X-Git-Url: http://jsfdemo.indexdata.com/?a=blobdiff_plain;f=doc%2Fbook.xml;h=0b861da498d4b1f388290d3f51d35f44e5fe772d;hb=f5628ec48d43245fd435b9ef78b8a37bf1b42544;hp=74bd70d8ebf80c30dbe1fdc49c6e8fe982160d08;hpb=9e8552ead7fb4fc4d884222c5aac08dd94e3f450;p=metaproxy-moved-to-github.git
diff --git a/doc/book.xml b/doc/book.xml
index 74bd70d..0b861da 100644
--- a/doc/book.xml
+++ b/doc/book.xml
@@ -1,4 +1,4 @@
-
+
Metaproxy - User's Guide and Reference
@@ -9,11 +9,43 @@
2006
- Index Data
+ Index Data ApS
- Metaproxy - universal Z39.50/SRU router, proxy and encapsulated metasearcher
+ 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
+ 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
+ types, one for each operation: accepting Z39.50 packets, logging,
+ query transformation, multiplexing, etc. Further filter-types can
+ be added as loadable modules to extend Metaproxy functionality,
+ using the filter API.
+
+
+ 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.
+
+
+
+
+
+
+
+
+
+
@@ -22,32 +54,55 @@
Introduction
-
- Overview
-
- Metaproxy
- is a standalone program that acts as a universal router, proxy and
- encapsulated metasearcher for information retrieval protocols such
- as Z39.50 and SRU/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.
-
-
- Metaproxy is a more capable alternative to
- YAZ Proxy,
- 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.
-
-
+
+ Metaproxy
+ 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.
+
+
+ Anything goes in!
+ Anything goes out!
+ Fish, bananas, cold pyjamas,
+ Mutton, beef and trout!
+ - attributed to Cole Porter.
+
+
+ Metaproxy is a more capable alternative to
+ YAZ Proxy,
+ 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.
+
+
+ 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 metaproxy
+ program, and detailed information on each type of filter,
+ including examples.
+
@@ -56,8 +111,8 @@
The Metaproxy Licence
- No decision has yet been made on the terms under which
- Metaproxy will be distributed.
+ No decision has yet been made on the terms under which
+ Metaproxy will be distributed.
It is possible that, unlike
other Index Data products, metaproxy may not be released under a
@@ -65,11 +120,224 @@
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.
+
+ Installation
+
+ Metaproxy depends on the following tools/libraries:
+
+ YAZ++
+
+
+ This is a C++ library based on YAZ.
+
+
+
+ Libxslt
+
+ This is an XSLT processor - based on
+ Libxml2. Both Libxml2 and
+ Libxslt must be installed with the development components
+ (header files, etc.) as well as the run-time libraries.
+
+
+
+ Boost
+
+
+ The popular C++ library. Initial versions of Metaproxy
+ was built with 1.33.0. Version 1.33.1 works too.
+
+
+
+
+
+
+ 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
+ Compiler Status
+ for more information.
+
+
+ We have succesfully used Metaproxy with Boost using the compilers
+ GCC version 4.0 and
+ Microsoft Visual Studio 2003/2005.
+
+
+ Installation on Unix (from Source)
+
+ 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).
+
+
+
+ Libxml2/libxslt:
+
+
+ gunzip -c libxml2-version.tar.gz|tar xf -
+ cd libxml2-version
+ ./configure
+ make
+ su
+ make install
+
+
+ gunzip -c libxslt-version.tar.gz|tar xf -
+ cd libxslt-version
+ ./configure
+ make
+ su
+ make install
+
+
+ YAZ/YAZ++:
+
+
+ gunzip -c yaz-version.tar.gz|tar xf -
+ cd yaz-version
+ ./configure
+ make
+ su
+ make install
+
+
+ gunzip -c yazpp-version.tar.gz|tar xf -
+ cd yazpp-version
+ ./configure
+ make
+ su
+ make install
+
+
+ Boost:
+
+
+ gunzip -c boost-version.tar.gz|tar xf -
+ cd boost-version
+ ./configure
+ make
+ su
+ make install
+
+
+ Metaproxy:
+
+
+ gunzip -c metaproxy-version.tar.gz|tar xf -
+ cd metaproxy-version
+ ./configure
+ make
+ su
+ make install
+
+
+
+ Installation on Debian
+
+ ### To be written
+
+
+
+
+ Installation on Windows
+
+ Compilation of Metaproxy can be done using
+ Microsoft Visual Studio.
