correcting typo's

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

<chapter id="server">
 <!-- $Id: server.xml,v 1.22 2006-06-07 13:17:48 marc Exp $ -->
 <title>The Z39.50 Server</title>
 
 <sect1 id="zebrasrv">
  <title>Running the Z39.50 Server (zebrasrv)</title>

  <!--
   FIXME - We need to be consistent here, zebraidx had the options at the
           end, and lots of explaining text before them. Same for zebrasvr! -H
   FIXME - At least we need a small intro, what is zebrasvr, and how it
           can be run (inetd, nt service, stand-alone program, daemon...) -H
  -->

  <!-- re-write by MC, using the newly created input files for the 
   zebrasrv manpage -->


 <sect2><title>Description</title>
    <para>Zebra is a high-performance, general-purpose structured text indexing
   and retrieval engine. It reads structured records in a variety of input
   formats (eg. email, XML, MARC) and allows access to them through exact
   boolean search expressions and relevance-ranked free-text queries. 
   </para>
   <para>
    <command>zebrasrv</command> is the Z39.50 and  <ulink url="http://www.loc.gov/standards/sru/srw/">SRW</ulink>/U frontend
    server for the <command>Zebra</command> indexer.
   </para> 
   <para> 
    On Unix you can run the <command>zebrasrv</command>
    server from the command line - and put it
    in the background. It may also operate under the inet daemon.
    On WIN32 you can run the server as a console application or
    as a WIN32 Service.
   </para>
  </sect2>

 <sect2>
   <title>Synopsis</title>
    &zebrasrv-synopsis;
 </sect2>

 <sect2>
   <title>Options</title>
    
   <para>
    The options for <command>zebrasrv</command> are the same
    as those for YAZ' <command>yaz-ztest</command>.
    Option <literal>-c</literal> specifies a Zebra configuration
    file - if omitted <filename>zebra.cfg</filename> is read.
   </para>
   
  &zebrasrv-options;
  </sect2>

  <sect2><title>Files</title>
   <para>
    <filename>zebra.cfg</filename>
   </para>
  </sect2>
  <sect2><title>See Also</title>
   <para>
    <citerefentry>
     <refentrytitle>zebraidx</refentrytitle>
     <manvolnum>1</manvolnum>
    </citerefentry>,
    <citerefentry>
     <refentrytitle>yaz-ztest</refentrytitle>
     <manvolnum>8</manvolnum>
    </citerefentry>
   </para>
   <para>
    The Zebra software is Copyright <command>Index Data</command> 
    <filename>http://www.indexdata.dk</filename>
    and distributed under the
    GPLv2 license.
   </para> 
  </sect2>

  <!--
  <para>
   <emphasis remap="bf">Syntax</emphasis>

   <screen>
    zebrasrv [options] [listener-address ...]
   </screen>

  </para>

  <para>
   <emphasis remap="bf">Options</emphasis>
   <variablelist>

    <varlistentry>
     <term>-a <replaceable>APDU file</replaceable></term>
     <listitem>
      <para>
       Specify a file for dumping PDUs (for diagnostic purposes).
       The special name "-" sends output to <literal>stderr</literal>.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term>-c <replaceable>config-file</replaceable></term>
     <listitem>
      <para>
       Read configuration information from
       <replaceable>config-file</replaceable>.
       The default configuration is <literal>./zebra.cfg</literal>.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term>-S</term>
     <listitem>
      <para>
       Don't fork on connection requests. This can be useful for
       symbolic-level debugging. The server can only accept a single
       connection in this mode.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term>-z</term>
     <listitem>
      <para>
       Use the Z39.50 protocol. Currently the only protocol supported.
       The option is retained for historical reasons, and for future
       extensions.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term>-l <replaceable>logfile</replaceable></term>
     <listitem>
      <para>
       Specify an output file for the diagnostic messages.
       The default is to write this information to <literal>stderr</literal>.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term>-v <replaceable>log-level</replaceable></term>
     <listitem>
      <para>
       The log level. Use a comma-separated list of members of the set
       {fatal,debug,warn,log,all,none}.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term>-u <replaceable>username</replaceable></term>
     <listitem>
      <para>
       Set user ID. Sets the real UID of the server process to that of the
       given <replaceable>username</replaceable>.
       It's useful if you aren't comfortable with having the
       server run as root, but you need to start it as such to bind a
       privileged port.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term>-w <replaceable>working-directory</replaceable></term>
     <listitem>
      <para>
       Change working directory.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term>-i</term>
     <listitem>
      <para>
       Run under the Internet superserver, <literal>inetd</literal>.
       Make sure you use the logfile option <literal>-l</literal> in
       conjunction with this mode and specify the <literal>-l</literal>
       option before any other options.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term>-t <replaceable>timeout</replaceable></term>
     <listitem>
      <para>
       Set the idle session timeout (default 60 minutes).
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term>-k <replaceable>kilobytes</replaceable></term>
     <listitem>
      <para>
       Set the (approximate) maximum size of
       present response messages. Default is 1024 KB (1 MB).
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
  -->
 </sect1>


