to
      be defined at indexation time, no new undefined
      XPath queries can entered at search time, and second, it might
      confuse users very much that an XPath-alike index name in fact
      gets populated from a possible entirely different XML element
      than it pretends to access. 
     </para>
     <para>
      When using the <literal>GRS Record Model</literal> 
      (see  <xref linkend="record-model-grs"/>), we have the
      possibility to embed <emphasis>life</emphasis> 
      XPath expressions
      in the PQF queries, which are here called
      <literal>use (type 1)</literal> <emphasis>xpath</emphasis>
      attributes. You must enable the 
      <literal>xpath enable</literal> directive in your 
      <literal>.abs</literal> configuration files. 
     </para>
     <note>
      Only a <emphasis>very</emphasis> restricted subset of the 
      <ulink url="http://www.w3.org/TR/xpath">XPath 1.0</ulink> 
      standard is supported as the GRS record model is simpler than
      a full XML DOM structure. See the following examples for 
      possibilities.
     </note>
     <para>
      Finding all documents which have the term "content" 
      inside a text node found in a specific XML DOM
      <emphasis>subtree</emphasis>, whose starting element is 
      addressed by XPath. 
      <screen>
       Z> find @attr 1=/root content 
       Z> find @attr 1=/root/first content
      </screen>
      <emphasis>Notice that the
       XPath must be absolute, i.e., must start with '/', and that the
       XPath <literal>descendant-or-self</literal> axis followed by a
       text node selection <literal>text()</literal> is implicitly
       appended to the stated XPath.
      </emphasis>
      It follows that the above searches are interpreted as:
      <screen>
       Z> find @attr 1=/root//text() content 
       Z> find @attr 1=/root/first//text() content
      </screen>
     </para>
     
     <para>
      Searching inside attribute strings is possible:
      <screen>
       Z> find @attr 1=/link/@creator morten 
      </screen>
      </para>

     <para>     
      Filter the addressing XPath by a predicate working on exact
      string values in
      attributes (in the XML sense) can be done: return all those docs which
      have the term "english" contained in one of all text sub nodes of
      the subtree defined by the XPath
      <literal>/record/title[@lang='en']</literal>. And similar
      predicate filtering.
      <screen>
       Z> find @attr 1=/record/title[@lang='en'] english
       Z> find @attr 1=/link[@creator='sisse'] sibelius
       Z> find @attr 1=/link[@creator='sisse']/description[@xml:lang='da'] sibelius 
      </screen>
     </para>
     
     <para>     
      Combining numeric indexes, boolean expressions, 
      and xpath based searches is possible:
      <screen>
       Z> find @attr 1=/record/title @and foo bar
       Z> find @and @attr 1=/record/title foo @attr 1=4 bar
      </screen> 
     </para>
     <para>
      Escaping PQF keywords and other non-parseable XPath constructs
      with <literal>'{ }'</literal> to prevent syntax errors:
      <screen>
       Z> find @attr {1=/root/first[@attr='danish']} content
       Z> find @attr {1=/record/@set} oai
      </screen>
     </para>
     <warning>
      It is worth mentioning that these dynamic performed XPath
      queries are a performance bottleneck, as no optimized
      specialized indexes can be used. Therefore, avoid the use of
      this facility when speed is essential, and the database content
      size is medium to large. 
     </warning>

    </sect3>
    
   </sect2>
   
   <sect2 id="querymodel-exp1">
    <title>Explain Attribute Set</title>
    <para>
     The Z39.50 standard defines the  
     <ulink url="&url.z39.50.explain;">Explain</ulink> attribute set
     <literal>Exp-1</literal>, which is used to discover information 
     about a server's search semantics and functional capabilities
     Zebra exposes a  "classic" 
     Explain database by base name <literal>IR-Explain-1</literal>, which
     is populated with system internal information.  
    </para>
   <para>
     The attribute-set <literal>exp-1</literal> consists of a single 
     <literal>use attribute (type 1)</literal>. 
    </para>
    <para>
     In addition, the non-Use
     <literal>bib-1</literal> attributes, that is, the types 
     <literal>Relation</literal>, <literal>Position</literal>,
     <literal>Structure</literal>, <literal>Truncation</literal>, 
     and <literal>Completeness</literal> are imported from 
     the <literal>bib-1</literal> attribute set, and may be used
     within any explain query. 
    </para>
    
    <sect3 id="querymodel-exp1-use">
    <title>Use Attributes (type = 1)</title>
     <para>
      The following Explain search attributes are supported:
      <literal>ExplainCategory</literal> (@attr 1=1), 
      <literal>DatabaseName</literal> (@attr 1=3), 
      <literal>DateAdded</literal> (@attr 1=9), 
      <literal>DateChanged</literal>(@attr 1=10).
     </para>
     <para>
      A search in the use attribute  <literal>ExplainCategory</literal>
      supports only these predefined values:
      <literal>CategoryList</literal>, <literal>TargetInfo</literal>,
      <literal>DatabaseInfo</literal>, <literal>AttributeDetails</literal>.
     </para>
     <para>
      See <filename>tab/explain.att</filename> and the 
      <ulink url="&url.z39.50;">Z39.50</ulink> standard
      for more information.
     </para>
    </sect3>
    
    <sect3>
     <title>Explain searches with yaz-client</title>
     <para>
      Classic Explain only defines retrieval of Explain information
      via ASN.1. Practically no Z39.50 clients supports this. Fortunately
      they don't have to - Zebra allows retrieval of this information
      in other formats:
      <literal>SUTRS</literal>, <literal>XML</literal>, 
      <literal>GRS-1</literal> and  <literal>ASN.1</literal> Explain.
     </para>
     
     <para>
      List supported categories to find out which explain commands are
      supported: 
      <screen>
       Z> base IR-Explain-1
       Z> find @attr exp1 1=1 categorylist
       Z> form sutrs
       Z> show 1+2
      </screen>
     </para>
     
     <para>
      Get target info, that is, investigate which databases exist at
      this server endpoint:
      <screen>
       Z> base IR-Explain-1
       Z> find @attr exp1 1=1 targetinfo
       Z> form xml
       Z> show 1+1
       Z> form grs-1
       Z> show 1+1
       Z> form sutrs
       Z> show 1+1
      </screen>
     </para>
     
     <para>
      List all supported databases, the number of hits
      is the number of databases found, which most commonly are the
      following two:
      the <literal>Default</literal> and the
      <literal>IR-Explain-1</literal> databases.
      <screen>
       Z> base IR-Explain-1
       Z> find @attr exp1 1=1 databaseinfo
       Z> form sutrs
       Z> show 1+2
      </screen>
     </para>
     
     <para>
      Get database info record for database <literal>Default</literal>.
      <screen>
       Z> base IR-Explain-1
       Z> find @and @attr exp1 1=1 databaseinfo @attr exp1 1=3 Default
      </screen>
      Identical query with explicitly specified attribute set:
      <screen>
       Z> base IR-Explain-1
       Z> find @attrset exp1 @and @attr 1=1 databaseinfo @attr 1=3 Default
      </screen>
     </para>
     
     <para>
      Get attribute details record for database
      <literal>Default</literal>.
      This query is very useful to study the internal Zebra indexes.
      If records have been indexed using the <literal>alvis</literal>
      XSLT filter, the string representation names of the known indexes can be
      found.
      <screen>
       Z> base IR-Explain-1
       Z> find @and @attr exp1 1=1 attributedetails @attr exp1 1=3 Default
      </screen>
      Identical query with explicitly specified attribute set:
      <screen>
       Z> base IR-Explain-1
       Z> find @attrset exp1 @and @attr 1=1 attributedetails @attr 1=3 Default
      </screen>
     </para>
    </sect3>
    
