-<!-- $Id: book.xml,v 1.13 2006-04-22 13:28:05 adam Exp $ -->
+<?xml version="1.0" standalone="no"?>
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1//EN"
+ "http://www.oasis-open.org/docbook/xml/4.1/docbookx.dtd"
+[
+ <!ENTITY local SYSTEM "local.ent">
+ <!ENTITY manref SYSTEM "manref.xml">
+ <!ENTITY progref SYSTEM "progref.xml">
+ <!ENTITY % common SYSTEM "common/common.ent">
+ %common;
+ <!-- Next line allows imagedata/@format="PDF" and is taken from
+ http://lists.oasis-open.org/archives/docbook/200303/msg00163.html
+ -->
+ <!ENTITY % local.notation.class "| PDF">
+ <!-- Next line is necessary for some XML parsers, for reasons I
+ don't understand. I got this from
+ http://lists.oasis-open.org/archives/docbook/200303/msg00180.html
+ -->
+ <!NOTATION PDF SYSTEM "PDF">
+]>
+<!-- $Id: book.xml,v 1.38 2006-09-08 14:12:28 marc Exp $ -->
+<book id="metaproxy">
<bookinfo>
<title>Metaproxy - User's Guide and Reference</title>
<author>
- <firstname>Mike</firstname><surname>Taylor</surname>
+ <firstname>Adam</firstname><surname>Dickmeiss</surname>
</author>
<author>
- <firstname>Adam</firstname><surname>Dickmeiss</surname>
+ <firstname>Marc</firstname><surname>Cromme</surname>
+ </author>
+ <author>
+ <firstname>Mike</firstname><surname>Taylor</surname>
</author>
<copyright>
<year>2006</year>
Metaproxy is a universal router, proxy and encapsulated
metasearcher for information retrieval protocols. It accepts,
processes, interprets and redirects requests from IR clients using
- standard protocols such as ANSI/NISO Z39.50 (and in the future SRU
- and SRW), as well as functioning as a limited
- HTTP server. Metaproxy is configured by an XML file which
+ standard protocols such as
+ <ulink url="&url.z39.50;">ANSI/NISO Z39.50</ulink>
+ (and in the future <ulink url="&url.sru;">SRU</ulink>
+ and <ulink url="&url.srw;">SRW</ulink>), as
+ well as functioning as a limited
+ <ulink url="&url.http;">HTTP</ulink> server.
+ Metaproxy is configured by an XML file which
specifies how the software should function in terms of routes that
the request packets can take through the proxy, each step on a
route being an instantiation of a filter. Filters come in many
using the filter API.
</simpara>
<simpara>
- The terms under which Metaproxy will be distributed have yet to be
- established, but it will not necessarily be open source; so users
- should not at this stage redistribute the code without explicit
- written permission from the copyright holders, Index Data ApS.
+ Metaproxy is <emphasis>not</emphasis> open-source software, but
+ may be freely downloaded, unpacked, inspected, built and run for
+ evaluation purposes. Deployment requires a separate, commercial,
+ license.
+ </simpara>
+ <simpara>
+ <inlinemediaobject>
+ <imageobject>
+ <imagedata fileref="common/id.png" format="PNG"/>
+ </imageobject>
+ <imageobject>
+ <imagedata fileref="common/id.eps" format="EPS"/>
+ </imageobject>
+ </inlinemediaobject>
</simpara>
</abstract>
</bookinfo>
<title>Introduction</title>
+ <para>
+ <ulink url="&url.metaproxy;">Metaproxy</ulink>
+ is a standalone program that acts as a universal router, proxy and
+ encapsulated metasearcher for information retrieval protocols such
+ as <ulink url="&url.z39.50;">Z39.50</ulink>, and in the future
+ <ulink url="&url.sru;">SRU</ulink> and <ulink url="&url.srw;">SRW</ulink>.
+ To clients, it acts as a server of these protocols: it can be searched,
+ records can be retrieved from it, etc.
+ To servers, it acts as a client: it searches in them,
+ retrieves records from them, etc. it satisfies its clients'
+ requests by transforming them, multiplexing them, forwarding them
+ on to zero or more servers, merging the results, transforming
+ them, and delivering them back to the client. In addition, it
+ acts as a simple <ulink url="&url.http;">HTTP</ulink> server; support
+ for further protocols can be added in a modular fashion, through the
+ creation of new filters.
+ </para>
+ <screen>
+ Anything goes in!
+ Anything goes out!
+ Fish, bananas, cold pyjamas,
+ Mutton, beef and trout!
+ - attributed to Cole Porter.
+ </screen>
+ <para>
+ Metaproxy is a more capable alternative to
+ <ulink url="&url.yazproxy;">YAZ Proxy</ulink>,
+ being more powerful, flexible, configurable and extensible. Among
+ its many advantages over the older, more pedestrian work are
+ support for multiplexing (encapsulated metasearching), routing by
+ database name, authentication and authorisation and serving local
+ files via HTTP. Equally significant, its modular architecture
+ facilitites the creation of pluggable modules implementing further
+ functionality.