+ We know Version 2003 works. We expect Version 2005 to
+ work as well.
+
+
+ Boost
+
+ Get Boost from its home page.
+ You also need Boost Jam (an alternative to make).
+ That's also available from this
+ home page. The files download are called something like:
+ boost_1_33-1.exe
+ and
+ boost-jam-3.1.12-1-ntx86.zip.
+ Unpack Boost Jam first. Put bjam.exe
+ 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.
+ By default, the Boost build process puts the resulting
+ libraries + header files in
+ \boost\lib, \boost\include.
+
+
+ For more informatation about installing Boost refer to the
+ getting started
+ pages.
+
+
+
+
+ Libxslt
+
+ Libxslt can be downloaded
+ for Windows from
+ here.
+
+
+ Libxslt has other dependencies, but thes can all be downloaded
+ from the same site. Get the following:
+ iconv, zlib, libxml2, libxslt.
+
+
+
+
+ YAZ
+
+ YAZ can be downloaded
+ for Windows from
+ here.
+
+
+
+
+ YAZ++
+
+ Get YAZ++ as well.
+ Version 1.0 or later is required. For now get it from
+ Index Data's
+ Snapshot area.
+
+
+ YAZ++ includes NMAKE makefiles, similar to those found in the
+ YAZ package.
+
+
+
+
+ Metaproxy
+
+ 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.
+
+
+ After succesful compilation you'll find
+ metaproxy.exe in the
+ bin directory.
+
+
+
+
+
+
The Metaproxy Architecture
@@ -137,9 +405,10 @@
different ways: it may be used to mean a particular
type of filter, as when we speak of ``the
auth_simplefilter'' or ``the multi filter''; or it may be used
- to be a specific instance of a filter within a Metaproxy
- configuration. For example, a single configuration will often
- contain multiple instances of the z3950_client filter. In
+ to be a specific instance of a filter
+ within a Metaproxy configuration. For example, a single
+ configuration will often contain multiple instances of the
+ z3950_client filter. In
operational terms, of these is a separate filter. In practice,
context always make it clear which sense of the word ``filter''
is being used.
@@ -177,7 +446,7 @@
complex data type, namely the ``package''.
- A package represents a Z39.50 or SRW/U request (whether for Init,
+ A package represents a Z39.50 or SRU/W request (whether for Init,
Search, Scan, etc.) together with information about where it came
from. Packages are created by front-end filters such as
frontend_net (see below), which reads them from
@@ -189,7 +458,7 @@
There are many kinds of filter: some that are defined statically
- as part of Metaproxy, and other that may be provided by third parties
+ 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: configure() is
called at startup time, and is passed a DOM tree representing that
@@ -220,14 +489,27 @@
-
- Individual filters
+
+ Overview of filter types
+
+ We now briefly consider each of the types of filter supported by
+ the core Metaproxy binary. This overview is intended to give a
+ flavour of the available functionality; more detailed information
+ about each type of filter is included below in
+ the reference guide to Metaproxy filters.
+
The filters are here named by the string that is used as the
type attribute of a
<filter> element in the configuration
file to request them, with the name of the class that implements
- them in parentheses.
+ them in parentheses. (The classname is not needed for normal
+ configuration and use of Metaproxy; it is useful only to
+ developers.)
+
+
+ The filters are here listed in alphabetical order:
@@ -239,10 +521,13 @@
lists username:password
pairs, one per line, colon separated. When a session begins, it
is rejected unless username and passsword are supplied, and match
- a pair in the register.