 <sect1 id="protocol-support">
  <title>Z39.50 Protocol Support and Behavior</title>

  <sect2>
   <title>Initialization</title>

   <para>
    During initialization, the server will negotiate to version 3 of the
    Z39.50 protocol, and the option bits for Search, Present, Scan,
    NamedResultSets, and concurrentOperations will be set, if requested by
    the client. The maximum PDU size is negotiated down to a maximum of
    1 MB by default.
   </para>

  </sect2>

  <sect2 id="search">
   <title>Search</title>

   <!--
    FIXME - Need to explain the string tag stuff before people get bogged 
            down with all these attribute numbers. Perhaps in its own
            chapter? -H
   -->

   <para>
    The supported query type are 1 and 101. All operators are currently
    supported with the restriction that only proximity units of type "word"
    are supported for the proximity operator.
    Queries can be arbitrarily complex.
    Named result sets are supported, and result sets can be used as operands
    without limitations.
    Searches may span multiple databases.
   </para>

   <para>
    The server has full support for piggy-backed retrieval (see
    also the following section).
   </para>

   <para>
    <emphasis>Use</emphasis> attributes 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 Bib-1 Any is assumed.
   </para>

   <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
    <literal>.abs</literal> file that contains a
    <literal>p</literal>-specifier.
    <!-- ### whatever the hell _that_ is -->
   </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 <literal>.abs</literal> file.
   </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
    <literal>.abs</literal> 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 <literal>.abs</literal> 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 <literal>.abs</literal> 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>
    <title>Regular expressions</title>
    
    <para>
     Each term in a query is interpreted as a regular expression if
     the truncation value is either <emphasis>Regxp-1</emphasis> (102)
     or <emphasis>Regxp-2</emphasis> (103).
     Both query types follow the same syntax with the operands:
     <variablelist>

      <varlistentry>
       <term>x</term>
       <listitem>
        <para>
         Matches the character <emphasis>x</emphasis>.
        </para>
       </listitem>
      </varlistentry>
      <varlistentry>
       <term>.</term>
       <listitem>
        <para>
         Matches any character.
        </para>
       </listitem>
      </varlistentry>
      <varlistentry>
       <term><literal>[</literal>..<literal>]</literal></term>
       <listitem>
        <para>
         Matches the set of characters specified;
         such as <literal>[abc]</literal> or <literal>[a-c]</literal>.
        </para>
       </listitem>
      </varlistentry>
     </variablelist>
     and the operators:
     <variablelist>
      
      <varlistentry>
       <term>x*</term>
       <listitem>
        <para>
         Matches <emphasis>x</emphasis> zero or more times. Priority: high.
        </para>
       </listitem>
      </varlistentry>
      <varlistentry>
       <term>x+</term>
       <listitem>
        <para>
         Matches <emphasis>x</emphasis> one or more times. Priority: high.
        </para>
       </listitem>
      </varlistentry>
      <varlistentry>
       <term>x?</term>
       <listitem>
        <para>
         Matches <emphasis>x</emphasis> zero or once. Priority: high.
        </para>
       </listitem>
      </varlistentry>
      <varlistentry>
       <term>xy</term>
       <listitem>
        <para>
         Matches <emphasis>x</emphasis>, then <emphasis>y</emphasis>.
         Priority: medium.
        </para>
       </listitem>
      </varlistentry>
      <varlistentry>
       <term>x|y</term>
       <listitem>
        <para>
         Matches either <emphasis>x</emphasis> or <emphasis>y</emphasis>.
         Priority: low.
        </para>
       </listitem>
      </varlistentry>
     </variablelist>
     The order of evaluation may be changed by using parentheses.
    </para>

