<chapter id="querymodel">
  <title>Query Model</title>

  <section id="querymodel-overview">
   <title>Query Model Overview</title>

   <section 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;">&acro.z3950;</ulink> and
     <ulink url="&url.sru;">&acro.sru;</ulink>,
     and implement the
     type-1 Reverse Polish Notation (&acro.rpn;) query
     model defined there.
     Unfortunately, this model has only defined a binary
     encoded representation, which is used as transport packaging in
     the &acro.z3950; protocol layer. This representation is not human
     readable, nor defines any convenient way to specify queries.
    </para>
    <para>
     Since the type-1 (&acro.rpn;)
     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>


    <section id="querymodel-query-languages-pqf">
     <title>Prefix Query Format (&acro.pqf;)</title>
     <para>
      Index Data has defined a textual representation in the
      <ulink url="&url.yaz.pqf;">Prefix Query Format</ulink>, short
      <emphasis>&acro.pqf;</emphasis>, which maps
      one-to-one to binary encoded
      <emphasis>type-1 &acro.rpn;</emphasis> queries.
      &acro.pqf; has been adopted by other
      parties developing &acro.z3950; software, and is often referred to as
      <emphasis>Prefix Query Notation</emphasis>, or in short
      &acro.pqn;. See
      <xref linkend="querymodel-rpn"/> for further explanations and
      descriptions of &zebra;'s capabilities.
     </para>
    </section>

    <section id="querymodel-query-languages-cql">
     <title>Common Query Language (&acro.cql;)</title>
     <para>
      The query model of the type-1 &acro.rpn;,
      expressed in &acro.pqf;/&acro.pqn; is natively supported.
      On the other hand, the default &acro.sru;
      web services <emphasis>Common Query Language</emphasis>
      <ulink url="&url.cql;">&acro.cql;</ulink> is not natively supported.
     </para>
     <para>
      &zebra; can be configured to understand and map &acro.cql; to &acro.pqf;. See
      <xref linkend="querymodel-cql-to-pqf"/>.
     </para>
    </section>

   </section>

   <section id="querymodel-operation-types">
    <title>Operation types</title>
    <para>
     &zebra; supports all of the three different
     &acro.z3950;/&acro.sru; operations defined in the
     standards: explain, search,
     and scan. A short description of the
     functionality and purpose of each is quite in order here.
    </para>

    <section id="querymodel-operation-type-explain">
     <title>Explain Operation</title>
     <para>
      The <emphasis>syntax</emphasis> of &acro.z3950;/&acro.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
      explain 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 &acro.z3950; embeds the explain operation
      by performing a
      search in the magic
      <literal>IR-Explain-1</literal> database;
      see <xref linkend="querymodel-exp1"/>.
     </para>
     <para>
      In &acro.sru;, explain is an entirely  separate
      operation, which returns an ZeeRex &acro.xml; record according to the
      structure defined by the protocol.
     </para>
     <para>
      In both cases, the information gathered through
      explain operations can be used to
      auto-configure a client user interface to the servers
      capabilities.
     </para>
    </section>

    <section 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 &acro.z3950;/&acro.sru; servers.
     </para>
    </section>

    <section id="querymodel-operation-type-scan">
     <title>Scan Operation</title>
     <para>
      The scan 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 scan
      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>
    </section>

   </section>

  </section>

  <section id="querymodel-rpn">
   <title>&acro.rpn; queries and semantics</title>
   <para>
    The <ulink url="&url.yaz.pqf;">&acro.pqf; grammar</ulink>
    is documented in the &yaz; manual, and shall not be
    repeated here. This textual &acro.pqf; representation
    is not transmitted to &zebra; during search, but it is in the
    client mapped to the equivalent &acro.z3950; binary
    query parse tree.
   </para>

   <section id="querymodel-rpn-tree">
    <title>&acro.rpn; tree structure</title>
    <para>
     The &acro.rpn; parse tree - or the equivalent textual representation in &acro.pqf; -
     may start with one specification of the
     <emphasis>attribute set</emphasis> used. Following is a query
     tree, which
     consists of <emphasis>atomic query parts (&acro.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>

    <section 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="top">
      <title>Attribute sets predefined in &zebra;</title>
      <tgroup cols="4">
       <thead>
	<row>
         <entry>Attribute set</entry>
         <entry>&acro.pqf; notation (Short hand)</entry>
         <entry>Status</entry>
         <entry>Notes</entry>
        </row>
       </thead>

       <tbody>
        <row>
         <entry>Explain</entry>
         <entry><literal>exp-1</literal></entry>
         <entry>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.</entry>
         <entry>predefined</entry>
        </row>
        <row>
         <entry>&acro.bib1;</entry>
         <entry><literal>bib-1</literal></entry>
         <entry>Standard &acro.pqf; query language attribute set which defines the
          semantics of &acro.z3950; searching. In addition, all of the
          non-use attributes (types 2-14) define the hard-wired
          &zebra; internal query
          processing.</entry>
         <entry>default</entry>
        </row>
        <row>
         <entry>GILS</entry>
         <entry><literal>gils</literal></entry>
         <entry>Extension to the &acro.bib1; attribute set.</entry>
         <entry>predefined</entry>
        </row>
       </tbody>
      </tgroup>
     </table>