+ </para>
+ <para>
+ This manual will describe how to install Metaproxy
+ before giving an overview of its architecture, then discussing the
+ key concept of a filter in some depth and giving an overview of
+ the various filter types, then discussing the configuration file
+ format. After this come several optional chapters which may be
+ freely skipped: a detailed discussion of virtual databases and
+ multi-database searching, some notes on writing extensions
+ (additional filter types) and a high-level description of the
+ source code. Finally comes the reference guide, which contains
+ instructions for invoking the <command>metaproxy</command>
+ program, and detailed information on each type of filter,
+ including examples.
+ </para>
+ </chapter>
+
+ <chapter id="license">
+ <title>The Metaproxy License</title>
+ <orderedlist numeration="arabic">
+ <listitem>
+ <para>
+ You are allowed to download this software for evaluation purposes.
+ You can unpack it, build it, run it, see how it works and how it fits
+ your needs, all at zero cost.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ You may NOT deploy the software. For the purposes of this license,
+ deployment means running it for any purpose other than evaluation,
+ whether or not you or anyone else makes a profit from doing so. If
+ you wish to deploy the software, you must first contact Index Data and
+ arrange to purchase a DEPLOYMENT LICENCE. If you are unsure
+ whether or not your proposed use of the software constitutes
+ deployment, email us at <literal>info@indexdata.com</literal>
+ for clarification.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ You may modify your copy of the software (fix bugs, add features)
+ if you need to. We encourage you to send your changes back to us for
+ integration into the master copy, but you are not obliged to do so. You
+ may NOT pass your changes on to any other party.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ There is NO WARRANTY for this software, to the extent permitted by
+ applicable law. We provide the software ``as is'' without warranty of
+ any kind, either expressed or implied, including, but not limited to, the
+ implied warranties of MERCHANTABILITY and FITNESS FOR A
+ PARTICULAR PURPOSE. The entire risk as to the quality and
+ performance of the software is with you. Should the software prove
+ defective, you assume the cost of all necessary servicing, repair or
+ correction. In no event unless required by applicable law will we be
+ liable to you for damages, arising out of the use of the software,
+ including but not limited to loss of data or data being rendered
+ inaccurate.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ All rights to the software are reserved by Index Data except where
+ this license explicitly says otherwise.
+ </para>
+ </listitem>
+ </orderedlist>
+ </chapter>
+
+ <chapter id="installation">
+ <title>Installation</title>
+ <para>
+ Metaproxy depends on the following tools/libraries:
+ <variablelist>
+ <varlistentry><term><ulink url="&url.yazplusplus;">YAZ++</ulink></term>
+ <listitem>
+ <para>
+ This is a C++ library based on <ulink url="&url.yaz;">YAZ</ulink>.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry><term><ulink url="&url.libxslt;">Libxslt</ulink></term>
+ <listitem>
+ <para>This is an XSLT processor - based on
+ <ulink url="&url.libxml2;">Libxml2</ulink>. Both Libxml2 and
+ Libxslt must be installed with the development components
+ (header files, etc.) as well as the run-time libraries.
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry><term><ulink url="&url.boost;">Boost</ulink></term>
+ <listitem>
+ <para>
+ The popular C++ library. Initial versions of Metaproxy
+ was built with 1.33.0. Version 1.33.1 works too.
+ </para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </para>
+ <para>
+ In order to compile Metaproxy a modern C++ compiler is
+ required. Boost, in particular, requires the C++ compiler
+ to facilitate the newest features. Refer to Boost
+ <ulink url="&url.boost.compilers.status;">Compiler Status</ulink>
+ for more information.
+ </para>
+ <para>
+ We have succesfully built Metaproxy using the compilers
+ <ulink url="&url.gcc;">GCC</ulink> version 4.0 and
+ <ulink url="&url.vstudio;">Microsoft Visual Studio</ulink> 2003/2005.
+ </para>
+
+ <section id="installation.unix">
+ <title>Installation on Unix (from Source)</title>
<para>
- <ulink url="http://www.indexdata.com/metaproxy/">Metaproxy</ulink>
- is a standalone program that acts as a universal router, proxy and
- encapsulated metasearcher for information retrieval protocols such
- as Z39.50, and in the future SRU and SRW. To clients, it acts as a
- server of these
- protocols: it can be searched, records can be retrieved from it,
- etc. To servers, it acts as a client: it searches in them,
- retrieves records from them, etc. it satisfies its clients'
- requests by transforming them, multiplexing them, forwarding them
- on to zero or more servers, merging the results, transforming
- them, and delivering them back to the client. In addition, it
- acts as a simple HTTP server; support for further protocols can be
- added in a modular fashion, through the creation of new filters.
+ Here is a quick step-by-step guide on how to compile all the
+ tools that Metaproxy uses. Only few systems have none of the required
+ tools binary packages. If, for example, Libxml2/libxslt are already
+ installed as development packages use those (and omit compilation).
+ </para>
+
+ <para>
+ Libxml2/libxslt:
</para>
<screen>
- Anything goes in!
- Anything goes out!
- Cold bananas, fish, pyjamas,
- Mutton, beef and trout!
- - attributed to Cole Porter.
