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[idzebra-moved-to-github.git] / doc / zebra.sgml

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  $Id: zebra.sgml,v 1.12 1996-01-02 08:59:15 quinn Exp $
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<article>
<title>Zebra Server - Administrators's Guide and Reference
<author>Index Data, <tt/info@index.ping.dk/
<date>$Revision: 1.12 $
<abstract>
The Zebra information server combines a versatile fielded/free-text
search engine with a Z39.50-1995 frontend to provide a powerful and flexible
information management system. This document explains the procedure for
installing and configuring the system, and outlines the possibilities
for managing data and providing Z39.50
services with the software.
</abstract>

<toc>

<sect>Introduction

<sect1>Overview

<p>
The Zebra system is a fielded free-text indexing and retrieval engine with a
Z39.50 frontend. You can use any commercial or freeware Z39.50 client
to access data stored in Zebra.

The Zebra server is our first step towards the development of a fully
configurable, open information system. Eventually, it will be paired
off with a powerful Z39.50 client to support complex information
management tasks within almost any application domain. We're making
the server available now because it's no fun to be in the open
information retrieval business all by yourself. We want to allow
people with interesting data to make their things
available in interesting ways, without having to start out
by implementing yet another protocol stack from scratch.

This document is an introduction to the Zebra system. It will tell you
how to compile the software, and how to prepare your first database.
It also explains how the server can be configured to give you the
functionality that you need.

If you find the software interesting, you should join the support
mailing-list by sending Email to <tt/zebra-request@index.ping.dk/.

<sect1>Features

<p>
This is a listof some of the most important features of the
system.

<itemize>

<item>
Supports updating - records can be added and deleted without
rebuilding the index from scratch.
The update procedure is tolerant to crashes or hard interrupts
during register updating - registers can be reconstructed following a crash.
Registers can be safely updated even while users are accessing the server.

<item>
Supports large databases - files for indices, etc. can be
automatically partitioned over multiple disks.

<item>
Supports arbitrarily complex records - base input format is an
SGML-like syntax which allows nested (structured) data elements, as
well as variant forms of data.

<item>
Supports boolean queries as well as relevance-ranking (free-text)
searching. Right truncation and masking in terms are supported, as
well as full regular expressions.

<item>
Supports multiple concrete syntaxes
for record exchange (depending on the configuration): GRS-1, SUTRS,
ISO2709 (*MARC). Records can be mapped between record syntaxes and
schema on the fly.

<item>
Protocol support:

<itemize>

<item>
Protocol facilities: Init, Search, Retrieve, Browse.

<item>
Piggy-backed presents are honored in the search-request.

<item>
Named result sets are supported.

<item>
Easily configured to support different application profiles, with
tables for attribute sets, tag sets, and abstract syntaxes.
Additional tables control facilities such as element mappings to
different schema (eg., GILS-to-USMARC).

<item>
Complex composition specifications using Espec-1 are partially
supported (simple element requests only).

<item>
Element Set Names are defined using the Espec-1 capability of the
system, and are given in configuration files as simple element
requests (and possibly variant requests).

<item>
Some variant support (not fully implemented yet).

<item>
Using the YAZ toolkit for the protocol implementation, the
server can utilise a plug-in XTI/mOSI implementation (not included) to
provide SR services over an OSI stack, as well as Z39.50 over TCP/IP.

</itemize>

</itemize>

<sect1>Future Work

<p>
This is an alfa-release of the software, to allow you to look at
it - try it out, and assess whether it can be of use to you. We expect
this version to be followed by a succession of beta-releases until we
arrive at a stable first version.

These are some of the plans that we have for the software in the near
and far future, approximately ordered after their relative importance.
Items marked with an
asterisk will be implemented before the
last beta release.

<itemize>

<item>
*Allow the system to handle other input formats. Specifically
MARC records and general, structured ASCII records (such as mail/news
files) parameterized by regular expressions.

<item>
*Complete the support for variants. Finalize support for the WAIS
retrieval methodology.

<item>
*Finalize the data element <it/include/ facility to support multimedia
data elements in records.

<item>
*Port the system to Windows NT.