    <para>
     If the first character of the <emphasis>Regxp-2</emphasis> 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. 
    </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>

   </sect3>

   <sect3>
    <title>Query examples</title>

    <para>
     Phrase search for <emphasis>information retrieval</emphasis> in
     the title-register:
     <screen>
      @attr 1=4 "information retrieval"
     </screen>
    </para>

    <para>
     Ranked search for the same thing:
     <screen>
      @attr 1=4 @attr 2=102 "Information retrieval"
     </screen>
    </para>

    <para>
     Phrase search with a regular expression:
     <screen>
      @attr 1=4 @attr 5=102 "informat.* retrieval"
     </screen>
    </para>

    <para>
     Ranked search with a regular expression:
     <screen>
      @attr 1=4 @attr 5=102 @attr 2=102 "informat.* retrieval"
     </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>
      @attr 4=109 @attr 2=5 @attr gils 1=2038 -114
     </screen> 
    </para>
   </sect3>
   </sect2>
   
  <sect2>
   <title>Present</title>
   <para>
    The present facility is supported in a standard fashion. The requested
    record syntax is matched against the ones supported by the profile of
    each record retrieved. If no record syntax is given, SUTRS is the
    default. The requested element set name, again, is matched against any
    provided by the relevant record profiles.
   </para>
  </sect2>
  <sect2>
   <title>Scan</title>
   <para>
    The attribute combinations provided with the termListAndStartPoint are
    processed in the same way as operands in a query (see above).
    Currently, only the term and the globalOccurrences are returned with
    the termInfo structure.
   </para>
  </sect2>
  <sect2>
   <title>Sort</title>

   <para>
    Z39.50 specifies three different types of sort criteria.
    Of these Zebra supports the attribute specification type in which
    case the use attribute specifies the "Sort register".
    Sort registers are created for those fields that are of type "sort" in
    the default.idx file. 
    The corresponding character mapping file in default.idx specifies the
    ordinal of each character used in the actual sort.
   </para>

   <para>
    Z39.50 allows the client to specify sorting on one or more input
    result sets and one output result set.
    Zebra supports sorting on one result set only which may or may not
    be the same as the output result set.
   </para>
  </sect2>
  <sect2>
   <title>Close</title>
   <para>
    If a Close PDU is received, the server will respond with a Close PDU
    with reason=FINISHED, no matter which protocol version was negotiated
    during initialization. If the protocol version is 3 or more, the
    server will generate a Close PDU under certain circumstances,
    including a session timeout (60 minutes by default), and certain kinds of
    protocol errors. Once a Close PDU has been sent, the protocol
    association is considered broken, and the transport connection will be
    closed immediately upon receipt of further data, or following a short
    timeout.
   </para>
  </sect2>
   
   <sect2>
    <title>Explain</title>
    <para>
     Zebra maintains a "classic" 
     <ulink url="&url.z39.50.explain;">Explain</ulink> database
     on the side. 
     This database is called <literal>IR-Explain-1</literal> and can be
     searched using the attribute set <literal>exp-1</literal>.
    </para>
    <para>
     The records in the explain database are of type 
     <literal>grs.sgml</literal> and can be retrieved as
     <literal>SUTRS</literal>, <literal>XML</literal>, 
     <literal>GRS-1</literal> and  <literal>ASN.1</literal> Explain.
    </para>
    <para>
     Classic Explain only defines retrieaval of Explain information
     via ASN.1. Pratically no Z39.50 clients supports this. Fortunately
     they don't have to - since Zebra allows retrieval of this information
     in the other formats.
    </para>
    <para>
     The root element for the Explain grs.sgml records is 
     <literal>explain</literal>, thus 
     <filename>explain.abs</filename> is used for indexing.
    </para>
    <note>
     <para>
      Zebra <emphasis>must</emphasis> be able to locate
      <filename>explain.abs</filename> in order to index the Explain
      records properly. Zebra will work without it but the information
      will not be searchable.
     </para>
    </note>
    <para>
     The following Explain categories are supported: 
     <literal>CategoryList</literal>, <literal>TargetInfo</literal>,
     <literal>DatabaseInfo</literal>, <literal>AttributeDetails</literal>.
    </para>
    <para>
     The following Explain search atributes are supported:
     <literal>ExplainCategory</literal> (@attr 1=1), 
     <literal>DatabaseName</literal> (@attr 1=3), 
     <literal>DateAdded</literal> (@attr 1=9), 
     <literal>DateChanged</literal>(@ayyt 1=10).
     See <filename>tab/explain.att</filename> for more information.
    </para>
    