+ gunzip -c libxml2-version.tar.gz|tar xf -
+ cd libxml2-version
+ ./configure
+ make
+ su
+ make install
+ </screen>
+ <screen>
+ gunzip -c libxslt-version.tar.gz|tar xf -
+ cd libxslt-version
+ ./configure
+ make
+ su
+ make install
</screen>
<para>
- Metaproxy is a more capable alternative to
- <ulink url="http://www.indexdata.com/yazproxy/">YAZ Proxy</ulink>,
- being more powerful, flexible, configurable and extensible. Among
- its many advantages over the older, more pedestrian work are
- support for multiplexing (encapsulated metasearching), routing by
- database name, authentication and authorisation and serving local
- files via HTTP. Equally significant, its modular architecture
- facilitites the creation of pluggable modules implementing further
- functionality.
+ YAZ/YAZ++:
</para>
+ <screen>
+ gunzip -c yaz-version.tar.gz|tar xf -
+ cd yaz-version
+ ./configure
+ make
+ su
+ make install
+ </screen>
+ <screen>
+ gunzip -c yazpp-version.tar.gz|tar xf -
+ cd yazpp-version
+ ./configure
+ make
+ su
+ make install
+ </screen>
<para>
- This manual will briefly describe Metaproxy's licensing situation
- before giving an overview of its architecture, then discussing the
- key concept of a filter in some depth and giving an overview of
- the various filter types, then discussing the configuration file
- format. After this come several optional chapters which may be
- freely skipped: a detailed discussion of virtual databases and
- multi-database searching, some notes on writing extensions
- (additional filter types) and a high-level description of the
- source code. Finally comes the reference guide, which contains
- instructions for invoking the <command>metaproxy</command>
- program, and detailed information on each type of filter,
- including examples.
+ Boost:
</para>
- </chapter>
+ <screen>
+ gunzip -c boost-version.tar.gz|tar xf -
+ cd boost-version
+ ./configure
+ make
+ su
+ make install
+ </screen>
+ <para>
+ Metaproxy:
+ </para>
+ <screen>
+ gunzip -c metaproxy-version.tar.gz|tar xf -
+ cd metaproxy-version
+ ./configure
+ make
+ su
+ make install
+ </screen>
+ </section>
+ <section id="installation.debian">
+ <title>Installation on Debian GNU/Linux</title>
+ <para>
+ All dependencies for Metaproxy are available as
+ <ulink url="&url.debian;">Debian</ulink>
+ packages for the sarge (stable in 2005) and etch (testing in 2005)
+ distributions.
+ </para>
+ <para>
+ The procedures for Debian based systems, such as
+ <ulink url="&url.ubuntu;">Ubuntu</ulink> is probably similar
+ </para>
+ <para>
+ There is currently no official Debian package for YAZ++.
+ And the Debian package for YAZ is probably too old.
+ Update the <filename>/etc/apt/sources.list</filename>
+ to include the Index Data repository.
+ See YAZ' <ulink url="&url.yaz.download.debian;">Download Debian</ulink>
+ for more information.
+ </para>
+ <screen>
+ apt-get install libxslt1-dev
+ apt-get install libyazpp-dev
+ apt-get install libboost-dev
+ apt-get install libboost-thread-dev
+ apt-get install libboost-date-time-dev
+ apt-get install libboost-program-options-dev
+ apt-get install libboost-test-dev
+ </screen>
+ <para>
+ With these packages installed, the usual configure + make
+ procedure can be used for Metaproxy as outlined in
+ <xref linkend="installation.unix"/>.
+ </para>
+ </section>
+ <section id="installation.windows">
+ <title>Installation on Windows</title>
+ <para>
+ Metaproxy can be compiled with Microsoft
+ <ulink url="&url.vstudio;">Visual Studio</ulink>.
+ Version 2003 (C 7.1) and 2005 (C 8.0) is known to work.
+ </para>
+ <section id="installation.windows.boost">
+ <title>Boost</title>
+ <para>
+ Get Boost from its <ulink url="&url.boost;">home page</ulink>.
+ You also need Boost Jam (an alternative to make).
+ That's also available from the Boost home page.
+ The files to be downloaded are called something like:
+ <filename>boost_1_33-1.exe</filename>
+ and
+ <filename>boost-jam-3.1.12-1-ntx86.zip</filename>.
+ Unpack Boost Jam first. Put <filename>bjam.exe</filename>
+ in your system path. Make a command prompt and ensure
+ it can be found automatically. If not check the PATH.
+ The Boost .exe is a self-extracting exe with
+ complete source for Boost. Compile that source with
+ Boost Jam (An alternative to Make).
+ The compilation takes a while.
+ For Visual Studio 2003, use
+ <screen>
+ bjam "-sTOOLS=vc-7_1"
+ </screen>
+ Here <literal>vc-7_1</literal> refers to a "Toolset" (compiler system).
+ For Visual Studio 2005, use
+ <screen>
+ bjam "-sTOOLS=vc-8_0"
+ </screen>
+ To install the libraries in a common place, use
+ <screen>
+ bjam "-sTOOLS=vc-7_1" install
+ </screen>
+ (or vc-8_0 for VS 2005).
+ </para>
+ <para>
+ By default, the Boost build process installs the resulting
+ libraries + header files in
+ <literal>\boost\lib</literal>, <literal>\boost\include</literal>.
+ </para>
+ <para>
+ For more informatation about installing Boost refer to the
+ <ulink url="&url.boost.getting.started;">getting started</ulink>
+ pages.