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

     <note>
      <para>
       The &zebra; internal query processing is modeled after
       the &acro.bib1; 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"/>.
      </para>
     </note>

    </section>

    <section 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="top">
      <title>Boolean operators</title>
      <tgroup cols="3">
       <thead>
	<row>
	 <entry>Keyword</entry>
	 <entry>Operator</entry>
	 <entry>Description</entry>
	</row>
       </thead>
       <tbody>
	<row><entry><literal>@and</literal></entry>
	 <entry>binary AND operator</entry>
	 <entry>Set intersection of two atomic queries hit sets</entry>
	</row>
	<row><entry><literal>@or</literal></entry>
	 <entry>binary OR operator</entry>
	 <entry>Set union of two atomic queries hit sets</entry>
	</row>
	<row><entry><literal>@not</literal></entry>
	 <entry>binary AND NOT operator</entry>
	 <entry>Set complement of two atomic queries hit sets</entry>
	</row>
	<row><entry><literal>@prox</literal></entry>
	 <entry>binary PROXIMITY operator</entry>
	 <entry>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.</entry>
	</row>
       </tbody>
      </tgroup>
     </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;">&acro.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>
    </section>


    <section id="querymodel-atomic-queries">
     <title>Atomic queries (&acro.apt;)</title>
     <para>
      Atomic queries are the query parts which work on one access point
      only. These consist of <emphasis>an attribute list</emphasis>
      followed by a <emphasis>single term</emphasis> or a
      <emphasis>quoted term list</emphasis>, and are often called
      <emphasis>Attributes-Plus-Terms (&acro.apt;)</emphasis> queries.
     </para>
     <para>
      Atomic (&acro.apt;) queries are always leaf nodes in the &acro.pqf; query tree.
      UN-supplied non-use attributes types 2-12 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="top">
      <title>Atomic queries (&acro.apt;)</title>
      <tgroup cols="3">
       <thead>
        <row>
         <entry>Name</entry>
         <entry>Type</entry>
         <entry>Notes</entry>
        </row>
       </thead>
       <tbody>
        <row>
         <entry><emphasis>attribute list</emphasis></entry>
         <entry>List of <emphasis>orthogonal</emphasis> attributes</entry>
         <entry>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.
         </entry>
        </row>
        <row>
         <entry><emphasis>term</emphasis></entry>
         <entry>single <emphasis>term</emphasis>
          or <emphasis>quoted term list</emphasis>   </entry>
         <entry>Here the search terms or list of search terms is added
          to the query</entry>
        </row>
       </tbody>
      </tgroup>
     </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 <emphasis>scan</emphasis> operation is only supported with
      atomic &acro.apt; queries, as it is bound to one access point at a
      time. Boolean query trees are not allowed during
      <emphasis>scan</emphasis>.
     </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>
    </section>


    <section 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 &acro.pqf; query tree, exactly as
      atomic &acro.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 <application>yaz-client</application>. Notice that the client, not
      the server, assigns the string '1' 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>
      <para>
       Named result sets are only supported by the &acro.z3950; protocol.
       The &acro.sru; web service is stateless, and therefore the notion of
       named result sets does not exist when accessing a &zebra; server by
       the &acro.sru; protocol.
      </para>
     </note>
    </section>

    <section id="querymodel-use-string">
     <title>&zebra;'s special access point of type 'string'</title>
     <para>
      The numeric <emphasis>use (type 1)</emphasis> 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 its 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 its 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
      indexing rules and can be parsed by the &acro.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="zebrasrv-sru"/>
      for the &acro.sru; &acro.pqf; query extension using string names as a fast
      debugging facility.
     </para>
    </section>

    <section id="querymodel-use-xpath">
     <title>&zebra;'s special access point of type 'XPath'
      for &acro.grs1; 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 <emphasis>use (type 1)</emphasis>
      <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 indexing 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 &acro.xml; element
      than it pretends to access.
     </para>
     <para>
      When using the &acro.grs1; Record Model
      (see  <xref linkend="grs"/>), we have the
      possibility to embed <emphasis>life</emphasis>
      XPath expressions
      in the &acro.pqf; queries, which are here called
      <emphasis>use (type 1)</emphasis> <emphasis>xpath</emphasis>
      attributes. You must enable the
      <literal>xpath enable</literal> directive in your
      <literal>.abs</literal> configuration files.
     </para>
     <note>
      <para>
       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 &acro.grs1; record model is simpler than
       a full &acro.xml; &acro.dom; structure. See the following examples for
       possibilities.
      </para>
     </note>
     <para>
      Finding all documents which have the term "content"
      inside a text node found in a specific &acro.xml; &acro.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 &acro.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 &acro.pqf; keywords and other non-parseable XPath constructs
      with <literal>'{ }'</literal> to prevent client-side &acro.pqf; parsing
      syntax errors:
      <screen>
       Z> find @attr {1=/root/first[@attr='danish']} content
       Z> find @attr {1=/record/@set} oai
      </screen>
     </para>
     <warning>
      <para>
       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.
      </para>
     </warning>
    </section>
   </section>