   </sect2>
   
   <sect2 id="querymodel-bib1">
    <title>Bib1 Attribute Set</title>
    <para>
     Most of the information contained in this section is an excerpt of
     the <literal>ATTRIBUTE SET BIB-1 (Z39.50-1995)
      SEMANTICS</literal>, 
     found at <ulink url="&url.z39.50.attset.bib1.1995;">. The BIB-1
      Attribute Set Semantics</ulink> from 1995, also in an updated 
     <ulink url="&url.z39.50.attset.bib1;">Bib-1
      Attribute Set</ulink> 
     version from 2003. Index Data is not the copyright holder of this
     information, except for the configuration details, the listing of
     Zebra's capabilities, and the example queries. 
    </para>
    
    
   <sect3 id="querymodel-bib1-use">
     <title>Use Attributes (type 1)</title>

    <para>
     A use attribute specifies an access point for any atomic query.
     These access points are highly dependent on the attribute set used
     in the query, and are user configurable using the following
     default configuration files:
     <filename>tab/bib1.att</filename>,
     <filename>tab/dan1.att</filename>,
     <filename>tab/explain.att</filename>, and
     <filename>tab/gils.att</filename>.
     New attribute sets can be added by adding new 
     <filename>tab/*.att</filename> configuration files, which need to
     be sourced in the main configuration <filename>zebra.cfg</filename>.
     </para>

    <para>
     In addition, Zebra allows the access of 
     <emphasis>internal index names</emphasis> and <emphasis>dynamic
     XPath</emphasis> as use attributes; see
      <xref linkend="querymodel-use-string"/> and 
     <xref linkend="querymodel-use-xpath"/>.
    </para> 

    <para>
     Phrase search for <emphasis>information retrieval</emphasis> in
     the title-register, scanning the same register afterwards:
     <screen>
      Z> find @attr 1=4 "information retrieval"
      Z> scan @attr 1=4 information
     </screen>
    </para>
    </sect3>

   </sect2>


   <sect2 id="querymodel-bib1-nonuse">
     <title>Zebra general Bib1 Non-Use Attributes (type 2-6)</title>
    
    <sect3 id="querymodel-bib1-relation">
     <title>Relation Attributes (type 2)</title>
     
     <para>
      Relation attributes describe the relationship of the access
      point (left side 
      of the relation) to the search term as qualified by the attributes (right
      side of the relation), e.g., Date-publication &lt;= 1975.
      </para>

     <table id="querymodel-bib1-relation-table"
      frame="all" rowsep="1" colsep="1" align="center">

      <caption>Relation Attributes (type 2)</caption>
      <thead>
        <tr>
         <td>Relation</td>
         <td>Value</td>
         <td>Notes</td>
        </tr>
       </thead>
       <tbody>
        <tr>
         <td> Less than</td>
         <td>1</td>
         <td>supported</td>
        </tr>
        <tr>
         <td>Less than or equal</td>
         <td>2</td>
         <td>supported</td>
        </tr>
        <tr>
         <td>Equal</td>
         <td>3</td>
         <td>default</td>
        </tr>
        <tr>
         <td>Greater or equal</td>
         <td>4</td>
         <td>supported</td>
        </tr>
        <tr>
         <td>Greater than</td>
         <td>5</td>
         <td>supported</td>
        </tr>
        <tr>
         <td>Not equal</td>
         <td>6</td>
         <td>unsupported</td>
        </tr>
        <tr>
         <td>Phonetic</td>
         <td>100</td>
         <td>unsupported</td>
        </tr>
        <tr>
         <td>Stem</td>
         <td>101</td>
         <td>unsupported</td>
        </tr>
        <tr>
         <td>Relevance</td>
         <td>102</td>
         <td>supported</td>
        </tr>
        <tr>
         <td>AlwaysMatches</td>
         <td>103</td>
         <td>supported</td>
        </tr>
       </tbody>
     </table>

     <para>
      The relation attributes 
      <literal>1-5</literal> are supported and work exactly as
      expected.
      All ordering operations are based on a lexicographical ordering, 
      <emphasis>expect</emphasis> when the 
      <literal>structure attribute numeric (109)</literal> is used. In
      this case, ordering is numerical. See 
      <xref linkend="querymodel-bib1-structure"/>.
      <screen>
       Z>  find @attr 1=Title @attr 2=1 music
       ...
       Number of hits: 11745, setno 1
       ...
       Z>  find @attr 1=Title @attr 2=2 music
       ...
       Number of hits: 11771, setno 2
       ...
       Z>  find @attr 1=Title @attr 2=3 music
       ...
       Number of hits: 532, setno 3
       ...
       Z>  find @attr 1=Title @attr 2=4 music
       ...
       Number of hits: 11463, setno 4
       ...
       Z>  find @attr 1=Title @attr 2=5 music
       ...
       Number of hits: 11419, setno 5
      </screen>
     </para>

     <para>
      The relation attribute 
      <literal>Relevance (102)</literal> is supported, see
      <xref linkend="administration-ranking"/> for full information.
     </para>
     
     <para>
      Ranked search for <emphasis>information retrieval</emphasis> in
      the title-register:
      <screen>
       Z> find @attr 1=4 @attr 2=102 "information retrieval"
      </screen>
     </para>

     <para>
      The relation attribute 
      <literal>AlwaysMatches (103)</literal> is in the default
      configuration
      supported in conjecture with structure attribute 
      <literal>Phrase (1)</literal> (which may be omitted by
      default). 
      It can be configured to work with other structure attributes,
      see the configuration file 
      <filename>tab/default.idx</filename> and 
       <xref linkend="querymodel-pqf-apt-mapping"/>. 
     </para>
     <para>
      <literal>AlwaysMatches (103)</literal> is a
      great way to discover how many documents have been indexed in a
      given field. The search term is ignored, but needed for correct
      PQF syntax. An empty search term may be supplied.
      <screen>
       Z> find @attr 1=Title  @attr 2=103  ""
       Z> find @attr 1=Title  @attr 2=103  @attr 4=1 ""
      </screen>
     </para>


    </sect3>

    <sect3 id="querymodel-bib1-position">
     <title>Position Attributes (type 3)</title>
 
     <para>
      The position attribute specifies the location of the search term
      within the field or subfield in which it appears.
     </para>

     <table id="querymodel-bib1-position-table"
      frame="all" rowsep="1" colsep="1" align="center">

      <caption>Position Attributes (type 3)</caption>
      <thead>
        <tr>
         <td>Position</td>
         <td>Value</td>
         <td>Notes</td>
        </tr>
       </thead>
       <tbody>
        <tr>
         <td>First in field </td>
         <td>1</td>
         <td>unsupported</td>
        </tr>
        <tr>
         <td>First in subfield</td>
         <td>2</td>
         <td>unsupported</td>
        </tr>
        <tr>
         <td>Any position in field</td>
         <td>3</td>
         <td>default</td>
        </tr>
       </tbody>
     </table>
 
    <para>
      The position attribute values <literal>first in field (1)</literal>,
      and <literal>first in subfield(2)</literal> are unsupported.
      Using them does not trigger an error, but silently defaults to 
      <literal>any position in field (3)</literal>.
      <!-- It should -->
      </para>
    </sect3>
    
    <sect3 id="querymodel-bib1-structure">
     <title>Structure Attributes (type 4)</title>
   
     <para>
      The structure attribute specifies the type of search
      term. This causes the search to be mapped on
      different Zebra internal indexes, which must have been defined
      at index time. 
     </para>