<item>
Add index and data compression to save disk space.

<item>
Add more sophisticated relevance ranking mechanisms. Add support for soundex
and stemming. Add relevance feedback support.

<item>
Add Explain support.

<item>
Add support for very large records by implementing segmentation and/or
variant pieces.

<item>
Support the Item Update extended service of the protocol.

<item>
The Zebra search engine supports approximate string matching in the
index. We'd like to find a way to support and control this from RPN.

<item>
We want to add a management system that allows you to
control your databases and configuration tables from a graphical
interface. We'll probably use Tcl/Tk to stay platform-independent.

</itemize>

Programmers thrive on user feedback. If you are interested in a facility that
you don't see mentioned here, or if there's something you think we
could do better, please drop us a mail. If you think it's all really
neat, you're welcome to drop us a line saying that, too. You'll find
contact info at the end of this file.

<sect>Getting Started

<sect>Compiling the software

<p>
Zebra uses the YAZ package to implement Z39.50, so you
have to compile YAZ before going further. Specifically, Zebra uses
the YAZ header files in <tt>yaz/include/..</tt> and its public library
<tt>yaz/lib/libyaz.a</tt>.

As with YAZ, an ANSI C compiler is required in order to compile the Zebra
server system &mdash; <tt/gcc/ works fine if your own system doesn't
provide an adequate compiler.

Unpack the Zebra software. You might put Zebra in the same directory level
as YAZ, for example if YAZ is placed in ..<tt>/src/yaz-xxx</tt>, then
Zebra is placed in ..<tt>/src/zebra-yyy</tt>.

Edit the top-level <tt>Makefile</tt> in the Zebra directory in which
you specify the location of YAZ by setting make variables.
The <tt>OSILIB</tt> should be empty if YAZ wasn't compiled with
MOSI support. Some systems, such as Solaris, have separate socket
libraries and for those systems you need to specify the
<tt>NETLIB</tt> variable.

When you are done editing the <tt>Makefile</tt> type:
<tscreen><verb>
$ make
</verb></tscreen>

If successful, two executables have been created in the sub-directory
<tt/index/.
<descrip>
<tag><tt>zebrasrv</tt></tag> The Z39.50 server and search engine.
<tag><tt>zebraidx</tt></tag> The administrative tool for the search index.
</descrip>

<sect>Quick Start

<p>
This section will get you started quickly! We will try to index a few sample
GILS records that are included with the Zebra distribution. Go to the
<tt>test</tt> subdirectory. There you will find a configuration
file named <tt>zebra.cfg</tt> with the following contents:
<tscreen><verb>
# Where are the YAZ tables located.
profilePath: /usr/local/yaz

# Files that describe the attribute sets supported.
attset: bib1.att
attset: gils.att
</verb></tscreen>

Now, edit the file and set <tt>profilePath</tt> to the path of the
YAZ profile tables (sub directory <tt>tab</tt> of YAZ).

The 48 test records are located in the sub directory <tt>records</tt>.
To index these, type:
<tscreen><verb>
$ ../index/zebraidx -t grs update records
</verb></tscreen>

In the command above the option <tt>-t</tt> specified the record
type &mdash; in this case <tt>grs</tt>. The word <tt>update</tt> followed
by a directory root updates all files below that directory node.

If your indexing command was successful, you are now ready to
fire up a server. To start a server on port 2100, type:
<tscreen><verb>
$ ../index/zebrasrv tcp:@:2100
</verb></tscreen>

The Zebra index that you've just made has one database called Default. It will
return either USMARC, GRS-1, or SUTRS depending on what your client asks
for.

To test the server, you can use any Z39.50 client (1992 or later). For
instance, you can use the demo client that comes with YAZ: Just cd to
the <tt/client/ subdirectory of the YAZ distribution and type:

<tscreen><verb>
$ client tcp:localhost:2100
</verb></tscreen>

When the client has connected, you can type:

<tscreen><verb>
Z> find surficial
Z> show 1
</verb></tscreen>

The default retrieval syntax for the client is USMARC. To try other
formats for the same record, try:

<tscreen><verb>
Z>format sutrs
Z>show 1
Z>format grs-1
Z>show 1
</verb></tscreen>

If you've made it this far, there's a reasonably good chance that
you've got through the compilation OK.