   <section id="querymodel-exp1">
    <title>Explain Attribute Set</title>
    <para>
     The &acro.z3950; standard defines the
     <ulink url="&url.z39.50.explain;">Explain</ulink> attribute set
     Exp-1, 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
     use attribute (type 1).
    </para>
    <para>
     In addition, the non-Use
     &acro.bib1; attributes, that is, the types
     <emphasis>Relation</emphasis>, <emphasis>Position</emphasis>,
     <emphasis>Structure</emphasis>, <emphasis>Truncation</emphasis>,
     and <emphasis>Completeness</emphasis> are imported from
     the &acro.bib1; attribute set, and may be used
     within any explain query.
    </para>

    <section 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;">&acro.z3950;</ulink> standard
      for more information.
     </para>
    </section>

    <section id="querymodel-examples">
     <title>Explain searches with yaz-client</title>
     <para>
      Classic Explain only defines retrieval of Explain information
      via ASN.1. Practically no &acro.z3950; clients supports this. Fortunately
      they don't have to - &zebra; allows retrieval of this information
      in other formats:
      &acro.sutrs;, &acro.xml;,
      &acro.grs1; 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>
      &acro.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>
    </section>

   </section>

   <section id="querymodel-bib1">
    <title>&acro.bib1; Attribute Set</title>
    <para>
     Most of the information contained in this section is an excerpt of
     the ATTRIBUTE SET &acro.bib1; (&acro.z3950;-1995) SEMANTICS
     found at <ulink url="&url.z39.50.attset.bib1.1995;">. The &acro.bib1;
      Attribute Set Semantics</ulink> from 1995, also in an updated
     <ulink url="&url.z39.50.attset.bib1;">&acro.bib1;
      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>


    <section 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>.
     </para>
     <para>
      For example, some few &acro.bib1; use
      attributes from the  <filename>tab/bib1.att</filename> are:
      <screen>
       att 1               Personal-name
       att 2               Corporate-name
       att 3               Conference-name
       att 4               Title
       ...
       att 1009            Subject-name-personal
       att 1010            Body-of-text
       att 1011            Date/time-added-to-db
       ...
       att 1016            Any
       att 1017            Server-choice
       att 1018            Publisher
       ...
       att 1035            Anywhere
       att 1036            Author-Title-Subject
      </screen>
     </para>
     <para>
      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>
    </section>

   </section>


   <section id="querymodel-bib1-nonuse">
    <title>&zebra; general Bib1 Non-Use Attributes (type 2-6)</title>

    <section 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="top">
      <title>Relation Attributes (type 2)</title>
      <tgroup cols="3">
       <thead>
        <row>
         <entry>Relation</entry>
         <entry>Value</entry>
         <entry>Notes</entry>
        </row>
       </thead>
       <tbody>
        <row>
         <entry>Less than</entry>
         <entry>1</entry>
         <entry>supported</entry>
        </row>
        <row>
         <entry>Less than or equal</entry>
         <entry>2</entry>
         <entry>supported</entry>
        </row>
        <row>
         <entry>Equal</entry>
         <entry>3</entry>
         <entry>default</entry>
        </row>
        <row>
         <entry>Greater or equal</entry>
         <entry>4</entry>
         <entry>supported</entry>
        </row>
        <row>
         <entry>Greater than</entry>
         <entry>5</entry>
         <entry>supported</entry>
        </row>
        <row>
         <entry>Not equal</entry>
         <entry>6</entry>
         <entry>unsupported</entry>
        </row>
        <row>
         <entry>Phonetic</entry>
         <entry>100</entry>
         <entry>unsupported</entry>
        </row>
        <row>
         <entry>Stem</entry>
         <entry>101</entry>
         <entry>unsupported</entry>
        </row>
        <row>
         <entry>Relevance</entry>
         <entry>102</entry>
         <entry>supported</entry>
        </row>
        <row>
         <entry>AlwaysMatches</entry>
         <entry>103</entry>
         <entry>supported *</entry>
        </row>
       </tbody>
      </tgroup>
     </table>
     <note>
      <para>
       AlwaysMatches searches are only supported if alwaysmatches indexing
       has been enabled. See <xref linkend="default-idx-file"/>
      </para>
     </note>