    <sect3>
     <title>Example searches with yaz-client</title>

     
     <para>
      List supported categories to find out which explain commands are
      supported: 
      <screen>
       Z> base IR-Explain-1
       Z> @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> @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> f @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> @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> @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> @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> @attrset exp1 @and @attr 1=1 attributedetails @attr 1=3 Default
      </screen>
     </para>

    </sect3>
   </sect2>
 </sect1>
</chapter>


<chapter id="server-sru">
 <title>The SRU/SRW Server</title>
 <para>
  In addition to Z39.50, Zebra supports the more recent and
  web-friendly IR protocol SRU, described at
  <ulink url="http://www.loc.gov/sru"/>.
  SRU is ``Search/Retrieve via URL'', a simple, REST-like protocol
  that uses HTTP GET to request search responses.  The request
  itself is made of parameters such as
  <literal>query</literal>,
  <literal>startRecord</literal>,
  <literal>maximumRecords</literal>
  and
  <literal>recordSchema</literal>;
  the response is an XML document containing hit-count, result-set
  records, diagnostics, etc.  SRU can be thought of as a re-casting
  of Z39.50 semantics in web-friendly terms; or as a standardisation
  of the ad-hoc query parameters used by search engines such as Google
  and AltaVista; or as a superset of A9's OpenSearch (which it
  predates).
 </para>
 <para>
  Zebra further supports SRW, described at
  <ulink url="http://www.loc.gov/srw"/>.
  SRW is the ``Search/Retrieve Web Service'', a SOAP-based alternative
  implementation of the abstract protocol that SRU implements as HTTP
  GET requests.  In SRW, requests are encoded as XML documents which
  are posted to the server.  The responses are identical to those
  returned by SRU servers, except that they are wrapped in a several
  layers of SOAP envelope.
 </para>
 <para>
  Zebra supports all three protocols - Z39.50, SRU and SRW - on the
  same port, recognising what protocol is used by each incoming
  requests and handling them accordingly.  This is a achieved through
  the use of Deep Magic; civilians are warned not to stand too close.
 </para>
 <para>
  From here on, ``SRU'' is used to indicate both the SRU and SRW
  protocols, as they are identical except for the transport used for
  the protocol packets and Zebra's support for them is equivalent.
 </para>