+ </para>
+ </section>
- <chapter id="licence">
- <title>The Metaproxy Licence</title>
- <para>
- <emphasis role="strong">
- No decision has yet been made on the terms under which
- Metaproxy will be distributed.
- </emphasis>
- It is possible that, unlike
- other Index Data products, metaproxy may not be released under a
- free-software licence such as the GNU GPL. Until a decision is
- made and a public statement made, then, and unless it has been
- delivered to you other specific terms, please treat Metaproxy as
- though it were proprietary software.
- The code should not be redistributed without explicit
- written permission from the copyright holders, Index Data ApS.
- </para>
- </chapter>
+ <section id="installation.windows.libxslt">
+ <title>Libxslt</title>
+ <para>
+ <ulink url="&url.libxslt;">Libxslt</ulink> can be downloaded
+ for Windows from
+ <ulink url="&url.libxml2.download.win32;">here</ulink>.
+ </para>
+ <para>
+ Libxslt has other dependencies, but thes can all be downloaded
+ from the same site. Get the following:
+ iconv, zlib, libxml2, libxslt.
+ </para>
+ </section>
+
+ <section id="installation.windows.yaz">
+ <title>YAZ</title>
+ <para>
+ <ulink url="&url.yaz;">YAZ</ulink> can be downloaded
+ for Windows from
+ <ulink url="&url.yaz.download.win32;">here</ulink>.
+ </para>
+ </section>
+
+ <section id="installation.windows.yazplusplus">
+ <title>YAZ++</title>
+ <para>
+ Get <ulink url="&url.yazplusplus;">YAZ++</ulink> as well.
+ Version 1.0 or later is required. For now get it from
+ Index Data's
+ <ulink url="&url.snapshot.download;">Snapshot area</ulink>.
+ </para>
+ <para>
+ YAZ++ includes NMAKE makefiles, similar to those found in the
+ YAZ package.
+ </para>
+ </section>
+
+ <section id="installation.windows.metaproxy">
+ <title>Metaproxy</title>
+ <para>
+ Metaproxy is shipped with NMAKE makfiles as well - similar
+ to those found in the YAZ++/YAZ packages. Adjust this Makefile
+ to point to the proper locations of Boost, Libxslt, Libxml2,
+ zlib, iconv, yaz and yazpp.
+ </para>
+ <variablelist>
+ <varlistentry><term><literal>DEBUG</literal></term>
+ <listitem><para>
+ If set to 1, the software is
+ compiled with debugging libraries (code generation is
+ multi-threaded debug DLL).
+ If set to 0, the software is compiled with release libraries
+ (code generation is multi-threaded DLL).
+ </para></listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><literal>BOOST</literal></term>
+ <listitem>
+ <para>
+ Boost install location
+ </para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><literal>BOOST_VERSION</literal></term>
+ <listitem>
+ <para>
+ Boost version (replace . with _).
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><literal>BOOST_TOOLSET</literal></term>
+ <listitem>
+ <para>
+ Boost toolset.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><literal>LIBXSLT_DIR</literal>,
+ <literal>LIBXML2_DIR</literal> ..</term>
+ <listitem>
+ <para>
+ Specify the locations of Libxslt, libiconv, libxml2 and
+ libxslt.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ </variablelist>
+
+ <para>
+ After succesful compilation you'll find
+ <literal>metaproxy.exe</literal> in the
+ <literal>bin</literal> directory.
+ </para>
+ </section>
+
+
+ </section>
+ </chapter>
+
<chapter id="architecture">
<title>The Metaproxy Architecture</title>
<para>
The word ``filter'' is sometimes used rather loosely, in two
different ways: it may be used to mean a particular
<emphasis>type</emphasis> of filter, as when we speak of ``the
- auth_simplefilter'' or ``the multi filter''; or it may be used
+ auth_simple filter'' or ``the multi filter''; or it may be used
to be a specific <emphasis>instance</emphasis> of a filter
within a Metaproxy configuration. For example, a single
configuration will often contain multiple instances of the
as part of Metaproxy, and others may be provided by third parties
and dynamically loaded. They all conform to the same simple API
of essentially two methods: <function>configure()</function> is
- called at startup time, and is passed a DOM tree representing that
+ called at startup time, and is passed an XML DOM tree representing that
part of the configuration file that pertains to this filter
instance: it is expected to walk that tree extracting relevant
information; and <function>process()</function> is called every
others are sinks: they consume packages and return a result
(<literal>z3950_client</literal>,
<literal>backend_test</literal>,
+ <literal>bounce</literal>,
<literal>http_file</literal>);
the others are true filters, that read, process and pass on the
packages they are fed
The filters are here listed in alphabetical order:
</para>
+<!--
+
+### New filters:
+
+New virt_db-alike that does inteligent peer choice, explain merging,
+adds FD&N to explain. Keeps init responses (like "virt_db Classic"),
+makes routing choices based on local explain knowledge. Ref IDDI
+paper.
+
+Filter to convert Explain Classic to ZeeRex.
+
+CQL2PQF (which needs augmented ZeeRex) - MARC for Talis.
+
+SRU2Z39.50 (ditto).