<sect><heading><label id="administrating">Administrating Zebra</>

<p>
Unlike many simpler retrieval systems, Zebra supports safe, incremental
updates to an existing index.

Normally, when Zebra modifies the index it reads a number of records
that you specify.
Depending on your specifications and on the contents of each record
one the following events take place for each record:
<descrip>
<tag>Insert</tag> The record is indexed as if it never occurred
before. Either the Zebra system doesn't know how to identify the record or
Zebra can identify the record but didn't find it to be already indexed.
<tag>Modify</tag> The record has already been indexed. In this case
either the contents of the record or the location (file) of the record
indicates that it has been indexed before.
<tag>Delete</tag> The record is deleted from the index. As in the
update-case it must be able to identify the record.
</descrip>

Please note that in both the modify- and delete- case the Zebra
indexer must be able to generate a unique key that identifies the record in
question (more on this below).

To administrate the Zebra retrieval system, you run the
<tt>zebraidx</tt> program. This program supports a number of options
which are preceded by a minus, and a few commands (not preceded by
minus).

Both the Zebra administrative tool and the Z39.50 server share a
set of index files and a global configuration file. The
name of the configuration file defaults to <tt>zebra.cfg</tt>.
The configuration file includes specifications on how to index
various kinds of records and where the other configuration files
are located. <tt>zebrasrv</tt> and <tt>zebraidx</tt> <em>must</em>
be run in the same directory where the configuration file if you do
not indicate the location of the configuration file by option
<tt>-c</tt>.

<sect1><heading><label id="record-types">Record Types</>
<p>
Indexing is a per-record process, in which
either insert/modify/delete will occur. Before a record is indexed
search keys are extracted from whatever might be the layout the
original record (sgml,html,text, etc..). The Zebra system 
currently only supports SGML-like, structured records and unstructured text
records.
To specify a particular extraction process, use either the
command line option <tt>-t</tt> or specify a
<tt>recordType</tt> setting in the configuration file.

<sect1><heading><label id="configuration-file">The Zebra Configuration File</>
<p>
The Zebra configuration file, read by <tt>zebraidx</tt> and
<tt>zebrasrv</tt> defaults to <tt>zebra.cfg</tt> unless specified
by <tt>-c</tt> option.

You can edit the configuration file with a normal text editor.
Parameter names and values are seperated by colons in the file. Lines
starting with a hash sign (<tt/#/) are treated as comments.

If you manage different sets of records that each share common
caracteristics, you can organize the configuration settings for each
type into &dquot;groups&dquot;.
When <tt>zebraidx</tt> is run and you wish to address a given group
you specify that group with the <tt>-g</tt> option. In this case
settings that have the group name as their prefix will be used
by <tt>zebraidx</tt> and not default values. The default values have no prefix.

The group is written before the option itself, separated by a dot (.).
For instance, to set the record type for group <tt/public/ to <tt/grs/
(the common format for structured records)
you would write:

<tscreen><verb>
public.recordType: grs
</verb></tscreen>

To set the default value of the record type to <tt/text/ write:

<tscreen><verb>
recordType: text
</verb></tscreen>

The configuration settings are summarized below. They will be
explained further in the following sections.

<descrip>
<tag><it>group</it>recordType<it>name</it></tag>
 Specifies how records with the file extension <it>name</it> should
 be handled by the indexer. This option may also be specified
 as a command line option (<tt>-t</tt>). Note that if you do not
 specify a <it/name/, the setting applies to all files.
<tag><it>group</it>recordId</tag>
 Specifies how the record is to be identified when updated.
<tag><it>group</it>database</tag>
 Specifies the Z39.50 database name.
<tag><it>group</it>storeKeys</tag>
 Specifies whether key information should be saved for a given
 group of records. If you plan to update/delete this type of
 records later this should be specified as 1; otherwise it
 should be 0 (default).
<tag><it>group</it>storeData</tag>
 Specifies whether the records should be stored internally
 in the Zebra system files. If you want to maintain the raw records yourself,
 this option should be false (0). If you want Zebra to take care of the records
 for you, it should be true(1).
<tag>register</tag> 
 Specifies the location of the various files that Zebra uses to represent
 your system.
<tag>tempSetPath</tag>
 Specifies the directory that the server uses for temporary result sets.
 If not specified <tt>/tmp</tt> will be used.
<tag>profilePath</tag>
 Specifies the location of profile specification paths.
<tag>attset</tag> 
 Specifies the filename(s) of attribute set files for use in
 searching. At least the Bib-1 set should be loaded (<tt/bib1.att/).
 The <tt/profilePath/ setting is used to search for attribute set
 files.
</descrip>