     <para>
      The relation attributes 1-5 are supported and work exactly as
      expected.
      All ordering operations are based on a lexicographical ordering,
      <emphasis>except</emphasis> when the
      structure attribute numeric (109) 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
      <emphasis>Relevance (102)</emphasis> 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
      <emphasis>AlwaysMatches (103)</emphasis> is in the default
      configuration
      supported in conjecture with structure attribute
      <emphasis>Phrase (1)</emphasis> (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>
      <emphasis>AlwaysMatches (103)</emphasis> 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
      &acro.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>


    </section>

    <section 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="top">
      <title>Position Attributes (type 3)</title>
      <tgroup cols="3">
       <thead>
        <row>
         <entry>Position</entry>
         <entry>Value</entry>
         <entry>Notes</entry>
        </row>
       </thead>
       <tbody>
        <row>
         <entry>First in field </entry>
         <entry>1</entry>
         <entry>supported *</entry>
        </row>
        <row>
         <entry>First in subfield</entry>
         <entry>2</entry>
         <entry>supported *</entry>
        </row>
        <row>
         <entry>Any position in field</entry>
         <entry>3</entry>
         <entry>default</entry>
        </row>
       </tbody>
      </tgroup>
     </table>

     <note>
      <para>
       &zebra; only supports first-in-field seaches if the
       <literal>firstinfield</literal> is enabled for the index
       Refer to <xref linkend="default-idx-file"/>.
       &zebra; does not distinguish between first in field and
       first in subfield. They result in the same hit count.
       Searching for first position in (sub)field in only supported in &zebra;
       2.0.2 and later.
      </para>
     </note>
    </section>

    <section 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="top">
      <title>Structure Attributes (type 4)</title>
      <tgroup cols="3">
       <thead>
        <row>
         <entry>Structure</entry>
         <entry>Value</entry>
         <entry>Notes</entry>
        </row>
       </thead>
       <tbody>
        <row>
         <entry>Phrase </entry>
         <entry>1</entry>
         <entry>default</entry>
        </row>
        <row>
         <entry>Word</entry>
         <entry>2</entry>
         <entry>supported</entry>
        </row>
        <row>
         <entry>Key</entry>
         <entry>3</entry>
         <entry>supported</entry>
        </row>
        <row>
         <entry>Year</entry>
         <entry>4</entry>
         <entry>supported</entry>
        </row>
        <row>
         <entry>Date (normalized)</entry>
         <entry>5</entry>
         <entry>supported</entry>
        </row>
        <row>
         <entry>Word list</entry>
         <entry>6</entry>
         <entry>supported</entry>
        </row>
        <row>
         <entry>Date (un-normalized)</entry>
         <entry>100</entry>
         <entry>unsupported</entry>
        </row>
        <row>
         <entry>Name (normalized) </entry>
         <entry>101</entry>
         <entry>unsupported</entry>
        </row>
        <row>
         <entry>Name (un-normalized) </entry>
         <entry>102</entry>
         <entry>unsupported</entry>
        </row>
        <row>
         <entry>Structure</entry>
         <entry>103</entry>
         <entry>unsupported</entry>
        </row>
        <row>
         <entry>Urx</entry>
         <entry>104</entry>
         <entry>supported</entry>
        </row>
        <row>
         <entry>Free-form-text</entry>
         <entry>105</entry>
         <entry>supported</entry>
        </row>
        <row>
         <entry>Document-text</entry>
         <entry>106</entry>
         <entry>supported</entry>
        </row>
        <row>
         <entry>Local-number</entry>
         <entry>107</entry>
         <entry>supported</entry>
        </row>
        <row>
         <entry>String</entry>
         <entry>108</entry>
         <entry>unsupported</entry>
        </row>
        <row>
         <entry>Numeric string</entry>
         <entry>109</entry>
         <entry>supported</entry>
        </row>
       </tbody>
      </tgroup>
     </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 &acro.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>
      <para>
       The exact mapping between &acro.pqf; queries and &zebra; internal indexes
       and index types is explained in
       <xref linkend="querymodel-pqf-apt-mapping"/>.
      </para>
     </note>
    </section>


    <section 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="top">
      <title>Truncation Attributes (type 5)</title>
      <tgroup cols="3">
       <thead>
        <row>
         <entry>Truncation</entry>
         <entry>Value</entry>
         <entry>Notes</entry>
        </row>
       </thead>
       <tbody>
        <row>
         <entry>Right truncation </entry>
         <entry>1</entry>
         <entry>supported</entry>
        </row>
        <row>
         <entry>Left truncation</entry>
         <entry>2</entry>
         <entry>supported</entry>
        </row>
        <row>
         <entry>Left and right truncation</entry>
         <entry>3</entry>
         <entry>supported</entry>
        </row>
        <row>
         <entry>Do not truncate</entry>
         <entry>100</entry>
         <entry>default</entry>
        </row>
        <row>
         <entry>Process # in search term</entry>
         <entry>101</entry>
         <entry>supported</entry>
        </row>
        <row>
         <entry>RegExpr-1 </entry>
         <entry>102</entry>
         <entry>supported</entry>
        </row>
        <row>
         <entry>RegExpr-2</entry>
         <entry>103</entry>
         <entry>supported</entry>
        </row>
       </tbody>
      </tgroup>
     </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>
    </section>