+
+Figure out what additional information we need in:
+ ZeeRex (check against D3.1)
+ Init request (e.g. loop detection)
+ Query package (e.g. number of hops)
+ Query response (e.g. record source)
+
+-->
+
<section>
<title><literal>auth_simple</literal>
(mp::filter::AuthSimple)</title>
<title><literal>backend_test</literal>
(mp::filter::Backend_test)</title>
<para>
- A sink that provides dummy responses in the manner of the
+ A partial sink that provides dummy responses in the manner of the
<literal>yaz-ztest</literal> Z39.50 server. This is useful only
for testing. Seriously, you don't need this. Pretend you didn't
even read this section.
</section>
<section>
+ <title><literal>bounce</literal>
+ (mp::filter::Bounce)</title>
+ <para>
+ A sink that swallows <emphasis>all packages</emphasis>,
+ and returns them almost unprocessed.
+ It never sends any package of any type further down the row, but
+ sets Z39.50 packages to Z_Close, and HTTP_Request packages to
+ HTTP_Response err code 400 packages, and adds a suitable bounce
+ message.
+ The bounce filter is usually added at end of each filter chain
+ config.xml to prevent infinite hanging of for example HTTP
+ requests packages when only the Z39.50 client partial sink
+ filter is found in the
+ route.
+ </para>
+ </section>
+
+ <section>
<title><literal>frontend_net</literal>
(mp::filter::FrontendNet)</title>
<para>
<title><literal>http_file</literal>
(mp::filter::HttpFile)</title>
<para>
- A sink that returns the contents of files from the local
- filesystem in response to HTTP requests. (Yes, Virginia, this
+ A partial sink which swallows only HTTP_Request packages, and
+ returns the contents of files from the local
+ filesystem in response to HTTP requests.
+ It lets Z39.50 packages and all other forthcoming package types
+ pass untouched.
+ (Yes, Virginia, this
does mean that Metaproxy is also a Web-server in its spare time. So
far it does not contain either an email-reader or a Lisp
interpreter, but that day is surely coming.)
(mp::filter::Log)</title>
<para>
Writes logging information to standard output, and passes on
- the package unchanged.
+ the package unchanged. A log file name can be specified, as well
+ as multiple different logging formats.
</para>
</section>
<title><literal>multi</literal>
(mp::filter::Multi)</title>
<para>
- Performs multicast searching.
+ Performs multi-database searching.
See
<link linkend="multidb">the extended discussion</link>
of virtual databases and multi-database searching below.
<title><literal>z3950_client</literal>
(mp::filter::Z3950Client)</title>
<para>
- Performs Z39.50 searching and retrieval by proxying the
+ A partial sink which swallows only Z39.50 packages.
+ It performs Z39.50 searching and retrieval by proxying the
packages that are passed to it. Init requests are sent to the
address specified in the <literal>VAL_PROXY</literal> otherInfo
attached to the request: this may have been specified by client,
or generated by a <literal>virt_db</literal> filter earlier in
the route. Subsequent requests are sent to the same address,
which is remembered at Init time in a Session object.
+ HTTP_Request packages and all other forthcoming package types
+ are passed untouched.
</para>
</section>
</section>
<para>
The following is a small, but complete, Metaproxy configuration
file (included in the distribution as
- <literal>metaproxy/etc/config0.xml</literal>).
+ <literal>metaproxy/etc/config1.xml</literal>).
This file defines a very simple configuration that simply proxies
- to whatever backend server the client requests, but logs each
+ to whatever back-end server the client requests, but logs each
request and response. This can be useful for debugging complex
client-server dialogues.
</para>
- <screen><![CDATA[
-<?xml version="1.0"?>
+ <screen><![CDATA[<?xml version="1.0"?>
<yp2 xmlns="http://indexdata.dk/yp2/config/1">
<start route="start"/>
<filters>
<filter refid="frontend"/>
<filter type="log"/>
<filter refid="backend"/>
+ <filter type="bounce"/>
</route>
</routes>
</yp2>
]]></screen>
<para>
It works by defining a single route, called
- <literal>start</literal>, which consists of a sequence of three
+ <literal>start</literal>, which consists of a sequence of four
filters. The first and last of these are included by reference:
their <literal><filter></literal> elements have
<literal>refid</literal> attributes that refer to filters defined
middle filter is included inline in the route.
</para>
<para>
- The three filters in the route are as follows: first, a
+ The four filters in the route are as follows: first, a
<literal>frontend_net</literal> filter accepts Z39.50 requests
from any host on port 9000; then these requests are passed through
a <literal>log</literal> filter that emits a message for each
request; they are then fed into a <literal>z3950_client</literal>
- filter, which forwards the requests to the client-specified
- backend Z39.509 server. When the response arrives, it is handed
+ filter, which forwards all Z39.50 requests to the client-specified
+ back-end Z39.509 server. Those Z39.50 packages are returned by the
+ <literal>z3950_client</literal> filter, with the response data
+ filled by the external Z39.50 server targeted.
+ All non-Z39.50 packages are passed through to the
+ <literal>bounce</literal> filter, which defitely bounces
+ everything, including fish, bananas, cold pyjamas,
+ mutton, beef and trout packages.
+ When the response arrives, it is handed
back to the <literal>log</literal> filter, which emits another
- message; and then to the front-end filter, which returns the
- response to the client.
+ message; and then to the <literal>frontend_net</literal> filter,
+ which returns the response to the client.