<sect1>Locating Records
<p>
The default behaviour of the Zebra system is to reference the
records from their original location, i.e. where they were found when you
ran <tt/zebraidx/.

If your input files are temporary - for example if you retrieve
your records from an outside source, or if they where temporarily mounted on a CD-ROM,
you may want Zebra to make an internal copy of them. To do this,
you specify 1 (true) in the <tt>storedata</tt> setting. When
the Z39.50 server retrieves the records they will be read from the
internal file structures of the system.

<sect1>Indexing with no Record IDs (Simple Indexing)

<p>
If you have a set of records that you <em/never/ wish to delete
or modify you may find &dquot;indexing without records IDs&dquot; convenient.
This indexing method uses less space than the other methods and
is simple to use. 

To use this method, you simply don't provide the <tt>recordId</tt> entry
for the group of files that you index. To add a set of records you use
<tt>zebraidx</tt> with the <tt>update</tt> command. The
<tt>update</tt> command will always add all of the records to the index
because Zebra doesn't know how to match the new set of records with
existing records.

Consider a system in which you have a group of text files called
<tt>simple</tt>. That group of records should belong to a Z39.50 database
called <tt>textbase</tt>. The following <tt/zebra.cfg/ file will suffice:

<tscreen><verb>
profilePath: /usr/local/yaz
attset: bib1.att
simple.recordType: text
simple.database: textbase
</verb></tscreen>

Since the existing records in an index can not be addressed by their
IDs, it is impossible to delete or modify records when using this method.

<sect1>Indexing with File Record IDs

<p>
If you have a set of external records that you wish to index you may
use the file key feature of the Zebra system. In short, the file key
methodology uses the paths of the files containing records as their
unique identifiers. To perform indexing of a directory with file keys,
again, you specify the top-level directory after the <tt>update</tt>
command. The command will recursively traverse the directories and
compare each with whatever have been indexed before in the same
directory. If a file is new (not in the previous version of the
directory) it is inserted into the registers; if a file was already
indexed and it has been modified since the last insertionm, the index
is also modified; if a file has been removed since the last visit, it
is deleted from the index.

The resulting system is easy to administer. To delete a record
you simply have to delete the corresponding file (say, with the
<tt/rm/ command). 
To force update of a given file, you may use the <tt>touch</tt>
command. And to add files create new files (or directories with files).
For your changes to take effect in the register you must run <tt>zebraidx</tt> with
the same directory root again.

To use this method, you must specify <tt>file</tt> as the value
of <tt>recordId</tt> in the configuration file. In addition, you
should set <tt>storeKeys</tt> to <tt>1</tt>, since the Zebra
indexer must save additional information about the keys to each record in order to
modify the indices correctly at a later time.

For example, to update group <tt>esdd</tt> records below
<tt>/home/grs</tt> you could type:
<tscreen><verb>
$ zebraidx -g esdd update /home/grs
</verb></tscreen>

The corresponding configuration file includes:
<tscreen><verb>
esdd.recordId: file
esdd.recordType: grs
esdd.storeKeys: 1
</verb></tscreen>

<em>Important note: You cannot start out with a group of records with simple
indexing (no record IDs as in the previous section) and then later
enable file record Ids. Zebra must know from the first time that you
index the group that
the files should be indexed with file record IDs.
</em>

You cannot explicitly delete records when using this method (using the
<bf/delete/ command to <tt/zebraidx/. Instead
you have to delete the files from the file system (or remove them)
and then run <tt>zebraidx</tt> with the <bf/update/ command again.