 <sect1 id="server-sru-run">
  <title>Running the SRU Server (zebrasrv)</title>
  <para>
   Because Zebra supports all three protocols on one port, it would
   seem to follow that the SRU server is run in the same way as
   the Z39.50 server, as described above.  This is true, but only in
   an uninterestingly vacuous way: a Zebra server run in this manner
   will indeed recognise and accept SRU requests; but since it
   doesn't know how to handle the CQL queries that these protocols
   use, all it can do is send failure responses.
  </para>
  <note>
   <para>
    It is possible to cheat, by having SRU search Zebra with
    a PQF query instead of CQL, using the
    <literal>x-pquery</literal>
    parameter instead of
    <literal>query</literal>.
    This is a
    <emphasis role="strong">non-standard extension</emphasis>
    of CQL, and a
    <emphasis role="strong">very naughty</emphasis>
    thing to do, but it does give you a way to see Zebra serving SRU
    ``right out of the box''.  If you start your favourite Zebra
    server in the usual way, on port 9999, then you can send your web
    browser to:
  </para>
  <screen>
        http://localhost:9999/Default?version=1.1
                &amp;operation=searchRetrieve
                &amp;x-pquery=mineral
                &amp;startRecord=1
                &amp;maximumRecords=1
  </screen>
  <para>
    This will display the XML-formatted SRU response that includes the
    first record in the result-set found by the query
    <literal>mineral</literal>.  (For clarity, the SRU URL is shown
    here broken across lines, but the lines should be joined to gether
    to make single-line URL for the browser to submit.)
   </para>
  </note>
  <para>
   In order to turn on Zebra's support for CQL queries, it's necessary
   to have the YAZ generic front-end (which Zebra uses) translate them
   into the Z39.50 Type-1 query format that is used internally.  And
   to do this, the generic front-end's own configuration file must be
   used.  This file is described
   <link linkend="gfs-config">elsewhere</link>;
   the salient point for SRU support is that
   <command>zebrasrv</command>
   must be started with the
   <literal>-f&nbsp;frontendConfigFile</literal>
   option rather than the
   <literal>-c&nbsp;zebraConfigFile</literal>
   option,
   and that the front-end configuration file must include both a
   reference to the Zebra configuration file and the CQL-to-PQF
   translator configuration file.
  </para>
  <para>
   A minimal front-end configuration file that does this would read as
   follows:
  </para>
  <screen><![CDATA[
        <yazgfs>
          <server>
            <config>zebra.cfg</config>
            <cql2rpn>../../tab/pqf.properties</cql2rpn>
          </server>
        </yazgfs>
]]></screen>
  <para>
   The
   <literal>&lt;config&gt;</literal>
   element contains the name of the Zebra configuration file that was
   previously specified by the
   <literal>-c</literal>
   command-line argument, and the
   <literal>&lt;cql2rpn&gt;</literal>
   element contains the name of the CQL properties file specifying how
   various CQL indexes, relations, etc. are translated into Type-1
   queries.
  </para>
  <para>
   A zebra server running with such a configuration can then be
   queried using proper, conformant SRU URLs with CQL queries:
  </para>
  <screen>
        http://localhost:9999/Default?version=1.1
                &amp;operation=searchRetrieve
                &amp;query=title=utah and description=epicent*
                &amp;startRecord=1
                &amp;maximumRecords=1
  </screen>
 </sect1>

 <sect1 id="server-sru-support">
  <title>SRU and SRW Protocol Support and Behavior</title>
  <para>
   Zebra running as an SRU server supports SRU version 1.1, including
   CQL version 1.1.  In particular, it provides support for the
   following elements of the protocol.
  </para>

  <sect2>
   <title>Search and Retrieval</title>
   <para>
    Zebra fully supports SRU's core
    <literal>searchRetrieve</literal>
    operation, as described at
    <ulink url="http://www.loc.gov/standards/sru/sru-spec.html"/>
   </para>
   <para>
    One of the great strengths of SRU is that it mandates a standard
    query language, CQL, and that all conforming implementations can
    therefore be trusted to correctly interpret the same queries.  It
    is with some shame, then, that we admit that Zebra also supports
    an additional query language, our own Prefix Query Format (PQF,
    <ulink url="http://indexdata.com/yaz/doc/tools.tkl#PQF"/>).
    A PQF query is submitted by using the extension parameter
    <literal>x-pquery</literal>,
    in which case the
    <literal>query</literal>
    parameter must be omitted, which makes the request not valid SRU.
    Please don't do this.
   </para>
  </sect2>

  <sect2>
   <title>Scan</title>
   <para>
    Zebra does <emphasis>not</emphasis> support SRU's
    <literal>scan</literal>
    operation, as described at
    <ulink url="http://www.loc.gov/standards/sru/scan/"/>
   </para>
   <para>
    This is a rather embarrassing surprise as the pieces are all
    there: Z39.50 scan is supported, and SRU scan requests are
    recognised and diagnosed.  To add further to the embarrassment, a
    mutant form of SRU scan <emphasis>is</emphasis> supported, using
    the non-standard <literal>x-pScanClause</literal> parameter in
    place of the standard <literal>scanClause</literal> to scan on a
    PQF query clause.
   </para>
  </sect2>