</para>
</section>
</chapter>
<section>
<title>Introductory notes</title>
+ <para>
+ Two of Metaproxy's filters are concerned with multiple-database
+ operations. Of these, <literal>virt_db</literal> can work alone
+ to control the routing of searches to one of a number of servers,
+ while <literal>multi</literal> can work together with
+ <literal>virt_db</literal> to perform multi-database searching, merging
+ the results into a unified result-set - ``metasearch in a box''.
+ </para>
+ <para>
+ The interaction between
+ these two filters is necessarily complex: it reflects the real,
+ irreducible complexity of multi-database searching in a protocol such
+ as Z39.50 that separates initialisation from searching, and in
+ which the database to be searched is not known at initialisation
+ time.
+ </para>
+ <para>
+ It's possible to use these filters without understanding the
+ details of their functioning and the interaction between them; the
+ next two sections of this chapter are ``HOWTO'' guides for doing
+ just that. However, debugging complex configurations will require
+ a deeper understanding, which the last two sections of this
+ chapters attempt to provide.
+ </para>
+ </section>
+
+
+ <section id="multidb.virt_db">
+ <title>Virtual databases with the <literal>virt_db</literal> filter</title>
+ <para>
+ Working alone, the purpose of the
+ <literal>virt_db</literal>
+ filter is to route search requests to one of a selection of
+ back-end databases. In this way, a single Z39.50 endpoint
+ (running Metaproxy) can provide access to several different
+ underlying services, including those that would otherwise be
+ inaccessible due to firewalls. In many useful configurations, the
+ back-end databases are local to the Metaproxy installation, but
+ the software does not enforce this, and any valid Z39.50 servers
+ may be used as back-ends.
+ </para>
+ <para>
+ For example, a <literal>virt_db</literal>
+ filter could be set up so that searches in the virtual database
+ ``lc'' are forwarded to the Library of Congress bibliographic
+ catalogue server, and searches in the virtual database ``marc''
+ are forwarded to the toy database of MARC records that Index Data
+ hosts for testing purposes. A <literal>virt_db</literal>
+ configuration to make this switch would look like this:
+ </para>
+ <screen><![CDATA[<filter type="virt_db">
+ <virtual>
+ <database>lc</database>
+ <target>z3950.loc.gov:7090/voyager</target>
+ </virtual>
+ <virtual>
+ <database>marc</database>
+ <target>indexdata.dk/marc</target>
+ </virtual>
+</filter>]]></screen>
+ <para>
+ As well as being useful in it own right, this filter also provides
+ the foundation for multi-database searching.
+ </para>
+ </section>
+
+
+ <section id="multidb.multi">
+ <title>Multi-database search with the <literal>multi</literal> filter</title>
+ <para>
+ To arrange for Metaproxy to broadcast searches to multiple back-end
+ servers, the configuration needs to include two components: a
+ <literal>virt_db</literal>
+ filter that specifies multiple
+ <literal><target></literal>
+ elements, and a subsequent
+ <literal>multi</literal>
+ filter. Here, for example, is a complete configuration that
+ broadcasts searches to both the Library of Congress catalogue and
+ Index Data's tiny testing database of MARC records:
+ </para>
+ <screen><![CDATA[<?xml version="1.0"?>
+<yp2 xmlns="http://indexdata.dk/yp2/config/1">
+ <start route="start"/>
+ <routes>
+ <route id="start">
+ <filter type="frontend_net">
+ <threads>10</threads>
+ <port>@:9000</port>
+ </filter>
+ <filter type="virt_db">
+ <virtual>
+ <database>lc</database>
+ <target>z3950.loc.gov:7090/voyager</target>
+ </virtual>
+ <virtual>
+ <database>marc</database>
+ <target>indexdata.dk/marc</target>
+ </virtual>
+ <virtual>
+ <database>all</database>
+ <target>z3950.loc.gov:7090/voyager</target>
+ <target>indexdata.dk/marc</target>
+ </virtual>
+ </filter>
+ <filter type="multi"/>
+ <filter type="z3950_client">
+ <timeout>30</timeout>
+ </filter>
+ <filter type="bounce"/>
+ </route>
+ </routes>
+</yp2>]]></screen>
+ <para>
+ (Using a
+ <literal>virt_db</literal>
+ filter that specifies multiple
+ <literal><target></literal>
+ elements but without a subsequent
+ <literal>multi</literal>
+ filter yields surprising and undesirable results, as will be
+ described below. Don't do that.)
+ </para>
+ <para>
+ Metaproxy can be invoked with this configuration as follows:
+ </para>
+ <screen>../src/metaproxy --config config-simple-multi.xml</screen>
+ <para>
+ And thereafter, Z39.50 clients can connect to the running server
+ (on port 9000, as specified in the configuration) and search in
+ any of the databases
+ <literal>lc</literal> (the Library of Congress catalogue),
+ <literal>marc</literal> (Index Data's test database of MARC records)
+ or
+ <literal>all</literal> (both of these). As an example, a session
+ using the YAZ command-line client <literal>yaz-client</literal> is
+ here included (edited for brevity and clarity):
+ </para>
+ <screen><![CDATA[$ yaz-client @:9000
+Connecting...OK.
+Z> base lc
+Z> find computer
+Search was a success.