     <para> 
      The possible values of the  
      <literal>structure attribute (type 4)</literal> can be defined
      using the configuration file <filename>
      tab/default.idx</filename>.
      The default configuration is summarized in this table.
     </para>

     <table id="querymodel-bib1-structure-table"
      frame="all" rowsep="1" colsep="1" align="center">

      <caption>Structure Attributes (type 4)</caption>
      <thead>
        <tr>
         <td>Structure</td>
         <td>Value</td>
         <td>Notes</td>
        </tr>
       </thead>
       <tbody>
        <tr>
         <td>Phrase </td>
         <td>1</td>
         <td>default</td>
        </tr>
        <tr>
         <td>Word</td>
         <td>2</td>
         <td>supported</td>
        </tr>
        <tr>
         <td>Key</td>
         <td>3</td>
         <td>supported</td>
        </tr>
        <tr>
         <td>Year</td>
         <td>4</td>
         <td>supported</td>
        </tr>
        <tr>
         <td>Date (normalized)</td>
         <td>5</td>
         <td>supported</td>
        </tr>
        <tr>
         <td>Word list</td>
         <td>6</td>
         <td>supported</td>
        </tr>
        <tr>
         <td>Date (un-normalized)</td>
         <td>100</td>
         <td>unsupported</td>
        </tr>
        <tr>
         <td>Name (normalized) </td>
         <td>101</td>
         <td>unsupported</td>
        </tr>
        <tr>
         <td>Name (un-normalized) </td>
         <td>102</td>
         <td>unsupported</td>
        </tr>
        <tr>
         <td>Structure</td>
         <td>103</td>
         <td>unsupported</td>
        </tr>
        <tr>
         <td>Urx</td>
         <td>104</td>
         <td>supported</td>
        </tr>
        <tr>
         <td>Free-form-text</td>
         <td>105</td>
         <td>supported</td>
        </tr>
        <tr>
         <td>Document-text</td>
         <td>106</td>
         <td>supported</td>
        </tr>
        <tr>
         <td>Local-number</td>
         <td>107</td>
         <td>supported</td>
        </tr>
        <tr>
         <td>String</td>
         <td>108</td>
         <td>unsupported</td>
        </tr>
        <tr>
         <td>Numeric string</td>
         <td>109</td>
         <td>supported</td>
        </tr>
       </tbody>
     </table>
     

    <para>
     The structure attribute values 
     <literal>Word list (6)</literal>
     is supported, and maps to the boolean <literal>AND</literal>
     combination of words supplied. The word list is useful when
     google-like bag-of-word queries need to be translated from a GUI
     query language to PQF.  For example, the following queries
     are equivalent:
     <screen>
      Z> find @attr 1=Title @attr 4=6 "mozart amadeus"
      Z> find @attr 1=Title  @and mozart amadeus
     </screen>
    </para>

    <para>
     The structure attribute value 
     <literal>Free-form-text (105)</literal> and
     <literal>Document-text (106)</literal>
     are supported, and map both to the boolean <literal>OR</literal>
     combination of words supplied. The following queries
     are equivalent:
     <screen>
      Z> find @attr 1=Body-of-text @attr 4=105 "bach salieri teleman"
      Z> find @attr 1=Body-of-text @attr 4=106 "bach salieri teleman"
      Z> find @attr 1=Body-of-text @or bach @or salieri teleman 
     </screen>
     This <literal>OR</literal> list of terms is very useful in
     combination with relevance ranking:
     <screen>
      Z> find @attr 1=Body-of-text @attr 2=102 @attr 4=105 "bach salieri teleman"
     </screen>
    </para>
    
    <para>
     The structure attribute value 
     <literal>Local number (107)</literal>
     is supported, and maps always to the Zebra internal document ID,
     irrespectively which use attribute is specified. The following queries
     have exactly the same unique record in the hit set:
     <screen>
      Z> find @attr 4=107 10
      Z> find @attr 1=4 @attr 4=107 10
      Z> find @attr 1=1010 @attr 4=107 10
     </screen>
    </para>

    <para>
     In
     the GILS schema (<literal>gils.abs</literal>), the
     west-bounding-coordinate is indexed as type <literal>n</literal>,
     and is therefore searched by specifying
     <emphasis>structure</emphasis>=<emphasis>Numeric String</emphasis>.
     To match all those records with west-bounding-coordinate greater
     than -114 we use the following query:
     <screen>
      Z> find @attr 4=109 @attr 2=5 @attr gils 1=2038 -114
     </screen> 
    </para>
     <note>
      The exact mapping between PQF queries and Zebra internal indexes
      and index types is explained in 
       <xref linkend="querymodel-pqf-apt-mapping"/>.
      </note>

   </sect3>

    <sect3 id="querymodel-bib1-truncation">
     <title>Truncation Attributes (type = 5)</title>

     <para>
      The truncation attribute specifies whether variations of one or
      more characters are allowed between search term and hit terms, or
      not. Using non-default truncation attributes will broaden the
      document hit set of a search query.
     </para>

     <table id="querymodel-bib1-truncation-table"
      frame="all" rowsep="1" colsep="1" align="center">

      <caption>Truncation Attributes (type 5)</caption>
      <thead>
        <tr>
         <td>Truncation</td>
         <td>Value</td>
         <td>Notes</td>
        </tr>
       </thead>
       <tbody>
        <tr>
         <td>Right truncation </td>
         <td>1</td>
         <td>supported</td>
        </tr>
        <tr>
         <td>Left truncation</td>
         <td>2</td>
         <td>supported</td>
        </tr>
        <tr>
         <td>Left and right truncation</td>
         <td>3</td>
         <td>supported</td>
        </tr>
        <tr>
         <td>Do not truncate</td>
         <td>100</td>
         <td>default</td>
        </tr>
        <tr>
         <td>Process # in search term</td>
         <td>101</td>
         <td>supported</td>
        </tr>
        <tr>
         <td>RegExpr-1 </td>
         <td>102</td>
         <td>supported</td>
        </tr>
        <tr>
         <td>RegExpr-2</td>
         <td>103</td>
         <td>supported</td>
        </tr>
       </tbody>
     </table>

     <para>
      The truncation attribute values 1-3 perform the obvious way:
      <screen>
       Z> scan @attr 1=Body-of-text  schnittke
       ...
       * schnittke (81)
       schnittkes (31)
       schnittstelle (1)
       ...
       Z> find @attr 1=Body-of-text  @attr 5=1 schnittke
       ...
       Number of hits: 95, setno 7
       ...
       Z> find @attr 1=Body-of-text  @attr 5=2 schnittke
       ...
       Number of hits: 81, setno 6
       ...
       Z> find @attr 1=Body-of-text  @attr 5=3 schnittke
       ...
       Number of hits: 95, setno 8
      </screen>
      </para>

     <para>
      The truncation attribute value 
      <literal>Process # in search term (101)</literal> is a
      poor-man's regular expression search. It maps
      each <literal>#</literal> to <literal>.*</literal>, and
      performs then a <literal>Regexp-1 (102)</literal> regular
      expression search. The following two queries are equivalent:
      <screen>
       Z> find @attr 1=Body-of-text  @attr 5=101 schnit#ke
       Z> find @attr 1=Body-of-text  @attr 5=102 schnit.*ke
       ...
       Number of hits: 89, setno 10
      </screen>
     </para>
     
