<chapter id="server">
- <!-- $Id: server.xml,v 1.1 2002-04-09 13:26:26 adam Exp $ -->
+ <!-- $Id: server.xml,v 1.24 2006-06-13 13:45:08 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 ...]
+ zebrasrv [options] [listener-address ...]
</screen>
</para>
<term>-z</term>
<listitem>
<para>
- Use the Z39.50 protocol (default). These two options complement
- eachother. You can use both multiple times on the same command
- line, between listener-specifications (see below). This way, you
- can set up the server to listen for connections in both protocols
- concurrently, on different local ports.
+ Use the Z39.50 protocol. Currently the only protocol supported.
+ The option is retained for historical reasons, and for future
+ extensions.
</para>
</listitem>
</varlistentry>
<listitem>
<para>
The log level. Use a comma-separated list of members of the set
- {fatal,debug,warn,log,all,none}.
+ {fatal,debug,warn,log,all,none}.
</para>
</listitem>
</varlistentry>
<listitem>
<para>
Set the (approximate) maximum size of
- present response messages. Default is 1024 Kb (1 Mb).
+ present response messages. Default is 1024 KB (1 MB).
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
-
- <para>
- A <replaceable>listener-address</replaceable> consists of a transport
- mode followed by a colon (:) followed by a listener address.
- The transport mode is either <literal>ssl</literal> or
- <literal>tcp</literal>.
- </para>
-
- <para>
- For TCP, an address has the form
- </para>
-
- <para>
-
- <screen>
- hostname | IP-number [: portnumber]
- </screen>
-
- </para>
-
- <para>
- The port number defaults to 210 (standard Z39.50 port).
- </para>
-
- <para>
- Examples
- </para>
-
- <para>
-
- <screen>
- tcp:dranet.dra.com
-
- ssl:secure.lib.com:3000
- </screen>
-
- </para>
-
- <para>
- In both cases, the special hostname "@" is mapped to
- the address INADDR_ANY, which causes the server to listen on any local
- interface. To start the server listening on the registered port for
- Z39.50, and to drop root privileges once the ports are bound, execute
- the server like this (from a root shell):
- </para>
-
- <para>
-
- <screen>
- zebrasrv -u daemon tcp:@
- </screen>
-
- </para>
-
- <para>
- You can replace <literal>daemon</literal> with another user, eg.
- your own account, or a dedicated IR server account.
- </para>
-
- <para>
- The default behavior for <literal>zebrasrv</literal> is to establish
- a single TCP/IP listener, for the Z39.50 protocol, on port 9999.
- </para>
-
+ -->
</sect1>
+
<sect1 id="protocol-support">
<title>Z39.50 Protocol Support and Behavior</title>
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
- 1Mb by default.
+ 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"
</para>
<para>
- The server has full support for piggy-backed present requests (see
+ 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.
- </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 #</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> once or twice. 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>
+
<sect2>
<title>Present</title>
<para>
<title>Sort</title>
<para>
- Z39.50 specifies three diffent types of sort criterias.
+ 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
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>.
+ 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>
+ </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
+ &operation=searchRetrieve
+ &x-pquery=mineral
+ &startRecord=1
+ &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 frontendConfigFile</literal>
+ option rather than the
+ <literal>-c 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><config></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><cql2rpn></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
+ &operation=searchRetrieve
+ &query=title=utah and description=epicent*
+ &startRecord=1
+ &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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