<sect1>Indexing with General Record IDs
<p>
When using this method you construct an (almost) arbritrary, internal
record key based on the contents of the record itself and other system
information. If you have a group of records that associates an ID with
each record, this method is convenient. For example, the record may
contain a title or a ID-number - unique within the group. In either
case you specify the Z39.50 attribute set and use-attribute location
in which this information is stored, and the system looks at this
field to determine the identity of the record.

As before, the record ID is defined by the <tt>recordId</tt> setting
in the configuration file. The value of the record ID specification
consists of one or more tokens separated by whitespace. The resulting
ID is
represented in the index by concatenating the tokens and separating them by
ASCII value (1).

There are three kinds of tokens:
<descrip>
<tag>Internal record info</tag> The token refers to a key that is
extracted from the record. The syntax of this token is
 <tt/(/ <em/set/ <tt/,/ <em/use/ <tt/)/, where <em/set/ is the
attribute set ordinal number and <em/use/ is the use value of the attribute.
<tag>System variable</tag> The system variables are preceded by
<verb>$</verb> and immediately followed by the system variable name, which
may one of
 <descrip>
 <tag>group</tag> Group name.
 <tag>database</tag> Current database specified.
 <tag>type</tag> Record type.
 </descrip>
<tag>Constant string</tag> A string used as part of the ID &mdash; surrounded
 by single- or double quotes.
</descrip>

The sample GILS records that come with the Zebra distribution contain a
unique ID
in the Control-Identifier field. This field is mapped to the Bib-1
use attribute 1007. To use this field as a record id, specify
<tt>(1,1007)</tt> as the value of the <tt>recordId</tt> in the
configuration file. If you have other record types that uses
the same field for a different purpose, you might add the record type (or group or database name)
to the record id of the gils records as well, to prevent matches
with other types of records. In this case the recordId might be
set like this:
<tscreen><verb>
gils.recordId: $type (1,1007)
</verb></tscreen>

As for the file record id case described in the previous section
updating your system is simply a matter of running <tt>zebraidx</tt>
with the <tt>update</tt> command. However, the update with general
keys is considerably slower than with file record IDs, since all files
visited must be (re)read to find their IDs. 

You may have noticed that when using the general record IDs
method, you can only add or modify existing records with the <tt>update</tt>
command. If you wish to delete records, you must use the,
<tt>delete</tt> command, with a directory as a parameter.
This will remove all records that match the files below that root
directory.

<sect1><heading><label id="register-location">Register Location</>

<p>
Normally, the index files that form dictionaries, inverted
files, record info, etc., are stored in the directory where you run
<tt>zebraidx</tt>. If you wish to store these, possibly large, files
somewhere else, you must add the <tt>register</tt> entry to the
configuration file. Furthermore, the Zebra system allows its file
structures to
span multiple file systems, which is useful if a very large number of
records are stored.

The value <tt>register</tt> of register is a sequence of tokens.
Each token takes the form:
<tscreen>
<em>dir</em><tt>:</tt><em>size</em>. 
</tscreen>
The <em>dir</em> specifies a directory in which index files will be
stored and the <em>size</em> specifies the maximum size of all
files in that directory. The Zebra indexer system fills each directory
in the order specified and use the next specified directories as needed.
The <em>size</em> is an integer followed by a qualifier
code, <tt>M</tt> for megabytes, <tt>k</tt> for kilobytes.

For instance, if you have two spare disks :) and the first disk is mounted
on <tt>/d1</tt> and has 200 Mb of free space and the
second, mounted on <tt>/d2</tt> has 300 Mb, you could
put this entry in your configuration file:
<tscreen><verb>
register: /d1:200M /d2:300M
</verb></tscreen>

Note that Zebra does not verify that the amount of space specified is
actually available on the directory (file system) specified - it is
your responsibility to ensure that enough space is available, and that
other applications do not use the free space. In a large production system,
it is recommended that you allocate one or more filesystem exclusively
to the Zebra register files.