     <para>
      The truncation attribute value 
       <literal>Regexp-1 (102)</literal> is a normal regular search,
      see <xref linkend="querymodel-regular"/> for details.
      <screen>
       Z> find @attr 1=Body-of-text  @attr 5=102 schnit+ke
       Z> find @attr 1=Body-of-text  @attr 5=102 schni[a-t]+ke
      </screen>
     </para>

     <para>
       The truncation attribute value 
      <literal>Regexp-2 (103) </literal> is a Zebra specific extension
      which allows <emphasis>fuzzy</emphasis> matches. One single
      error in spelling of search terms is allowed, i.e., a document
      is hit if it includes a term which can be mapped to the used
      search term by one character substitution, addition, deletion or
      change of position. 
      <screen>
       Z> find @attr 1=Body-of-text  @attr 5=100 schnittke
       ...
       Number of hits: 81, setno 14
       ...
       Z> find @attr 1=Body-of-text  @attr 5=103 schnittke
       ...
       Number of hits: 103, setno 15
       ...
      </screen>
      </para>  
    </sect3>
    
    <sect3 id="querymodel-bib1-completeness">
    <title>Completeness Attributes (type = 6)</title>


     <para>
      The <literal>Completeness Attributes (type = 6)</literal>
      is used to specify that a given search term or term list is  either  
      part of the terms of a given index/field 
      (<literal>Incomplete subfield (1)</literal>), or is
      what literally is found in the entire field's index
      (<literal>Complete field (3)</literal>).
      </para>

     <table id="querymodel-bib1-completeness-table"
      frame="all" rowsep="1" colsep="1" align="center">
      <caption>Completeness Attributes (type = 6)</caption>
      <thead>
        <tr>
         <td>Completeness</td>
         <td>Value</td>
         <td>Notes</td>
        </tr>
       </thead>
       <tbody>
        <tr>
         <td>Incomplete subfield</td>
         <td>1</td>
         <td>default</td>
        </tr>
        <tr>
         <td>Complete subfield</td>
         <td>2</td>
         <td>depreciated</td>
        </tr>
        <tr>
         <td>Complete field</td>
         <td>3</td>
         <td>supported</td>
        </tr>
       </tbody>
     </table>

     <para>
      The <literal>Completeness Attributes (type = 6)</literal>
      is only partially and conditionally
      supported in the sense that it is ignored if the hit index is
      not of structure <literal>type="w"</literal> or 
      <literal>type="p"</literal>.
      </para>
     <para>
      <literal>Incomplete subfield (1)</literal> is the default, and
      makes Zebra use 
      register <literal>type="w"</literal>, whereas 
      <literal>Complete field (3)</literal> triggers
      search and scan in index <literal>type="p"</literal>.
     </para>
     <para>
      The <literal>Complete subfield (2)</literal> is a reminiscens
      from the  happy <literal>MARC</literal>
      binary format days. Zebra does not support it, but maps silently
      to <literal>Complete field (3)</literal>.
     </para>

     <note>
      The exact mapping between PQF queries and Zebra internal indexes
      and index types is explained in 
       <xref linkend="querymodel-pqf-apt-mapping"/>.
      </note>
    </sect3>
   </sect2>
  
   </sect1>


  <sect1 id="querymodel-zebra">
   <title>Advanced Zebra PQF Features</title>
   <para>
    The Zebra internal query engine has been extended to specific needs
    not covered by the <literal>bib-1</literal> attribute set query
    model. These extensions are <emphasis>non-standard</emphasis>
    and <emphasis>non-portable</emphasis>: most functional extensions
    are modeled over the <literal>bib-1</literal> attribute set,
    defining type 7-9 attributes.
    There are also the special 
    <literal>string</literal> type index names for the
    <literal>idxpath</literal> attribute set.  
   </para>
    
   <sect2 id="querymodel-zebra-attr-allrecords">
    <title>Zebra specific retrieval of all records</title>
    <para>
     Zebra defines a hardwired <literal>string</literal> index name
     called <literal>_ALLRECORDS</literal>. It matches any record
     contained in the database, if used in conjunction with 
     the relation attribute 
     <literal>AlwaysMatches (103)</literal>.
     </para>
    <para>
     The <literal>_ALLRECORDS</literal> index name is used for total database
     export. The search term is ignored, it may be empty.
     <screen>
      Z> find @attr 1=_ALLRECORDS @attr 2=103 ""
     </screen>
    </para>
    <para>
     Combination with other index types can be made. For example, to
     find all records which are <emphasis>not</emphasis> indexed in
     the <literal>Title</literal> register, issue one of the two
     equivalent queries:
     <screen>
      Z> find @not @attr 1=_ALLRECORDS @attr 2=103 "" @attr 1=Title @attr 2=103 ""
      Z> find @not @attr 1=_ALLRECORDS @attr 2=103 "" @attr 1=4 @attr 2=103 ""
     </screen>
    </para>
    <warning>
     The special string index <literal>_ALLRECORDS</literal> is
     experimental, and the provided functionality and syntax may very
     well change in future releases of Zebra.
    </warning>
    
   </sect2>

   <sect2 id="querymodel-zebra-attr-search">
    <title>Zebra specific Search Extensions to all Attribute Sets</title>
    <para>
     Zebra extends the Bib1 attribute types, and these extensions are
     recognized regardless of attribute 
     set used in a <literal>search</literal> operation query.
    </para>

     <table id="querymodel-zebra-attr-search-table"
      frame="all" rowsep="1" colsep="1" align="center">

      <caption>Zebra Search Attribute Extensions</caption>
       <thead>
        <tr>
         <td>Name</td>
         <td>Value</td>
         <td>Operation</td>
         <td>Zebra version</td>
        </tr>
      </thead>
       <tbody>
        <tr>
         <td>Embedded Sort</td>
         <td>7</td>
         <td>search</td>
         <td>1.1</td>
        </tr>
        <tr>
         <td>Term Set</td>
         <td>8</td>
         <td>search</td>
         <td>1.1</td>
        </tr>
        <tr>
         <td>Rank Weight</td>
         <td>9</td>
         <td>search</td>
         <td>1.1</td>
        </tr>
        <tr>
         <td>Approx Limit</td>
         <td>9</td>
         <td>search</td>
         <td>1.4</td>
        </tr>
        <tr>
         <td>Term Reference</td>
         <td>10</td>
         <td>search</td>
         <td>1.4</td>
        </tr>
       </tbody>
      </table>      

    <sect3 id="querymodel-zebra-attr-sorting">
     <title>Zebra Extension Embedded Sort Attribute (type 7)</title>
    </sect3>
    <para>
     The embedded sort is a way to specify sort within a query - thus
     removing the need to send a Sort Request separately. It is both
     faster and does not require clients to deal with the Sort
     Facility. 
    </para>

    <para>
     All ordering operations are based on a lexicographical ordering, 
     <emphasis>expect</emphasis> when the 
     <literal>structure attribute numeric (109)</literal> is used. In
     this case, ordering is numerical. See 
      <xref linkend="querymodel-bib1-structure"/>.
    </para>

    <para>
     The possible values after attribute <literal>type 7</literal> are
     <literal>1</literal> ascending and 
     <literal>2</literal> descending. 
     The attributes+term (APT) node is separate from the
     rest and must be <literal>@or</literal>'ed. 
     The term associated with APT is the sorting level in integers,
     where <literal>0</literal> means primary sort, 
     <literal>1</literal> means secondary sort, and so forth.
     See also <xref linkend="administration-ranking"/>.
    </para>
    <para>
     For example, searching for water, sort by title (ascending) 
     <screen>
      Z> find @or @attr 1=1016 water @attr 7=1 @attr 1=4 0
     </screen>
    </para>
    <para>
     Or, searching for water, sort by title ascending, then date descending
     <screen>
      Z> find @or @or @attr 1=1016 water @attr 7=1 @attr 1=4 0 @attr 7=2 @attr 1=30 1
     </screen>
    </para>
    