-
-
- ### discuss authorisation phase
+ a pair in the register. The configuration file may also specific
+ the name of another file that is the target register: this lists
+ lists username:dbname,dbname...
+ sets, one per line, with multiple database names separated by
+ commas. When a search is processed, it is rejected unless the
+ database to be searched is one of those listed as available to
+ the user.
@@ -252,7 +537,8 @@
A sink that provides dummy responses in the manner of the
yaz-ztest Z39.50 server. This is useful only
- for testing.
+ for testing. Seriously, you don't need this. Pretend you didn't
+ even read this section.
@@ -260,10 +546,10 @@
<literal>frontend_net</literal>
(mp::filter::FrontendNet)
- A source that accepts Z39.50 and SRW connections from a port
+ A source that accepts Z39.50 connections from a port
specified in the configuration, reads protocol units, and
- feeds them into the next filter, eventually returning the
- result to the origin.
+ feeds them into the next filter in the route. When the result is
+ revceived, it is returned to the original origin.
@@ -292,8 +578,23 @@
<literal>multi</literal>
(mp::filter::Multi)
- Performs multicast searching. See the extended discussion of
- multi-database searching below.
+ Performs multi-database searching.
+ See
+ the extended discussion
+ of virtual databases and multi-database searching below.
+
+
+
+
+ <literal>query_rewrite</literal>
+ (mp::filter::QueryRewrite)
+
+ Rewrites Z39.50 Type-1 and Type-101 (``RPN'') queries by a
+ three-step process: the query is transliterated from Z39.50
+ packet structures into an XML representation; that XML
+ representation is transformed by an XSLT stylesheet; and the
+ resulting XML is transliterated back into the Z39.50 packet
+ structure.
@@ -303,8 +604,16 @@
When this is finished, it will implement global sharing of
result sets (i.e. between threads and therefore between
- clients), but it's not yet done.
+ clients), yielding performance improvements especially when
+ incoming requests are from a stateless environment such as a
+ web-server, in which the client process representing a session
+ might be any one of many. However:
+
+
+ This filter is not yet completed.
+
+
@@ -315,7 +624,8 @@
should be called nop or
passthrough?) This exists not to be used, but
to be copied - to become the skeleton of new filters as they are
- written.
+ written. As with backend_test, this is not
+ intended for civilians.
@@ -323,8 +633,14 @@
<literal>virt_db</literal>
(mp::filter::Virt_db)
- Performs virtual database selection. See the extended discussion
- of virtual databases below.
+ Performs virtual database selection: based on the name of the
+ database in the search request, a server is selected, and its
+ address added to the request in a VAL_PROXY
+ otherInfo packet. It will subsequently be used by a
+ z3950_client filter.
+ See
+ the extended discussion
+ of virtual databases and multi-database searching below.
@@ -344,12 +660,13 @@
-
+ Future directions
Some other filters that do not yet exist, but which would be
useful, are briefly described. These may be added in future
- releases.
+ releases (or may be created by third parties, as loadable
+ modules).
@@ -362,19 +679,19 @@
- srw2z3950 (filter)
+ frontend_sru (source)
- Translate SRW requests into Z39.50 requests.
+ Receive SRU (and perhaps SRW) requests.
- srw_client (sink)
+ sru2z3950 (filter)
- SRW searching and retrieval.
-
+ Translate SRU requests into Z39.50 requests.
+
@@ -386,6 +703,14 @@
+ srw_client (sink)
+
+
+ SRW searching and retrieval.
+
+
+
+ opensearch_client (sink)
@@ -410,7 +735,9 @@
its configuration file can be thought of as a program for that
interpreter. Configuration is by means of a single file, the name
of which is supplied as the sole command-line argument to the
- yp2 program.
+ metaproxy program. (See
+ the reference guide
+ below for more information on invoking Metaproxy.)