    <section 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="top">
      <title>Completeness Attributes (type = 6)</title>
      <tgroup cols="3">
       <thead>
        <row>
         <entry>Completeness</entry>
         <entry>Value</entry>
         <entry>Notes</entry>
        </row>
       </thead>
       <tbody>
        <row>
         <entry>Incomplete subfield</entry>
         <entry>1</entry>
         <entry>default</entry>
        </row>
        <row>
         <entry>Complete subfield</entry>
         <entry>2</entry>
         <entry>deprecated</entry>
        </row>
        <row>
         <entry>Complete field</entry>
         <entry>3</entry>
         <entry>supported</entry>
        </row>
       </tbody>
      </tgroup>
     </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 reminiscent
      from the  happy &acro.marc;
      binary format days. &zebra; does not support it, but maps silently
      to <literal>Complete field (3)</literal>.
     </para>

     <note>
      <para>
       The exact mapping between &acro.pqf; queries and &zebra; internal indexes
       and index types is explained in
       <xref linkend="querymodel-pqf-apt-mapping"/>.
      </para>
     </note>
    </section>

   </section>

  </section>

  <section id="querymodel-zebra">
   <title>Extended &zebra; &acro.rpn; 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 and higher values.
    There are also the special
    <literal>string</literal> type index names for the
    <literal>idxpath</literal> attribute set.
   </para>

   <section 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>
     <para>
      The special string index <literal>_ALLRECORDS</literal> is
      experimental, and the provided functionality and syntax may very
      well change in future releases of &zebra;.
     </para>
    </warning>
   </section>

   <section id="querymodel-zebra-attr-search">
    <title>&zebra; specific Search Extensions to all Attribute Sets</title>
    <para>
     &zebra; extends the &acro.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="top">
     <title>&zebra; Search Attribute Extensions</title>
     <tgroup cols="4">
      <thead>
       <row>
	<entry>Name</entry>
	<entry>Value</entry>
	<entry>Operation</entry>
	<entry>&zebra; version</entry>
       </row>
      </thead>
      <tbody>
       <row>
	<entry>Embedded Sort</entry>
	<entry>7</entry>
	<entry>search</entry>
	<entry>1.1</entry>
       </row>
       <row>
	<entry>Term Set</entry>
	<entry>8</entry>
	<entry>search</entry>
	<entry>1.1</entry>
       </row>
       <row>
	<entry>Rank Weight</entry>
	<entry>9</entry>
	<entry>search</entry>
	<entry>1.1</entry>
       </row>
       <row>
	<entry>Term Reference</entry>
	<entry>10</entry>
	<entry>search</entry>
	<entry>1.4</entry>
       </row>
       <row>
	<entry>Local Approx Limit</entry>
	<entry>11</entry>
	<entry>search</entry>
	<entry>1.4</entry>
       </row>
       <row>
	<entry>Global Approx Limit</entry>
	<entry>12</entry>
	<entry>search</entry>
	<entry>2.0.8</entry>
       </row>
       <row>
	<entry>Maximum number of truncated terms (truncmax)</entry>
	<entry>13</entry>
	<entry>search</entry>
	<entry>2.0.10</entry>
       </row>
       <row>
	<entry>
	 Specifies whether un-indexed fields should be ignored.
	 A zero value (default) throws a diagnostic when an un-indexed
	 field is specified. A non-zero value makes it return 0 hits.
	</entry>
	<entry>14</entry>
	<entry>search</entry>
	<entry>2.0.16</entry>
       </row>
      </tbody>
     </tgroup>
    </table>

    <section id="querymodel-zebra-attr-sorting">
     <title>&zebra; Extension Embedded Sort Attribute (type 7)</title>
     <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>except</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 (&acro.apt;) node is separate from the
      rest and must be <literal>@or</literal>'ed.
      The term associated with &acro.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>
    </section>

    <!--
    &zebra; Extension Term Set Attribute
    From the manual text, I can not see what is the point with this feature.
    I think it makes more sense when there are multiple terms in a query, or
    something...

    We decided 2006-06-03 to disable this feature, as it is covered by
    scan within a resultset. Better use ressources to upgrade this
    feature for good performance.
    -->

    <!--
    <section id="querymodel-zebra-attr-estimation">
    <title>&zebra; Extension Term Set Attribute (type 8)</title>
    <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 &acro.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>
   </section>
    -->


    <section id="querymodel-zebra-attr-weight">
     <title>&zebra; Extension Rank Weight Attribute (type 9)</title>
     <para>
      Rank weight is a way to pass a value to a ranking algorithm - so
      that one &acro.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>
    </section>

    <section id="querymodel-zebra-attr-termref">
     <title>&zebra; Extension Term Reference Attribute (type 10)</title>
     <para>
      &zebra; supports the searchResult-1 facility.
      If the Term Reference Attribute (type 10) is
      given, that specifies a subqueryId value returned as part of the
      search result. It is a way for a client to name an &acro.apt; part of a
      query.
     </para>