    <sect3 id="querymodel-zebra-attr-estimation">
     <title>Zebra Extension Term Set Attribute (type 8)</title>
    </sect3>
    <para>
     The Term Set feature is a facility that allows a search to store
     hitting terms in a "pseudo" resultset; thus a search (as usual) +
     a scan-like facility. Requires a client that can do named result
     sets since the search generates two result sets. The value for
     attribute 8 is the name of a result set (string). The terms in
     the named term set are returned as SUTRS records. 
    </para>
    <para>
     For example, searching  for u in title, right truncated, and
     storing the result in term set named 'aset'
     <screen> 
      Z> find @attr 5=1 @attr 1=4 @attr 8=aset u
     </screen>
    </para>
    <warning>
     The model has one serious flaw: we don't know the size of term
     set. Experimental. Do not use in production code.
    </warning>

    <sect3 id="querymodel-zebra-attr-weight">
     <title>Zebra Extension Rank Weight Attribute (type 9)</title>
    </sect3>
    <para>
     Rank weight is a way to pass a value to a ranking algorithm - so
     that one APT has one value - while another as a different one. 
     See also <xref linkend="administration-ranking"/>.
    </para>
    <para>
     For example, searching  for utah in title with weight 30 as well
     as any with weight 20: 
     <screen>  
      Z> find @attr 2=102 @or @attr 9=30 @attr 1=4 utah @attr 9=20 utah
     </screen>
    </para>

    <sect3 id="querymodel-zebra-attr-limit">
     <title>Zebra Extension Approximative Limit Attribute (type 9)</title>
    </sect3>
    <para>
     Newer Zebra versions normally estimate hit count for every APT
     (leaf) in the query tree. These hit counts are returned as part of
     the searchResult-1 facility in the binary encoded Z39.50 search
     response packages.
    </para>
    <para>
     By setting a limit for the APT we can make Zebra turn into
     approximate hit count when a certain hit count limit is
     reached. A value of zero means exact hit count.
    </para>
    <para>
     For example, we might be interested in exact hit count for a, but
     for b we allow hit count estimates for 1000 and higher. 
     <screen>
      Z> find @and a @attr 9=1000 b
     </screen>
    </para>
    <note>
     The estimated hit count facility makes searches faster, as one
     only needs to process large hit lists partially.
    </note>
    <warning>
     This facility clashes with rank weight, because there all
     documents in the hit lists need to be examined for scoring and
     re-sorting.
     It is an experimental
     extension. Do not use in production code.
    </warning>

    <sect3 id="querymodel-zebra-attr-termref">
     <title>Zebra Extension Term Reference Attribute (type 10)</title>
    </sect3>
    <para>
     Zebra supports the <literal>searchResult-1</literal> facility. 
     If the <literal>Term Reference Attribute (type 10)</literal> is
     given, that specifies a subqueryId value returned as part of the
     search result. It is a way for a client to name an APT part of a
     query. 
    </para>
    <!--
    <para>
     <screen>
     </screen>
    </para>
    -->
    <warning>
     Experimental. Do not use in production code.
    </warning>


   </sect2>
    

   <sect2 id="querymodel-zebra-attr-scan">
    <title>Zebra specific Scan Extensions to all Attribute Sets</title>
    <para>
     Zebra extends the Bib1 attribute types, and these extensions are
     recognized regardless of attribute 
     set used in a <literal>scan</literal> operation query.
    </para>
     <table id="querymodel-zebra-attr-scan-table"
      frame="all" rowsep="1" colsep="1" align="center">

      <caption>Zebra Scan Attribute Extensions</caption>
       <thead>
        <tr>
         <td>Name</td>
         <td>Type</td>
         <td>Operation</td>
         <td>Zebra version</td>
        </tr>
      </thead>
       <tbody>
        <tr>
         <td>Result Set Narrow</td>
         <td>8</td>
         <td>scan</td>
         <td>1.3</td>
        </tr>
        <tr>
         <td>Approximative Limit</td>
         <td>9</td>
         <td>scan</td>
         <td>1.4</td>
        </tr>
       </tbody>
      </table>      

    <sect3 id="querymodel-zebra-attr-narrow">
     <title>Zebra Extension Result Set Narrow (type 8)</title>
    </sect3>
    <para>
     If attribute <literal>Result Set Narrow (type 8)</literal> 
     is given for <literal>scan</literal>, the value is the name of a
     result set. Each hit count in <literal>scan</literal> is 
     <literal>@and</literal>'ed with the result set given. 
    </para>
    <para>
     Consider for example 
     the case of scanning all title fields around the
     scanterm <emphasis>mozart</emphasis>, then refining the scan by
     issuing a filtering query for <emphasis>amadeus</emphasis> to
     restrict the scan to the result set of the query:  
     <screen>
      Z> scan @attr 1=4 mozart 
      ...
      * mozart (43)
        mozartforskningen (1)
        mozartiana (1)
        mozarts (16)
      ...
      Z> f @attr 1=4 amadeus   
      ...
      Number of hits: 15, setno 2
      ...
      Z> scan @attr 1=4 @attr 8=2 mozart
      ...
      * mozart (14)
        mozartforskningen (0)
        mozartiana (0)
        mozarts (1)
      ...
     </screen>
    </para>
   
    <warning>
     Experimental. Do not use in production code.
    </warning>

    <sect3 id="querymodel-zebra-attr-approx">
     <title>Zebra Extension Approximative Limit (type 9)</title>
    </sect3>
    <para>
     The <literal>Zebra Extension Approximative Limit (type
      9)</literal> is a way to enable approximate
     hit counts for <literal>scan</literal> hit counts, in the same
     way as for <literal>search</literal> hit counts. 
    </para>
    <!--
    <para>
     <screen>
     </screen>
    </para>
    -->
    <warning>
     Experimental and buggy. Definitely not to be used in production code.
    </warning>


   </sect2>
   
   
   <sect2 id="querymodel-idxpath">
    <title>Zebra special IDXPATH Attribute Set for GRS indexing</title>
    <para>
     The attribute-set <literal>idxpath</literal> consists of a single 
     <literal>Use (type 1)</literal> attribute. All non-use attributes
     behave as normal. 
    </para>
    <para>
     This feature is enabled when defining the
     <literal>xpath enable</literal> option in the GRS filter
     <filename>*.abs</filename> configuration files. If one wants to use
     the special <literal>idxpath</literal> numeric attribute set, the
     main Zebra configuration file <filename>zebra.cfg</filename>
     directive <literal>attset: idxpath.att</literal> must be enabled.
    </para>
    <warning>The <literal>idxpath</literal> is depreciated, may not be
     supported in future Zebra versions, and should definitely
     not be used in production code.
    </warning>

    <sect3 id="querymodel-idxpath-use">
    <title>IDXPATH Use Attributes (type = 1)</title>
     <para>
      This attribute set allows one to search GRS filter indexed
      records by XPATH like structured index names. 
     </para>

     <warning>The <literal>idxpath</literal> option defines hard-coded
      index names, which might clash with your own index names.
     </warning>
     
     <table id="querymodel-idxpath-use-table"
      frame="all" rowsep="1" colsep="1" align="center">