The configuration files are written in XML. (But that's just an
@@ -435,7 +762,7 @@
-
+ Overview of XML structure
All elements and attributes are in the namespace
@@ -456,15 +783,19 @@
The <start> element is empty, but carries a
route attribute, whose value is the name of
- route at which to start running - analogouse to the name of the
+ route at which to start running - analogous to the name of the
start production in a formal grammar.
If present, <filters> contains zero or more <filter>
- elements; filters carry a type attribute and
- contain various elements that provide suitable configuration for
- filters of that type. The filter-specific elements are described
- below. Filters defined in this part of the file must carry an
+ elements. Each filter carries a type attribute
+ which specifies what kind of filter is being defined
+ (frontend_net, log, etc.)
+ and contain various elements that provide suitable configuration
+ for a filter of its type. The filter-specific elements are
+ described in
+ the reference guide below.
+ Filters defined in this part of the file must carry an
id attribute so that they can be referenced
from elsewhere.
@@ -480,131 +811,71 @@
<filters> section. Alternatively, a route within a filter
may omit the refid attribute, but contain
configuration elements similar to those used for filters defined
- in the <filters> section.
+ in the <filters> section. (In other words, each filter in a
+ route may be included either by reference or by physical
+ inclusion.)
-
- Filter configuration
+
+ An example configuration
- All <filter> elements have in common that they must carry a
- type attribute whose value is one of the
- supported ones, listed in the schema file and discussed below. In
- additional, <filters>s occurring the <filters> section
- must have an id attribute, and those occurring
- within a route must have either a refid
- attribute referencing a previously defined filter or contain its
- own configuration information.
+ The following is a small, but complete, Metaproxy configuration
+ file (included in the distribution as
+ metaproxy/etc/config0.xml).
+ This file defines a very simple configuration that simply proxies
+ to whatever back-end server the client requests, but logs each
+ request and response. This can be useful for debugging complex
+ client-server dialogues.
+
+
+
+
+
+ @:9000
+
+
+
+
+
+
+
+
+
+
+
+
+]]>
- In general, each filter recognises different configuration
- elements within its element, as each filter has different
- functionality. These are as follows:
+ It works by defining a single route, called
+ start, which consists of a sequence of three
+ filters. The first and last of these are included by reference:
+ their <filter> elements have
+ refid attributes that refer to filters defined
+ within the prior <filters> section. The
+ middle filter is included inline in the route.
+
+
+ The three filters in the route are as follows: first, a
+ frontend_net filter accepts Z39.50 requests
+ from any host on port 9000; then these requests are passed through
+ a log filter that emits a message for each
+ request; they are then fed into a z3950_client
+ filter, which forwards the requests to the client-specified
+ back-end Z39.509 server. When the response arrives, it is handed
+ back to the log filter, which emits another
+ message; and then to the front-end filter, which returns the
+ response to the client.
-
-
- <literal>auth_simple</literal>
-
- <filter type="auth_simple">
- <userRegister>../etc/example.simple-auth</userRegister>
- </filter>
-
-
-
-
- <literal>backend_test</literal>
-
- <filter type="backend_test"/>
-
-
-
-
- <literal>frontend_net</literal>
-
- <filter type="frontend_net">
- <threads>10</threads>
- <port>@:9000</port>
- </filter>
-
-
-
-
- <literal>http_file</literal>
-
- <filter type="http_file">
- <mimetypes>/etc/mime.types</mimetypes>
- <area>
- <documentroot>.</documentroot>
- <prefix>/etc</prefix>
- </area>
- </filter>
-
-
-
-
- <literal>log</literal>
-
- <filter type="log">
- <message>B</message>
- </filter>
-
-
-
-
- <literal>multi</literal>
-
- <filter type="multi"/>
-
-
-
-
- <literal>session_shared</literal>
-
- <filter type="session_shared">
- ### Not yet defined
- </filter>
-
-
-
-
- <literal>template</literal>
-
- <filter type="template"/>
-
-
-
-
- <literal>virt_db</literal>
-
- <filter type="virt_db">
- <virtual>
- <database>loc</database>
- <target>z3950.loc.gov:7090/voyager</target>
- </virtual>
- <virtual>
- <database>idgils</database>
- <target>indexdata.dk/gils</target>
- </virtual>
- </filter>
-
-
-
-
- <literal>z3950_client</literal>
-
- <filter type="z3950_client">
- <timeout>30</timeout>
- </filter>
-
-
- Virtual database as multi-database searching
+ Virtual databases and multi-database searching
@@ -613,33 +884,327 @@
Two of Metaproxy's filters are concerned with multiple-database
operations. Of these, virt_db can work alone
to control the routing of searches to one of a number of servers,
- while multi can work with the output of
- virt_db to perform multicast searching, merging
- the results into a unified result-set. The interaction between
- these two filters is necessarily complex, reflecting the real
- complexity of multicast searching in a protocol such as Z39.50
- that separates initialisation from searching, with the database to
- search known only during the latter operation.