     <warning>
      <para>
       Experimental. Do not use in production code.
      </para>
     </warning>

    </section>



    <section id="querymodel-zebra-local-attr-limit">
     <title>Local Approximative Limit Attribute (type 11)</title>
     <para>
      &zebra; computes - unless otherwise configured -
      the exact hit count for every &acro.apt;
      (leaf) in the query tree. These hit counts are returned as part of
      the searchResult-1 facility in the binary encoded &acro.z3950; search
      response packages.
     </para>
     <para>
      By setting an estimation limit size of the resultset of the &acro.apt;
      leaves, &zebra; stops processing the result set when the limit
      length is reached.
      Hit counts under this limit are still precise, but hit counts over it
      are estimated using the statistics gathered from the chopped
      result set.
     </para>
     <para>
      Specifying a limit of <literal>0</literal> results in exact hit counts.
     </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 11=1000 b
      </screen>
     </para>
     <note>
      <para>
       The estimated hit count facility makes searches faster, as one
       only needs to process large hit lists partially.
       It is mostly used in huge databases, where you you want trade
       exactness of hit counts against speed of execution.
      </para>
     </note>
     <warning>
      <para>
       Do not use approximative hit count limits
       in conjunction with relevance ranking, as re-sorting of the
       result set only works when the entire result set has
       been processed.
      </para>
     </warning>
    </section>

    <section id="querymodel-zebra-global-attr-limit">
     <title>Global Approximative Limit Attribute (type 12)</title>
     <para>
      By default &zebra; computes precise hit counts for a query as
      a whole. Setting attribute 12 makes it perform approximative
      hit counts instead. It has the same semantics as
      <literal>estimatehits</literal> for the <xref linkend="zebra-cfg"/>.
     </para>
     <para>
      The attribute (12) can occur anywhere in the query tree.
      Unlike regular attributes it does not relate to the leaf (&acro.apt;)
      - but to the whole query.
     </para>
     <warning>
      <para>
       Do not use approximative hit count limits
       in conjunction with relevance ranking, as re-sorting of the
       result set only works when the entire result set has
       been processed.
      </para>
     </warning>
    </section>

   </section>

   <section 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 scan operation query.
    </para>
    <table id="querymodel-zebra-attr-scan-table" frame="top">
     <title>&zebra; Scan Attribute Extensions</title>
     <tgroup cols="4">
      <thead>
       <row>
	<entry>Name</entry>
	<entry>Type</entry>
	<entry>Operation</entry>
	<entry>&zebra; version</entry>
       </row>
      </thead>
      <tbody>
       <row>
	<entry>Result Set Narrow</entry>
	<entry>8</entry>
	<entry>scan</entry>
	<entry>1.3</entry>
       </row>
       <row>
	<entry>Approximative Limit</entry>
	<entry>12</entry>
	<entry>scan</entry>
	<entry>2.0.20</entry>
       </row>
      </tbody>
     </tgroup>
    </table>

    <section id="querymodel-zebra-attr-narrow">
     <title>&zebra; Extension Result Set Narrow (type 8)</title>
     <para>
      If attribute Result Set Narrow (type 8)
      is given for scan, the value is the name of a
      result set. Each hit count in scan 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>

     <para>
      &zebra; 2.0.2 and later is able to skip 0 hit counts. This, however,
      is known not to scale if the number of terms to skip is high.
      This most likely will happen if the result set is small (and
      result in many 0 hits).
     </para>
    </section>

    <section id="querymodel-zebra-attr-approx">
     <title>&zebra; Extension Approximative Limit (type 12)</title>
     <para>
      The &zebra; Extension Approximative Limit (type 12) is a way to
      enable approximate hit counts for scan hit counts, in the same
      way as for search hit counts.
     </para>
    </section>
   </section>

   <section id="querymodel-idxpath">
    <title>&zebra; special &acro.idxpath; Attribute Set for &acro.grs1; indexing</title>
    <para>
     The attribute-set <literal>idxpath</literal> consists of a single
     Use (type 1) attribute. All non-use attributes behave as normal.
    </para>
    <para>
     This feature is enabled when defining the
     <literal>xpath enable</literal> option in the &acro.grs1; 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>
     <para>
      The <literal>idxpath</literal> is deprecated, may not be
      supported in future &zebra; versions, and should definitely
      not be used in production code.
     </para>
    </warning>

    <section id="querymodel-idxpath-use">
     <title>&acro.idxpath; Use Attributes (type = 1)</title>
     <para>
      This attribute set allows one to search &acro.grs1; filter indexed
      records by &acro.xpath; like structured index names.
     </para>

     <warning>
      <para>
       The <literal>idxpath</literal> option defines hard-coded
       index names, which might clash with your own index names.
      </para>
     </warning>