      <caption>Zebra specific IDXPATH Use Attributes (type 1)</caption>
      <thead>
        <tr>
         <td>IDXPATH</td>
         <td>Value</td>
         <td>String Index</td>
         <td>Notes</td>
        </tr>
       </thead>
       <tbody>
        <tr>
         <td>XPATH Begin</td>
         <td>1</td>
         <td>_XPATH_BEGIN</td>
         <td>depreciated</td>
        </tr>
        <tr>
         <td>XPATH End</td>
         <td>2</td>
         <td>_XPATH_END</td>
         <td>depreciated</td>
        </tr>
        <tr>
         <td>XPATH CData</td>
         <td>1016</td>
         <td>_XPATH_CDATA</td>
         <td>depreciated</td>
        </tr>
        <tr>
         <td>XPATH Attribute Name</td>
         <td>3</td>
         <td>_XPATH_ATTR_NAME</td>
         <td>depreciated</td>
        </tr>
        <tr>
         <td>XPATH Attribute CData</td>
         <td>1015</td>
         <td>_XPATH_ATTR_CDATA</td>
         <td>depreciated</td>
        </tr>
       </tbody>
     </table>


     <para>
      See <filename>tab/idxpath.att</filename> for more information.
     </para>
     <para>
      Search for all documents starting with root element 
      <literal>/root</literal> (either using the numeric or the string
      use attributes):
      <screen>
       Z> find @attrset idxpath @attr 1=1 @attr 4=3 root/ 
       Z> find @attr idxpath 1=1 @attr 4=3 root/ 
       Z> find @attr 1=_XPATH_BEGIN @attr 4=3 root/ 
      </screen>
     </para>
     <para>
      Search for all documents where specific nested XPATH 
      <literal>/c1/c2/../cn</literal> exists. Notice the very
      counter-intuitive <emphasis>reverse</emphasis> notation!
      <screen>
       Z> find @attrset idxpath @attr 1=1 @attr 4=3 cn/cn-1/../c1/ 
       Z> find @attr 1=_XPATH_BEGIN @attr 4=3 cn/cn-1/../c1/ 
      </screen>
     </para>
     <para>
      Search for CDATA string <emphasis>text</emphasis> in any  element
      <screen>
       Z> find @attrset idxpath @attr 1=1016 text
       Z> find @attr 1=_XPATH_CDATA text
      </screen>
     </para>
     <para>
       Search for CDATA string <emphasis>anothertext</emphasis> in any
       attribute: 
      <screen> 
       Z> find @attrset idxpath @attr 1=1015 anothertext
       Z> find @attr 1=_XPATH_ATTR_CDATA anothertext
      </screen>
     </para>
     <para>
       Search for all documents with have an XML element node
       including an XML  attribute named <emphasis>creator</emphasis> 
      <screen> 
       Z> find @attrset idxpath @attr 1=3 @attr 4=3 creator 
       Z> find @attr 1=_XPATH_ATTR_NAME @attr 4=3 creator 
      </screen>
     </para>
     <para>
      Combining usual <literal>bib-1</literal> attribute set searches
      with <literal>idxpath</literal> attribute set searches:
      <screen>
       Z> find @and @attr idxpath 1=1 @attr 4=3 link/ @attr 1=4 mozart
       Z> find @and @attr 1=_XPATH_BEGIN @attr 4=3 link/ @attr 1=_XPATH_CDATA mozart
      </screen>
     </para>
     <para>
      Scanning is supported on all <literal>idxpath</literal>
      indexes, both specified as numeric use attributes, or as string
      index names. 
      <screen>
       Z> scan  @attrset idxpath @attr 1=1016 text
       Z> scan  @attr 1=_XPATH_ATTR_CDATA anothertext
       Z> scan  @attrset idxpath @attr 1=3 @attr 4=3 ''
      </screen>
     </para>

    </sect3>
   </sect2>


   <sect2 id="querymodel-pqf-apt-mapping">
    <title>Mapping from PQF atomic APT queries to Zebra internal 
     register indexes</title>
    <para>
     The rules for PQF APT mapping are rather tricky to grasp in the
     first place. We deal first with the rules for deciding which
     internal register or string index to use, according to the use
     attribute or access point specified in the query. Thereafter we
     deal with the rules for determining the correct structure type of
     the named register. 
    </para>

   <sect3 id="querymodel-pqf-apt-mapping-accesspoint">
    <title>Mapping of PQF APT access points</title>
    <para>
      Zebra understands four fundamental different types of access
      points, of which only the  
      <emphasis>numeric use attribute</emphasis> type access points
      are defined by the  <ulink url="&url.z39.50;">Z39.50</ulink>
      standard.
      All other access point types are Zebra specific, and non-portable.
    </para>

     <table id="querymodel-zebra-mapping-accesspoint-types"
      frame="all" rowsep="1" colsep="1" align="center">

      <caption>Access point name mapping</caption>
       <thead>
        <tr>
         <td>Access Point</td>
         <td>Type</td>
         <td>Grammar</td>
         <td>Notes</td>
        </tr>
      </thead>
      <tbody>
       <tr>
        <td>Use attribute</td>
        <td>numeric</td>
        <td>[1-9][1-9]*</td>
        <td>directly mapped to string index name</td>
       </tr>
       <tr>
        <td>String index name</td>
        <td>string</td>
        <td>[a-zA-Z](\-?[a-zA-Z0-9])*</td>
        <td>normalized name is used as internal string index name</td>
       </tr>
       <tr>
        <td>Zebra internal index name</td>
        <td>zebra</td>
        <td>_[a-zA-Z](_?[a-zA-Z0-9])*</td>
        <td>hardwired internal string index name</td>
       </tr>
       <tr>
        <td>XPATH special index</td>
        <td>XPath</td>
        <td>/.*</td>
        <td>special xpath search for GRS indexed records</td>
       </tr>
      </tbody>
    </table>

    <para>
     <literal>Attribute set names</literal> and 
     <literal>string index names</literal> are normalizes
     according to the following rules: all <emphasis>single</emphasis>
     hyphens <literal>'-'</literal> are stripped, and all upper case
     letters are folded to lower case.
     </para>

     <para>
      <emphasis>Numeric use attributes</emphasis> are mapped 
      to the Zebra internal
      string index according to the attribute set definition in use.
      The default attribute set is <literal>Bib-1</literal>, and may be
      omitted in the PQF query.
     </para>
     
     <para>
      According to normalization and numeric
      use attribute mapping, it follows that the following
      PQF queries are considered equivalent (assuming the default
      configuration has not been altered):
      <screen>
      Z> find  @attr 1=Body-of-text serenade
      Z> find  @attr 1=bodyoftext serenade
      Z> find  @attr 1=BodyOfText serenade
      Z> find  @attr 1=bO-d-Y-of-tE-x-t serenade
      Z> find  @attr 1=1010 serenade
      Z> find  @attrset Bib-1 @attr 1=1010 serenade
      Z> find  @attrset bib1 @attr 1=1010 serenade
      Z> find  @attrset Bib1 @attr 1=1010 serenade
      Z> find  @attrset b-I-b-1 @attr 1=1010 serenade
     </screen>
    </para>

    <para>
      The <emphasis>numerical</emphasis>
      <literal>use attributes (type 1)</literal>  
      are interpreted according to the
      attribute sets which have been loaded in the
      <literal>zebra.cfg</literal> file, and are matched against specific
      fields as specified in the <literal>.abs</literal> file which
      describes the profile of the records which have been loaded.
      If no use attribute is provided, a default of 
      <literal>Bib-1 Use Any (1016)</literal> is
      assumed.
      The predefined <literal>use attribute sets</literal>
      can be reconfigured by  tweaking the configuration files
      <filename>tab/*.att</filename>, and 
      new attribute sets can be defined by adding similar files in the
      configuration path <literal>profilePath</literal> of the server.  
    </para>