<sect1><heading><label id="shadow-registers">Safe Updating - Using Shadow Registers</>

<sect2>Description

<p>
The Zebra server supports updating of the index structures. That is,
you can add records to databases managed by Zebra without rebuilding
the entire index. Since this process involves modifying structured
files with various references between blocks of data in the files, the
update process is inherently sensitive to system crashes, or to
process interruptions: Anything but a successfully completed update
process will leave the register files in an unknown state, and you
will essentially have no recourse but to re-index everything, or to
restore the register files from a backup medium. Further, while the
update process is active, users cannot be allowed to access the
system, as the contents of the register files may change unpredictably.

You can solve these problems by enabling the shadow register system in
Zebra. During the updating procedure, <tt/zebraidx/ will temporarily
write changes to the involved files in a set of &dquot;shadow
files&dquot;, without modifying the files that are accessed by the
active server processes. If the update procedure is interrupted by a
system crash or a signal, you simply repeat the procedure - the
register files have not been changed or damaged, and the partially
written shadow files are automatically deleted before the new updating
procedure commences.

At the end of the updating procedure (or in a separate operation, if
you so desire), the system enters a &dquot;commit mode&dquot;. First,
any active server processes are forced to access those blocks that
have been changed from the shadow files rather than from the main
register files; the unmodified blocks are still accessed at their
normal location (the shadow files are not a complete copy of the
register files - they only contain those parts that have actually been
modified). If the process is interrupted at any point during the
commit process, the server processes will continue to access the
shadow files until you can repeat the commit procedure and complete
the writing of data to the main register files. You can perform
multiple update operations to the registers before you commit the
changes to the system files, or you can execute the commit operation
at the end of each update operation. When the commit phase has
completed successfully, any running server processes are instructed to
switch their operations to the new, operational register, and the
temporary shadow files are deleted.

<sect2>How to Use Shadow Register Files

<p>
The first step is to allocate space on your system for the shadow
files. You do this by adding a <tt/shadow/ entry to the <tt/zebra.cfg/
file. The syntax of the <tt/shadow/ entry is exactly the same as for
the <tt/register/ entry (see section <ref name="Register Location"
id="register-location">). The location of the shadow area should be
<it/different/ from the location of the main register area (if you
have specified one - remember that the default register area is the
working directory of the server and indexing processes).

The following excerpt from a <tt/zebra.cfg/ file shows one example of
a setup that configures both the main register location and the shadow
file area. Note that two directories or partitions have been set aside
for the shadow file area. You can specify any number of directories
for each of the file areas.

<tscreen><verb>
register: /d1:500M

shadow: /scratch1:100M /scratch2:200M
</verb></tscreen>

When shadow files are enabled, an extra command is available at the
<tt/zebraidx/ command line. In order to make changes to the system
take effect for the users, you'll have to submit a
&dquot;commit&dquot; command after a (sequence of) update
operation(s). You can ask the indexer to commit the changes
immediately after the update operation:

<tscreen><verb>
$ zebraidx update /d1/records update /d2/more-records commit
</verb></tscreen>

Or you can execute multiple updates before committing the changes:

<tscreen><verb>
$ zebraidx -g books update /d1/records update /d2/more-records
$ zebraidx -g fun update /d3/fun-records
$ zebraidx commit
</verb></tscreen>

If one of the update operations above had been interrupted, the commit
operation on the last line would fail: <tt/zebraidx/ will not let you
commit changes that would destroy the running register. You'll have to
rerun all of the update operations since your last commit operation,
before you can commit the new changes.

Similarly, if the commit operation fails, <tt/zebraidx/ will not let
you start a new update operation before you have successfully repeated
the commit operation. The server processes will keep accessing the
shadow files rather than the (possibly damaged) blocks of the main
register files until the commit operation has successfully completed.