     <table id="querymodel-idxpath-use-table" frame="top">
      <title>&zebra; specific &acro.idxpath; Use Attributes (type 1)</title>
      <tgroup cols="4">
       <thead>
        <row>
         <entry>&acro.idxpath;</entry>
         <entry>Value</entry>
         <entry>String Index</entry>
         <entry>Notes</entry>
        </row>
       </thead>
       <tbody>
        <row>
         <entry>&acro.xpath; Begin</entry>
         <entry>1</entry>
         <entry>_XPATH_BEGIN</entry>
         <entry>deprecated</entry>
        </row>
        <row>
         <entry>&acro.xpath; End</entry>
         <entry>2</entry>
         <entry>_XPATH_END</entry>
         <entry>deprecated</entry>
        </row>
        <row>
         <entry>&acro.xpath; CData</entry>
         <entry>1016</entry>
         <entry>_XPATH_CDATA</entry>
         <entry>deprecated</entry>
        </row>
        <row>
         <entry>&acro.xpath; Attribute Name</entry>
         <entry>3</entry>
         <entry>_XPATH_ATTR_NAME</entry>
         <entry>deprecated</entry>
        </row>
        <row>
         <entry>&acro.xpath; Attribute CData</entry>
         <entry>1015</entry>
         <entry>_XPATH_ATTR_CDATA</entry>
         <entry>deprecated</entry>
        </row>
       </tbody>
      </tgroup>
     </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 &acro.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 &acro.xml; element node
      including an &acro.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>

    </section>
   </section>


   <section id="querymodel-pqf-apt-mapping">
    <title>Mapping from &acro.pqf; atomic &acro.apt; queries to &zebra; internal
     register indexes</title>
    <para>
     The rules for &acro.pqf; &acro.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>

    <section id="querymodel-pqf-apt-mapping-accesspoint">
     <title>Mapping of &acro.pqf; &acro.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;">&acro.z3950;</ulink>
      standard.
      All other access point types are &zebra; specific, and non-portable.
     </para>

     <table id="querymodel-zebra-mapping-accesspoint-types" frame="top">
      <title>Access point name mapping</title>
      <tgroup cols="4">
       <thead>
        <row>
         <entry>Access Point</entry>
         <entry>Type</entry>
         <entry>Grammar</entry>
         <entry>Notes</entry>
        </row>
       </thead>
       <tbody>
	<row>
	 <entry>Use attribute</entry>
	 <entry>numeric</entry>
	 <entry>[1-9][1-9]*</entry>
	 <entry>directly mapped to string index name</entry>
	</row>
	<row>
	 <entry>String index name</entry>
	 <entry>string</entry>
	 <entry>[a-zA-Z](\-?[a-zA-Z0-9])*</entry>
	 <entry>normalized name is used as internal string index name</entry>
	</row>
	<row>
	 <entry>&zebra; internal index name</entry>
	 <entry>zebra</entry>
	 <entry>_[a-zA-Z](_?[a-zA-Z0-9])*</entry>
	 <entry>hardwired internal string index name</entry>
	</row>
	<row>
	 <entry>&acro.xpath; special index</entry>
	 <entry>XPath</entry>
	 <entry>/.*</entry>
	 <entry>special xpath search for &acro.grs1; indexed records</entry>
	</row>
       </tbody>
      </tgroup>
     </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 &acro.bib1;, and may be
      omitted in the &acro.pqf; query.
     </para>

     <para>
      According to normalization and numeric
      use attribute mapping, it follows that the following
      &acro.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 bib1 @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
      &acro.bib1; Use Any (1016) is assumed.
      The predefined use attribute sets
      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>
      String indexes can be accessed directly,
      independently which attribute set is in use. These are just
      ignored. The above mentioned name normalization applies.
      String index names are defined in the
      used indexing  filter configuration files, for example in the
      &acro.grs1;
      <filename>*.abs</filename> configuration files, or in the
      <literal>alvis</literal> filter &acro.xslt; indexing stylesheets.
     </para>

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

     <para>
      Finally, &acro.xpath; access points are only
      available using the &acro.grs1; 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
      &acro.xpath; engine. See <xref linkend="querymodel-use-xpath"/>.