     <para>
      <literal>String indexes</literal> can be accessed directly,
      independently which attribute set is in use. These are just
      ignored. The above mentioned name normalization applies.
      <literal>String index names</literal> are defined in the
      used indexing  filter configuration files, for example in the
      <literal>GRS</literal> 
      <filename>*.abs</filename> configuration files, or in the
      <literal>alvis</literal> filter XSLT indexing stylesheets.
     </para>

     <para>
      <literal>Zebra internal indexes</literal> can be accessed directly,
      according to the same rules as the user defined
      <literal>string indexes</literal>. The only difference is that   
      <literal>Zebra internal index names</literal> are hardwired,
      all uppercase and
      must start with the character <literal>'_'</literal>. 
     </para>

     <para>
      Finally, <literal>XPATH</literal> access points are only
      available using the <literal>GRS</literal> filter for indexing.
      These access point names must start with the character
      <literal>'/'</literal>, they are <emphasis>not
      normalized</emphasis>, but passed unaltered to the Zebra internal
      XPATH engine. See <xref linkend="querymodel-use-xpath"/>.

     </para>


    </sect3>


   <sect3 id="querymodel-pqf-apt-mapping-structuretype">
     <title>Mapping of PQF APT structure and completeness to 
      register type</title>
    <para>
      Internally Zebra has in it's default configuration several
     different types of registers or indexes, whose tokenization and
      character normalization rules differ. This reflects the fact that 
      searching fundamental different tokens like dates, numbers,
      bitfields and string based text needs different rule sets. 
     </para>

     <table id="querymodel-zebra-mapping-structure-types"
      frame="all" rowsep="1" colsep="1" align="center">

      <caption>Structure and completeness mapping to register types</caption>
       <thead>
        <tr>
         <td>Structure</td>
         <td>Completeness</td>
         <td>Register type</td>
         <td>Notes</td>
        </tr>
      </thead>
      <tbody>
       <tr>
        <td>
          phrase (@attr 4=1), word (@attr 4=2), 
          word-list (@attr 4=6),
          free-form-text  (@attr 4=105), or document-text (@attr 4=106)
         </td>
        <td>Incomplete field (@attr 6=1)</td>
        <td>Word ('w')</td>
        <td>Traditional tokenized and character normalized word index</td>
       </tr>
       <tr>
        <td>
          phrase (@attr 4=1), word (@attr 4=2), 
          word-list (@attr 4=6),
          free-form-text  (@attr 4=105), or document-text (@attr 4=106)
         </td>
        <td>complete field' (@attr 6=3)</td>
        <td>Phrase ('p')</td>
        <td>Character normalized, but not tokenized index for phrase
          matches
         </td>
       </tr>
       <tr>
        <td>urx (@attr 4=104)</td>
        <td>ignored</td>
        <td>URX/URL ('u')</td>
        <td>Special index for URL web addresses</td>
       </tr>
       <tr>
        <td>numeric (@attr 4=109)</td>
        <td>ignored</td>
        <td>Numeric ('u')</td>
        <td>Special index for digital numbers</td>
       </tr>
       <tr>
        <td>key (@attr 4=3)</td>
        <td>ignored</td>
        <td>Null bitmap ('0')</td>
        <td>Used for non-tokenizated and non-normalized bit sequences</td>
       </tr>
       <tr>
        <td>year (@attr 4=4)</td>
        <td>ignored</td>
        <td>Year ('y')</td>
        <td>Non-tokenizated and non-normalized 4 digit numbers</td>
       </tr>
       <tr>
        <td>date (@attr 4=5)</td>
        <td>ignored</td>
        <td>Date ('d')</td>
        <td>Non-tokenizated and non-normalized ISO date strings</td>
       </tr>
       <tr>
        <td>ignored</td>
        <td>ignored</td>
        <td>Sort ('s')</td>
        <td>Used with special sort attribute set (@attr 7=1, @attr 7=2)</td>
       </tr>
       <tr>
        <td>overruled</td>
        <td>overruled</td>
        <td>special</td>
        <td>Internal record ID register, used whenever 
         Relation Always Matches (@attr 2=103) is specified</td>
       </tr>
      </tbody>
    </table>

     <!-- see in util/zebramap.c -->
        
    <para>
     If a <emphasis>Structure</emphasis> attribute of
     <emphasis>Phrase</emphasis> is used in conjunction with a
     <emphasis>Completeness</emphasis> attribute of
     <emphasis>Complete (Sub)field</emphasis>, the term is matched
     against the contents of the phrase (long word) register, if one
     exists for the given <emphasis>Use</emphasis> attribute.
     A phrase register is created for those fields in the
     GRS <filename>*.abs</filename> file that contains a
     <literal>p</literal>-specifier.
      <screen>
       Z>  scan @attr 1=Title @attr 4=1 @attr 6=3 beethoven 
       ...
       bayreuther festspiele (1)
       * beethoven bibliography database (1)
       benny carter (1)
       ...
       Z> find @attr 1=Title @attr 4=1 @attr 6=3 "beethoven bibliography" 
       ...
       Number of hits: 0, setno 5
       ...
       Z> find @attr 1=Title @attr 4=1 @attr 6=3 "beethoven bibliography database" 
       ...
       Number of hits: 1, setno 6
       </screen>
    </para>

    <para>
     If <emphasis>Structure</emphasis>=<emphasis>Phrase</emphasis> is
     used in conjunction with <emphasis>Incomplete Field</emphasis> - the
     default value for <emphasis>Completeness</emphasis>, the
     search is directed against the normal word registers, but if the term
     contains multiple words, the term will only match if all of the words
     are found immediately adjacent, and in the given order.
     The word search is performed on those fields that are indexed as
     type <literal>w</literal> in the GRS <filename>*.abs</filename> file.
      <screen>
       Z>  scan @attr 1=Title @attr 4=1 @attr 6=1 beethoven 
       ...
         beefheart (1)
       * beethoven (18)
         beethovens (7)
       ...
       Z> find @attr 1=Title @attr 4=1 @attr 6=1 beethoven 
       ...
       Number of hits: 18, setno 1
       ...
       Z> find @attr 1=Title @attr 4=1 @attr 6=1 "beethoven  bibliography"
       ...
       Number of hits: 2, setno 2
       ...
     </screen>
    </para>

    <para>
     If the <emphasis>Structure</emphasis> attribute is
     <emphasis>Word List</emphasis>,
     <emphasis>Free-form Text</emphasis>, or
     <emphasis>Document Text</emphasis>, the term is treated as a
     natural-language, relevance-ranked query.
     This search type uses the word register, i.e. those fields
     that are indexed as type <literal>w</literal> in the
     GRS <filename>*.abs</filename> file.
    </para>

    <para>
     If the <emphasis>Structure</emphasis> attribute is
     <emphasis>Numeric String</emphasis> the term is treated as an integer.
     The search is performed on those fields that are indexed
     as type <literal>n</literal> in the GRS 
      <filename>*.abs</filename> file.
    </para>

    <para>
     If the <emphasis>Structure</emphasis> attribute is
     <emphasis>URX</emphasis> the term is treated as a URX (URL) entity.
     The search is performed on those fields that are indexed as type
     <literal>u</literal> in the <filename>*.abs</filename> file.
    </para>

    <para>
     If the <emphasis>Structure</emphasis> attribute is
     <emphasis>Local Number</emphasis> the term is treated as
     native Zebra Record Identifier.
    </para>