You should be aware that update operations may take slightly longer
when the shadow register system is enabled, since more file access
operations are involved. Further, while the disk space required for
the shadow register data is modest for a small update operation, you
may prefer to disable the system if you are adding a very large number
of records to an already very large database (we use the terms
<it/large/ and <it/modest/ very loosely here, since every
application's perception of size is different). To update the system
without the use of the the shadow files, simply run <tt/zebraidx/ with
the <tt/-n/ option (note that you do not have to execute the
<bf/commit/ command of <tt/zebraidx/ when you temporarily disable the
use of the shadow registers in this fashion. Note also that, just as
when the shadow registers are not enabled, server processes will be
barred from accessing the main register while the update procedure
takes place.

<sect>Running the Maintenance Interface (zebraidx)

<p>
The following is a complete reference to the command line interface to
the <tt/zebraidx/ application.

<bf/Syntax/
<tscreen><verb>
$ zebraidx &lsqb;options&rsqb; command &lsqb;directory&rsqb; ...
</verb></tscreen>
<bf/Options/
<descrip>
<tag>-t <it/type/</tag>Update all files as <it/type/. Currently, the
types supported are <tt/text/ and <tt/grs/<it/.filter/. If no
<it/filter/ is provided for the GRS (General Record Structure) type,
the canonical input format is assumed (see section <ref
id="local-representation" name="Local Representation">). Generally, it
is probably advisable to specify the record types in the
<tt/zebra.cfg/ file (see section <ref id="record-types" name="Record Types">).

<tag>-c <it/config-file/</tag>Read the configuration file
<it/config-file/ instead of <tt/zebra.cfg/.

<tag>-g <it/group/</tag>Update the files according to the group
settings for <it/group/ (see section <ref id="configuration-file"
name="The Zebra Configuration File">).

<tag>-d <it/database/</tag>The records located should be associated
with the database name <it/database/ for access through the Z39.50
server.

<tag>-d <it/mbytes/</tag>Use <it/mbytes/ of megabytes before flushing
keys to background storage. This setting affects performance when
updating large databases.

<tag>-n</tag>Disable the use of shadow registers for this operation
(see section <ref id="shadow-registers" name="Robust Updating - Using
Shadow Registers">).

<tag>-v <it/level/</tag>Set the log level to <it/level/. <it/level/
should be one of <tt/none/, <tt/debug/, and <tt/all/.

</descrip>

<bf/Commands/
<descrip>
<tag>Update <it/directory/</tag>Update the register with the files
contained in <it/directory/. If no directory is provided, a list of
files is read from <tt/stdin/. See section <ref
id="administrating" name="Administrating Zebra">.

<tag>Delete <it/directory/</tag>Remove the records corresponding to
the files found under <it/directory/ from the register.

<tag/Commit/Write the changes resulting from the last <bf/update/
commands to the register. This command is only available if the use of
shadow register files is enabled (see section <ref
id="shadow-registers" name="Robust Updating - Using Shadow
Registers">).

</descrip>

<sect>Running the Z39.50 Server (zebrasrv)

<p>
<bf/Syntax/
<tscreen><verb>
zebrasrv &lsqb;options&rsqb; &lsqb;listener-address ...&rsqb;
</verb></tscreen>

<descrip>
<tag>-a <it/APDU file/</tag> Specify a file for dumping PDUs (for diagnostic purposes).
The special name &dquot;-&dquot; sends output to <tt/stderr/.

<tag/-S/Don't fork on connection requests. This can be useful for
symbolic-level debugging. The server can only accept a single
connection in this mode.

<tag/-s/Use the SR protocol.

<tag/-z/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.

<tag>-l <it/logfile/</tag>Specify an output file for the diagnostic
messages. The default is to write this information to <tt/stderr/.

<tag>-v <it/log-level/</tag>The log level. Use a comma-separated list of members of the set
{fatal,debug,warn,log,all,none}.

<tag>-u <it/username/</tag>Set user ID. Sets the real UID of the server process to that of the
given <it/username/. It's useful if you aren't comfortable with having the
server run as root, but you need to start it as such to bind a
privileged port.
</descrip>

A <it/listener-address/ consists of a transport mode followed by a
colon (:) followed by a listener address. The transport mode is
either <tt/osi/ or <tt/tcp/.

For TCP, an address has the form

<tscreen><verb>
hostname | IP-number &lsqb;: portnumber&rsqb;
</verb></tscreen>

The port number defaults to 210 (standard Z39.50 port).