     </para>


    </section>


    <section id="querymodel-pqf-apt-mapping-structuretype">
     <title>Mapping of &acro.pqf; &acro.apt; structure and completeness to
      register type</title>
     <para>
      Internally &zebra; has in its 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="top">
      <title>Structure and completeness mapping to register types</title>
      <tgroup cols="4">
       <thead>
        <row>
         <entry>Structure</entry>
         <entry>Completeness</entry>
         <entry>Register type</entry>
         <entry>Notes</entry>
        </row>
       </thead>
       <tbody>
	<row>
	 <entry>
          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)
         </entry>
	 <entry>Incomplete field (@attr 6=1)</entry>
	 <entry>Word ('w')</entry>
	 <entry>Traditional tokenized and character normalized word index</entry>
	</row>
	<row>
	 <entry>
          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)
         </entry>
	 <entry>complete field' (@attr 6=3)</entry>
	 <entry>Phrase ('p')</entry>
	 <entry>Character normalized, but not tokenized index for phrase
          matches
         </entry>
	</row>
	<row>
	 <entry>urx (@attr 4=104)</entry>
	 <entry>ignored</entry>
	 <entry>URX/URL ('u')</entry>
	 <entry>Special index for URL web addresses</entry>
	</row>
	<row>
	 <entry>numeric (@attr 4=109)</entry>
	 <entry>ignored</entry>
	 <entry>Numeric ('n')</entry>
	 <entry>Special index for digital numbers</entry>
	</row>
	<row>
	 <entry>key (@attr 4=3)</entry>
	 <entry>ignored</entry>
	 <entry>Null bitmap ('0')</entry>
	 <entry>Used for non-tokenized and non-normalized bit sequences</entry>
	</row>
	<row>
	 <entry>year (@attr 4=4)</entry>
	 <entry>ignored</entry>
	 <entry>Year ('y')</entry>
	 <entry>Non-tokenized and non-normalized 4 digit numbers</entry>
	</row>
	<row>
	 <entry>date (@attr 4=5)</entry>
	 <entry>ignored</entry>
	 <entry>Date ('d')</entry>
	 <entry>Non-tokenized and non-normalized ISO date strings</entry>
	</row>
	<row>
	 <entry>ignored</entry>
	 <entry>ignored</entry>
	 <entry>Sort ('s')</entry>
	 <entry>Used with special sort attribute set (@attr 7=1, @attr 7=2)</entry>
	</row>
	<row>
	 <entry>overruled</entry>
	 <entry>overruled</entry>
	 <entry>special</entry>
	 <entry>Internal record ID register, used whenever
	  Relation Always Matches (@attr 2=103) is specified</entry>
	</row>
       </tbody>
      </tgroup>
     </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
      &acro.grs1; <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 &acro.grs1; <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
      &acro.grs1; <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 &acro.grs1;
      <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>

    </section>
   </section>

   <section  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="top">
     <title>Regular Expression Operands</title>
     <tgroup cols="2">
      <tbody>
       <row>
	<entry><literal>x</literal></entry>
	<entry>Matches the character <literal>x</literal>.</entry>
       </row>
       <row>
	<entry><literal>.</literal></entry>
	<entry>Matches any character.</entry>
       </row>
       <row>
	<entry><literal>[ .. ]</literal></entry>
	<entry>Matches the set of characters specified;
         such as <literal>[abc]</literal> or <literal>[a-c]</literal>.</entry>
       </row>
      </tbody>
     </tgroup>
    </table>

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

    <table id="querymodel-regular-operators-table" frame="top">
     <title>Regular Expression Operators</title>
     <tgroup cols="2">
      <tbody>
       <row>
	<entry><literal>x*</literal></entry>
	<entry>Matches <literal>x</literal> zero or more times.
	 Priority: high.</entry>
       </row>
       <row>
	<entry><literal>x+</literal></entry>
	<entry>Matches <literal>x</literal> one or more times.
	 Priority: high.</entry>
       </row>
       <row>
	<entry><literal>x?</literal></entry>
	<entry> Matches <literal>x</literal> zero or once.
	 Priority: high.</entry>
       </row>
       <row>
	<entry><literal>xy</literal></entry>
	<entry> Matches <literal>x</literal>, then <literal>y</literal>.
         Priority: medium.</entry>
       </row>
       <row>
	<entry><literal>x|y</literal></entry>
	<entry> Matches either <literal>x</literal> or <literal>y</literal>.
         Priority: low.</entry>
       </row>
       <row>
	<entry><literal>( )</literal></entry>
	<entry>The order of evaluation may be changed by using parentheses.</entry>
       </row>
      </tbody>
     </tgroup>
    </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>
   </section>


   <!--
   <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>
   -->
  </section>


  <section id="querymodel-cql-to-pqf">
   <title>Server Side &acro.cql; to &acro.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 &acro.cql;-to-&acro.pqf;
    converter, specifying the interpretation of various
    <ulink url="&url.cql;">&acro.cql;</ulink>
    indexes, relations, etc. in terms of Type-1 query attributes.
    <!-- The  yaz-client config file -->
   </para>
   <para>
    For example, using server-side &acro.cql;-to-&acro.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 &acro.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 &acro.cql;-to-&acro.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 <ulink url="&url.yaz.cql2pqf;">&acro.cql; to &acro.rpn; conversion</ulink>
    in the &yaz; manual.
   </para>
   <!--
   <para>
   See
   <ulink url="http://www.loc.gov/z3950/agency/zing/cql/dc-indexes.html"/>
   for the Maintenance Agency's work-in-progress mapping of Dublin Core
   indexes to Attribute Architecture (util, XD and BIB-2)
   attributes.
  </para>
   -->
  </section>

 </chapter>

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