  <sect2>
   <title>Explain</title>
   <para>
    Zebra fully supports SRU's core
    <literal>explain</literal>
    operation, as described at
    <ulink url="http://www.loc.gov/standards/sru/explain/index.html"/>
   </para>
   <para>
    The ZeeRex record explaining a database may be requested either
    with a fully fledged SRU request (with
    <literal>operation</literal>=<literal>explain</literal>
    and version-number specified)
    or with a simple HTTP GET at the server's basename.
    The ZeeRex record returned in response is the one embedded
    in the YAZ Frontend Server configuration file that is described in the
    <link linkend="gfs-config">Virtual Hosts</link> documentation.
   </para>
    <para>
     Unfortunately, the data found in the 
     CQL-to-PQF text file must be added by hand-craft into the explain
     section of the YAZ Frontend Server configuration file to be able
     to provide a suitable explain record. 
     Too bad, but this is all extreme
     new alpha stuff, and a lot of work has yet to be done ..
    </para>
    <para>
     There is no linkeage whatsoever between the Z39.50 explain model
     and the SRU/SRW explain response (well, at least not implemented
     in Zebra, that is ..).  Zebra does not provide a means using
     Z39.50 to obtain the ZeeRex record.
     </para>
  </sect2>

  <sect2>
   <title>Some SRU Examples</title>
    <para>
     Surf into <literal>http://localhost:9999</literal>
     to get an explain response, or use
     <screen><![CDATA[
      http://localhost:9999/?version=1.1&operation=explain
     ]]></screen>
    </para>
    <para>
     See number of hits for a query
     <screen><![CDATA[
       http://localhost:9999/?version=1.1&operation=searchRetrieve
                       &query=text=(plant%20and%20soil)
     ]]></screen>
    </para>
    <para>
      Fetch record 5-7 in Dublin Core format
     <screen><![CDATA[
       http://localhost:9999/?version=1.1&operation=searchRetrieve
                       &query=text=(plant%20and%20soil)
                       &startRecord=5&maximumRecords=2&recordSchema=dc
     ]]></screen>
    </para>
    <para>
     Even search using PQF queries using the <emphasis>extended naughty 
     verb</emphasis> <literal>x-pquery</literal>
     <screen><![CDATA[
      http://localhost:9999/?version=1.1&operation=searchRetrieve
                       &x-pquery=@attr%201=text%20@and%20plant%20soil
     ]]></screen>
    </para>
    <para>
     Or scan indexes using the <emphasis>extended extremely naughty 
     verb</emphasis> <literal>x-pScanClause</literal>
     <screen><![CDATA[
      http://localhost:9999/?version=1.1&operation=scan
                       &x-pScanClause=@attr%201=text%20something
     ]]></screen>
     <emphasis>Don't do this in production code!</emphasis>
     But it's a great fast debugging aid.
    </para>
  </sect2>

  <sect2>
   <title>Initialization, Present, Sort, Close</title>
   <para>
    In the Z39.50 protocol, Initialization, Present, Sort and Close
    are separate operations.  In SRU, however, these operations do not
    exist.
   </para>
   <itemizedlist>
    <listitem>
     <para>
      SRU has no explicit initialization handshake phase, but
      commences immediately with searching, scanning and explain
      operations.
     </para>
    </listitem>
    <listitem>
     <para>
      Neither does SRU have a close operation, since the protocol is
      stateless and each request is self-contained.  (It is true that
      multiple SRU request/response pairs may be implemented as
      multiple HTTP request/response pairs over a single persistent
      TCP/IP connection; but the closure of that connection is not a
      protocol-level operation.)
     </para>
    </listitem>
    <listitem>
     <para>
      Retrieval in SRU is part of the
      <literal>searchRetrieve</literal> operation, in which a search
      is submitted and the response includes a subset of the records
      in the result set.  There is no direct analogue of Z39.50's
      Present operation which requests records from an established
      result set.  In SRU, this is achieved by sending a subsequent
      <literal>searchRetrieve</literal> request with the query
      <literal>cql.resultSetId=</literal><emphasis>id</emphasis> where 
      <emphasis>id</emphasis> is the identifier of the previously
      generated result-set.
     </para>
    </listitem>
    <listitem>
     <para>
      Sorting in CQL is done within the
      <literal>searchRetrieve</literal> operation - in v1.1, by an
      explicit <literal>sort</literal> parameter, but the forthcoming
      v1.2 or v2.0 will most likely use an extension of the query
      language, CQL for sorting: see
      <ulink url="http://zing.z3950.org/cql/sorting.html"/>
     </para>
    </listitem>
   </itemizedlist>
   <para>
    It can be seen, then, that while Zebra operating as an SRU server
    does not provide the same set of operations as when operating as a
    Z39.50 server, it does provide equivalent functionality.
   </para>
  </sect2>
 </sect1>
</chapter>

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