+ while multi can work together with
+ virt_db to perform multi-database searching, merging
+ the results into a unified result-set - ``metasearch in a box''.
+
+
+ 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.
- ### Much, much more to say!
+ 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.
-
-
- Module Reference
-
- The material in this chapter includes the man pages material
-
- &manref;
+
+
+ Virtual databases with the <literal>virt_db</literal> filter
+
+ Working alone, the purpose of the
+ virt_db
+ 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.
+
+
+ For example, a virt_db
+ 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 virt_db
+ configuration to make this switch would look like this:
+
+
+
+ lc
+ z3950.loc.gov:7090/voyager
+
+
+ marc
+ indexdata.dk/marc
+
+]]>
+
+ As well as being useful in it own right, this filter also provides
+ the foundation for multi-database searching.
+
+
+
+
+
+ Multi-database search with the <literal>multi</literal> filter
+
+ To arrange for Metaproxy to broadcast searches to multiple back-end
+ servers, the configuration needs to include two components: a
+ virt_db
+ filter that specifies multiple
+ <target>
+ elements, and a subsequent
+ multi
+ 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:
+
+
+
+
+
+
+
+ 10
+ @:9000
+
+
+
+ lc
+ z3950.loc.gov:7090/voyager
+
+
+ marc
+ indexdata.dk/marc
+
+
+ all
+ z3950.loc.gov:7090/voyager
+ indexdata.dk/marc
+
+
+
+
+ 30
+
+
+
+]]>
+
+ (Using a
+ virt_db
+ filter that specifies multiple
+ <target>
+ elements but without a subsequent
+ multi
+ filter yields surprising and undesirable results, as will be
+ described below. Don't do that.)
+
+
+ Metaproxy can be invoked with this configuration as follows:
+
+ ../src/metaproxy --config config-simple-multi.xml
+
+ 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
+ lc (the Library of Congress catalogue),
+ marc (Index Data's test database of MARC records)
+ or
+ all (both of these). As an example, a session
+ using the YAZ command-line client yaz-client is
+ here included (edited for brevity and clarity):
+
+ 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>
+]]>
+
+ 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.
+
+
+ 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.
+
+
+
+
+
+ What's going on?
+
+ Lark's vomit
+
+ 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
+ doesn't seem like fun.
+
+
+
+ Hold on tight - this may get a little hairy.
+
+
+ In the general course of things, a Z39.50 Init request may carry
+ with it an otherInfo packet of type VAL_PROXY,
+ whose value indicates the address of a Z39.50 server to which the
+ ultimate connection is to be made. (This otherInfo packet is
+ supported by YAZ-based Z39.50 clients and servers, but has not yet
+ been ratified by the Maintenance Agency and so is not widely used
+ in non-Index Data software. We're working on it.)
+ The VAL_PROXY packet functions
+ analogously to the absoluteURI-style Request-URI used with the GET
+ method when a web browser asks a proxy to forward its request: see
+ the
+ Request-URI
+ section of
+ the HTTP 1.1 specification.