    <para>
     If the <emphasis>Relation</emphasis> attribute is
     <emphasis>Equals</emphasis> (default), the term is matched
     in a normal fashion (modulo truncation and processing of
     individual words, if required).
     If <emphasis>Relation</emphasis> is <emphasis>Less Than</emphasis>,
     <emphasis>Less Than or Equal</emphasis>,
     <emphasis>Greater than</emphasis>, or <emphasis>Greater than or
      Equal</emphasis>, the term is assumed to be numerical, and a
     standard regular expression is constructed to match the given
     expression.
     If <emphasis>Relation</emphasis> is <emphasis>Relevance</emphasis>,
     the standard natural-language query processor is invoked.
    </para>

    <para>
     For the <emphasis>Truncation</emphasis> attribute,
     <emphasis>No Truncation</emphasis> is the default.
     <emphasis>Left Truncation</emphasis> is not supported.
     <emphasis>Process # in search term</emphasis> is supported, as is
     <emphasis>Regxp-1</emphasis>.
     <emphasis>Regxp-2</emphasis> enables the fault-tolerant (fuzzy)
     search. As a default, a single error (deletion, insertion, 
     replacement) is accepted when terms are matched against the register
     contents.
    </para>

     </sect3>
   </sect2>

   <sect2  id="querymodel-regular">
    <title>Zebra Regular Expressions in Truncation Attribute (type = 5)</title>
    
    <para>
     Each term in a query is interpreted as a regular expression if
     the truncation value is either <emphasis>Regxp-1 (@attr 5=102)</emphasis>
     or <emphasis>Regxp-2 (@attr 5=103)</emphasis>.
     Both query types follow the same syntax with the operands:
    </para>

     <table id="querymodel-regular-operands-table"
      frame="all" rowsep="1" colsep="1" align="center">

      <caption>Regular Expression Operands</caption>
       <!--
       <thead>
       <tr><td>one</td><td>two</td></tr>
      </thead>
       -->
       <tbody>
        <tr>
         <td><literal>x</literal></td>
         <td>Matches the character <literal>x</literal>.</td>
        </tr>
        <tr>
         <td><literal>.</literal></td>
         <td>Matches any character.</td>
        </tr>
        <tr>
         <td><literal>[ .. ]</literal></td>
         <td>Matches the set of characters specified;
         such as <literal>[abc]</literal> or <literal>[a-c]</literal>.</td>
        </tr>
       </tbody>
      </table>      

    <para>
     The above operands can be combined with the following operators:
    </para>

     <table id="querymodel-regular-operators-table"
      frame="all" rowsep="1" colsep="1" align="center">
      <caption>Regular Expression Operators</caption>
       <!--
       <thead>
       <tr><td>one</td><td>two</td></tr>
      </thead>
       -->
       <tbody>
        <tr>
         <td><literal>x*</literal></td>
         <td>Matches <literal>x</literal> zero or more times. 
          Priority: high.</td>
        </tr>
        <tr>
         <td><literal>x+</literal></td>
         <td>Matches <literal>x</literal> one or more times. 
          Priority: high.</td>
        </tr>
        <tr>
         <td><literal>x?</literal></td>
         <td> Matches <literal>x</literal> zero or once. 
          Priority: high.</td>
        </tr>
        <tr>
         <td><literal>xy</literal></td>
         <td> Matches <literal>x</literal>, then <literal>y</literal>.
         Priority: medium.</td>
        </tr>
        <tr>
         <td><literal>x|y</literal></td>
         <td> Matches either <literal>x</literal> or <literal>y</literal>.
         Priority: low.</td>
        </tr>
        <tr>
         <td><literal>( )</literal></td>
         <td>The order of evaluation may be changed by using parentheses.</td>
        </tr>
       </tbody>
      </table>      

    <para>
     If the first character of the <literal>Regxp-2</literal> query
     is a plus character (<literal>+</literal>) it marks the
     beginning of a section with non-standard specifiers.
     The next plus character marks the end of the section.
     Currently Zebra only supports one specifier, the error tolerance,
     which consists one digit. 
     <!-- TODO Nice thing, but what does
     that error tolerance digit *mean*? Maybe an example would be nice? -->
    </para>

    <para>
     Since the plus operator is normally a suffix operator the addition to
     the query syntax doesn't violate the syntax for standard regular
     expressions.
    </para>

    <para>
     For example, a phrase search with regular expressions  in
     the title-register is performed like this:
     <screen>
      Z> find @attr 1=4 @attr 5=102 "informat.* retrieval"
     </screen>
    </para>

    <para>
     Combinations with other attributes are possible. For example, a
     ranked search with a regular expression:
     <screen>
      Z> find @attr 1=4 @attr 5=102 @attr 2=102 "informat.* retrieval"
     </screen>
    </para>
   </sect2>

  
   <!--
   <para>
    The RecordType parameter in the <literal>zebra.cfg</literal> file, or
    the <literal>-t</literal> option to the indexer tells Zebra how to
    process input records.
    Two basic types of processing are available - raw text and structured
    data. Raw text is just that, and it is selected by providing the
    argument <literal>text</literal> to Zebra. Structured records are
    all handled internally using the basic mechanisms described in the
    subsequent sections.
    Zebra can read structured records in many different formats.
   </para>
   -->
  </sect1>


  <sect1 id="querymodel-cql-to-pqf">
   <title>Server Side CQL to PQF Query Translation</title>
   <para>
    Using the
    <literal>&lt;cql2rpn&gt;l2rpn.txt&lt;/cql2rpn&gt;</literal>
      YAZ Frontend Virtual
    Hosts option, one can configure
    the YAZ Frontend CQL-to-PQF
    converter, specifying the interpretation of various 
    <ulink url="&url.cql;">CQL</ulink>
    indexes, relations, etc. in terms of Type-1 query attributes.
    <!-- The  yaz-client config file -->  
   </para>
   <para>
    For example, using server-side CQL-to-PQF conversion, one might
    query a zebra server like this:
    <screen>
    <![CDATA[
     yaz-client localhost:9999
     Z> querytype cql
     Z> find text=(plant and soil)
     ]]>
    </screen>
     and - if properly configured - even static relevance ranking can
     be performed using CQL query syntax:
    <screen>
    <![CDATA[
     Z> find text = /relevant (plant and soil)
     ]]>
     </screen>
   </para>

   <para>
    By the way, the same configuration can be used to 
    search using client-side CQL-to-PQF conversion:
    (the only difference is <literal>querytype cql2rpn</literal> 
    instead of 
    <literal>querytype cql</literal>, and the call specifying a local
    conversion file)
    <screen>
    <![CDATA[
     yaz-client -q local/cql2pqf.txt localhost:9999
     Z> querytype cql2rpn
     Z> find text=(plant and soil)
     ]]>
     </screen>
   </para>

   <para>
    Exhaustive information can be found in the
    Section "Specification of CQL to RPN mappings" in the YAZ manual.
    <ulink url="http://www.indexdata.dk/yaz/doc/tools.tkl#tools.cql.map">
     http://www.indexdata.dk/yaz/doc/tools.tkl#tools.cql.map</ulink>,
   and shall therefore not be repeated here.
   </para> 
  <!-- 
  <para>
    See 
      <ulink url="http://www.loc.gov/z3950/agency/zing/cql/dc-indexes.html">
      http://www.loc.gov/z3950/agency/zing/cql/dc-indexes.html</ulink>
    for the Maintenance Agency's work-in-progress mapping of Dublin Core
    indexes to Attribute Architecture (util, XD and BIB-2)
    attributes.
   </para>
   -->
 </sect1>



</chapter>

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