+Number of hits: 10000, setno 1
+Elapsed: 5.521070
+Z> base marc
+Z> find computer
+Search was a success.
+Number of hits: 10, setno 3
+Elapsed: 0.060187
+Z> base all
+Z> find computer
+Search was a success.
+Number of hits: 10010, setno 4
+Elapsed: 2.237648
+Z> show 1
+[marc]Record type: USmarc
+001 11224466
+003 DLC
+005 00000000000000.0
+008 910710c19910701nju 00010 eng
+010 $a 11224466
+040 $a DLC $c DLC
+050 00 $a 123-xyz
+100 10 $a Jack Collins
+245 10 $a How to program a computer
+260 1 $a Penguin
+263 $a 8710
+300 $a p. cm.
+Elapsed: 0.119612
+Z> show 2
+[VOYAGER]Record type: USmarc
+001 13339105
+005 20041229102447.0
+008 030910s2004 caua 000 0 eng
+035 $a (DLC) 2003112666
+906 $a 7 $b cbc $c orignew $d 4 $e epcn $f 20 $g y-gencatlg
+925 0 $a acquire $b 1 shelf copy $x policy default
+955 $a pc10 2003-09-10 $a pv12 2004-06-23 to SSCD; $h sj05 2004-11-30 $e sj05 2004-11-30 to Shelf.
+010 $a 2003112666
+020 $a 0761542892
+040 $a DLC $c DLC $d DLC
+050 00 $a MLCM 2004/03312 (G)
+245 10 $a 007, everything or nothing : $b Prima's official strategy guide / $c created by Kaizen Media Group.
+246 3 $a Double-O-seven, everything or nothing
+246 30 $a Prima's official strategy guide
+260 $a Roseville, CA : $b Prima Games, $c c2004.
+300 $a 161 p. : $b col. ill. ; $c 28 cm.
+500 $a "Platforms: Nintendo GameCube, Macintosh, PC, PlayStation 2 computer entertainment system, Xbox"--P. [4] of cover.
+650 0 $a Video games.
+710 2 $a Kaizen Media Group.
+856 42 $3 Publisher description $u http://www.loc.gov/catdir/description/random052/2003112666.html
+Elapsed: 0.150623
+Z>
+]]></screen>
+ <para>
+ As can be seen, the first record in the result set is from the
+ Index Data test database, and the second from the Library of
+ Congress database. The result-set continues alternating records
+ round-robin style until the point where one of the databases'
+ records are exhausted.
+ </para>
+ <para>
+ This example uses only two back-end databases; more may be used.
+ There is no limitation imposed on the number of databases that may
+ be metasearched in this way: issues of resource usage and
+ administrative complexity dictate the practical limits.
+ </para>
+ <para>
+ What happens when one of the databases doesn't respond? By default,
+ the entire multi-database search fails, and the appropriate
+ diagnostic is returned to the client. This is usually appropriate
+ during development, when technicians need maximum information, but
+ can be inconvenient in deployment, when users typically don't want
+ to be bothered with problems of this kind and prefer just to get
+ the records from the databases that are available. To obtain this
+ latter behaviour add an empty
+ <literal><hideunavailable></literal>
+ element inside the
+ <literal>multi</literal> filter:
+ </para>
+ <screen><![CDATA[ <filter type="multi">
+ <hideunavailable/>
+ </filter>]]></screen>
+ <para>
+ Under this regime, an error is reported to the client only if
+ <emphasis>all</emphasis> the databases in a multi-database search
+ are unavailable.
+ </para>
+ </section>
+
+
+ <section id="multidb.what">
+ <title>What's going on?</title>
<warning>
<title>Lark's vomit</title>
<para>
- This chapter goes into a level of technical detail that is
+ This section goes into a level of technical detail that is
probably not necessary in order to configure and use Metaproxy.
It is provided only for those who like to know how things work.
You should feel free to skip on to the next section if this one
</para>
</warning>
<para>
- Two of Metaproxy's filters are concerned with multiple-database
- operations. Of these, <literal>virt_db</literal> can work alone
- to control the routing of searches to one of a number of servers,
- while <literal>multi</literal> can work with the output of
- <literal>virt_db</literal> to perform multicast searching, merging
- the results into a unified result-set. The interaction between
- these two filters is necessarily complex: it reflecting the real,
- irreducible complexity of multicast searching in a protocol such
- as Z39.50 that separates initialisation from searching, and in
- which the database to be searched is not known at initialisation
- time.
- </para>
- <para>
Hold on tight - this may get a little hairy.
</para>
<para>
>the HTTP 1.1 specification</ulink>.
</para>
<para>
- The role of the <literal>virt_db</literal> filter is to rewrite
- this otherInfo packet dependent on the virtual database that the
- client wants to search. For example, a <literal>virt_db</literal>
- filter could be set up so that searches in the virtual database
- ``lc'' are forwarded to the Library of Congress server, and
- searches in the virtual database ``id'' are forwarded to the toy
- GILS database that Index Data hosts for testing purposes. A
- <literal>virt_db</literal> configuration to make this switch would
- look like this:
+ Within Metaproxy, Search requests that are part of the same
+ session as an Init request that carries a
+ <literal>VAL_PROXY</literal> otherInfo are also annotated with the
+ same information. The role of the <literal>virt_db</literal>
+ filter is to rewrite this otherInfo packet dependent on the
+ virtual database that the client wants to search.