+
+
+ The role of the virt_db filter is to rewrite
+ this otherInfo packet dependent on the virtual database that the
+ client wants to search.
+
+
+ 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 which
+ 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
+ specified virtual databases, a connection is forged to the
+ appropriate server and the Init request is forwarded to it. If,
+ later in the session, the same client searches in a different
+ virtual database, then a connection is forged to the server that
+ hosts it, and the same cached Init request is forwarded there,
+ too.
+
+
+ All of this clever Init-delaying is done by the
+ frontend_net filter. The
+ virt_db filter knows nothing about it; in
+ fact, because the Init request that is received from the client
+ doesn't get forwarded until a Search request is received, the
+ virt_db filter (and the
+ z3950_client filter behind it) doesn't even get
+ invoked at Init time. The only thing that a
+ virt_db filter ever does is rewrite the
+ VAL_PROXY otherInfo in the requests that pass
+ through it.
+
+
+ ### Describe the use of multiple VAL_PROXY
+ otherInfos, added by virt_db and used by
+ multi.
+
+
+
+
+
+ A picture is worth a thousand words (but only five hundred on 64-bit architectures)
+
+
+
+
+
+
+
+
+
+
+
+ [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.]
+
+
+
+
+
+
+
+
Writing extensions for Metaproxy
- ###
+ ### To be written
+
+
+
Classes in the Metaproxy source code
@@ -648,7 +1213,18 @@
Introductory notesStop! Do not read this!
- You won't enjoy it at all.
+ You won't enjoy it at all. You should just skip ahead to
+ the reference guide,
+ which tells
+
+ you things you really need to know, like the fact that the
+ fabulously beautiful planet Bethselamin is now so worried about
+ the cumulative erosion by ten billion visiting tourists a year
+ that any net imbalance between the amount you eat and the amount
+ you excrete whilst on the planet is surgically removed from your
+ bodyweight when you leave: so every time you go to the lavatory it
+ is vitally important to get a receipt.
This chapter contains documentation of the Metaproxy source code, and is
@@ -671,7 +1247,7 @@
-
+ Individual classes
The classes making up the Metaproxy application are here listed by
@@ -704,7 +1280,7 @@
structures, which are listed in its constructor. Merely
instantiating this class registers all the static classes. It is
for the benefit of this class that struct
- yp2_filter_struct exists, and that all the filter
+ metaproxy_1_filter_struct exists, and that all the filter
classes provide a static object of that type.
@@ -798,7 +1374,7 @@
<literal>mp::RouterChain</literal>
(<filename>router_chain.cpp</filename>)
- ###
+ ### to be written
@@ -806,7 +1382,7 @@
<literal>mp::RouterFleXML</literal>
(<filename>router_flexml.cpp</filename>)
- ###
+ ### to be written
@@ -814,7 +1390,7 @@
<literal>mp::Session</literal>
(<filename>session.cpp</filename>)
- ###
+ ### to be written
@@ -822,7 +1398,7 @@
<literal>mp::ThreadPoolSocketObserver</literal>
(<filename>thread_pool_observer.cpp</filename>)
- ###
+ ### to be written
@@ -848,7 +1424,7 @@
-
+ Other Source Files
In addition to the Metaproxy source files that define the classes
@@ -860,7 +1436,7 @@
metaproxy_prog.cpp
- The main function of the yp2 program.
+ The main function of the metaproxy program.
@@ -888,23 +1464,36 @@
plainfile.cpp,
tstdl.cpp.
-
-
-
-
- --
-
-
-
-
-
-
-
-
+
+
+
+ Reference guide
+
+ The material in this chapter is drawn directly from the individual
+ manual entries. In particular, the Metaproxy invocation section is
+ available using man metaproxy, and the section
+ on each individual filter is available using the name of the filter
+ as the argument to the man command.
+
+
+
+
+ Metaproxy invocation
+ &progref;
+
+
+
+
+ Reference guide to Metaproxy filters
+ &manref;
+
+
+
+
+