</para>
- <screen><![CDATA[
- <filter type="virt_db">
- <virtual>
- <database>lc</database>
- <target>z3950.loc.gov:7090/Voyager</target>
- </virtual>
- <virtual>
- <database>id</database>
- <target>indexdata.dk/gils</target>
- </virtual>
- </filter>]]></screen>
<para>
When Metaproxy receives a Z39.50 Init request from a client, it
doesn't immediately forward that request to the back-end server.
Why not? Because it doesn't know <emphasis>which</emphasis>
- back-end server to forward it to until the client sends a search
+ back-end server to forward it to until the client sends a Search
request that specifies the database that it wants to search in.
Instead, it just treasures the Init request up in its heart; and,
later, the first time the client does a search on one of the
<literal>frontend_net</literal> filter. The
<literal>virt_db</literal> filter knows nothing about it; in
fact, because the Init request that is received from the client
- doesn't get forwarded until a Search reqeust is received, the
+ doesn't get forwarded until a Search request is received, the
<literal>virt_db</literal> filter (and the
<literal>z3950_client</literal> filter behind it) doesn't even get
invoked at Init time. The <emphasis>only</emphasis> thing that a
<literal>VAL_PROXY</literal> otherInfo in the requests that pass
through it.
</para>
+ <para>
+ It is possible for a <literal>virt_db</literal> filter to contain
+ multiple
+ <literal><target></literal>
+ elements. What does this mean? Only that the filter will add
+ multiple <literal>VAL_PROXY</literal> otherInfo packets to the
+ Search requests that pass through it. That's because the virtual
+ DB filter is dumb, and does exactly what it's told - no more, no
+ less.
+ If a Search request with multiple <literal>VAL_PROXY</literal>
+ otherInfo packets reaches a <literal>z3950_client</literal>
+ filter, this is an error. That filter doesn't know how to deal
+ with multiple targets, so it will either just pick one and search
+ in it, or (better) fail with an error message.
+ </para>
+ <para>
+ The <literal>multi</literal> filter comes to the rescue! This is
+ the only filter that knows how to deal with multiple
+ <literal>VAL_PROXY</literal> otherInfo packets, and it does so by
+ making multiple copies of the entire Search request: one for each
+ <literal>VAL_PROXY</literal>. Each of these new copies is then
+ passed down through the remaining filters in the route. (The
+ copies are handled in parallel though the
+ spawning of new threads.) Since the copies each have only one
+ <literal>VAL_PROXY</literal> otherInfo, they can be handled by the
+ <literal>z3950_client</literal> filter, which happily deals with
+ each one individually. When the results of the individual
+ searches come back up to the <literal>multi</literal> filter, it
+ merges them into a single Search response, which is what
+ eventually makes it back to the client.
+ </para>
+ </section>
+
+
+ <section id="multidb.picture">
+ <title>A picture is worth a thousand words (but only five hundred on 64-bit architectures)</title>
+ <simpara>
+ <inlinemediaobject>
+ <imageobject>
+ <imagedata fileref="multi.pdf" format="PDF" scale="50"/>
+ </imageobject>
+ <imageobject>
+ <imagedata fileref="multi.png" format="PNG"/>
+ </imageobject>
+ <textobject>
+ <!-- Fall back if none of the images can be used -->
+ <phrase>
+ [Here there should be a diagram showing the progress of
+ packages through the filters during a simple virtual-database
+ search and a multi-database search, but is seems that your
+ toolchain has not been able to include the diagram in this
+ document. This is because of LaTeX suckage. Time to move to
+ OpenOffice. Yes, really.]
+ </phrase>
+ </textobject>
+<!-- ### This used to work with an older version of DocBook
+ <caption>
+ <para>Caption: progress of packages through filters.</para>
+ </caption>
+-->
+ </inlinemediaobject>
+ </simpara>
</section>
</chapter>
<para>
The virtual base class of all filters. The filter API is, on the
surface at least, extremely simple: two methods.
- <literal>configure()</literal> is passed a DOM tree representing
+ <literal>configure()</literal> is passed an XML DOM tree representing
that part of the configuration file that pertains to this filter
instance, and is expected to walk that tree extracting relevant
information. And <literal>process()</literal> processes a
</para>
</section>
</chapter>
-
-
-
- <chapter id="refguide">
+
+
+
+ <reference id="refguide">
<title>Reference guide</title>
- <para>
- The material in this chapter is drawn directly from the individual
- manual entries. In particular, the Metaproxy invocation section is
- available using <command>man metaproxy</command>, and the section
- on each individual filter is available using the name of the filter
- as the argument to the <command>man</command> command.
- </para>
-
-
- <section id="progref">
- <title>Metaproxy invocation</title>
- &progref;
- </section>
-
-
- <section id="filterref">
- <title>Reference guide to Metaproxy filters</title>
- &manref;
- </section>
- </chapter>
-
-
+ <para>
+ The material in this chapter is drawn directly from the individual
+ manual entries. In particular, the Metaproxy invocation section is
+ available using <command>man metaproxy</command>, and the section
+ on each individual filter is available using the name of the filter
+ as the argument to the <command>man</command> command.
+ </para>
+ &manref;
+ </reference>
+</book>
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