For OSI (only available if the server is compiled with XTI/mOSI
support enabled), the address form is

<tscreen><verb>
&lsqb;t-selector /&rsqb; hostname | IP-number &lsqb;: portnumber&rsqb;
</verb></tscreen>

The transport selector is given as a string of hex digits (with an even
number of digits). The default port number is 102 (RFC1006 port).

Examples

<tscreen>
<verb>
tcp:dranet.dra.com

osi:0402/dbserver.osiworld.com:3000
</verb>
</tscreen>

In both cases, the special hostname &dquot;@&dquot; 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 ports for
Z39.50 and SR over OSI/RFC1006, and to drop root privileges once the
ports are bound, execute the server like this (from a root shell):

<tscreen><verb>
zebrasrv -u daemon tcp:@ -s osi:@
</verb></tscreen>

You can replace <tt/daemon/ with another user, eg. your own account, or
a dedicated IR server account.

The default behavior for <tt/zebrasrv/ is to establish a single TCP/IP
listener, for the Z39.50 protocol, on port 9999.

<sect>The Record Model

<p>
The Zebra system is designed to span a wide range of data management
applications. The system can be configured to handle virtually any
kind of structured data. Each record in the system is associated with
a <it/record schema/ which lends context to the data elements of the
record. Any number of record schema can coexist in the system.
Although it may be wise to use only a single schema within
one database, the system poses no such restrictions.

Records pass through three different states during processing in the
system.

<itemize>
<item>When records are first entered into the system, they are represented
in their local, or native format. This might be SGML or HTML files,
News or Mail archives, MARC records. If the system doesn't already
know how to read the type of data you need to store, you can set up an
input filter by preparing conversion rules based on regular
expressions and a flexible scripting language (Tcl). The input filter
produces as output an internal representation:

<item>When records are processed by the system, they are represented
in a tree-structure, constructed by tagged data elements hanging off a
root node. The tagged elements may contain data or yet more tagged
elements in a recursive structure. The system performs various
actions on this tree structure (indexing, element selection, schema
mapping, etc.),

<item>Before transmitting records to the client, they are first
converted from the internal structure to a form suitable for exchange
over the network - according to the Z39.50 standard.
</itemize>

<sect1><heading><label id="local-representation">Local Representation</>

<p>
As mentioned earlier, Zebra places few restrictions on the type of
data that you can index and manage. Generally, whatever the form of
the data, it is parsed by an input filter specific to that format, and
turned into an internal structure that Zebra knows how to handle. This
process takes place whenever the record is accessed - for indexing and
retrieval.

<sect2>Canonical Input Format

<p>
Although input data can take any form, it is sometimes useful to
describe the record processing capabilities of the system in terms of
a single, canonical input format that gives access to the full
spectrum of structure and flexibility in the system. In Zebra, this
canonical format is an &dquot;SGML-like&dquot; syntax.

Consider a record describing an information resource (such a record is
sometimes known as a <it/locator record/). It might contain a field
describing the distributor of the information resource, which might in
turn be partitioned into various fields providing details about the
distributor, like this:

<tscreen><verb>
<Distributor>
    <Name> USGS/WRD &etago;Name>
    <Organization> USGS/WRD &etago;Organization>
    <Street-Address>
        U.S. GEOLOGICAL SURVEY, 505 MARQUETTE, NW
    &etago;Street-Address>
    <City> ALBUQUERQUE &etago;City>
    <State> NM &etago;State>
    <Zip-Code> 87102 &etago;Zip-Code>
    <Country> USA &etago;Country>
    <Telephone> (505) 766-5560 &etago;Telephone>
&etago;Distributor>
</verb></tscreen>

<it>NOTE: The indentation used above is used to illustrate how Zebra
interprets the expression. The indentation, in itself, has no
significance to the parser for the canonical input format, which
ignores all whitespace.</it>

The keywords surrounded by &lt;...&gt; are <it/tags/, while the
sections of text in between are the <it/data elements/. A data element
is characterized by its location in the tree that is made up by the
nested elements. Each element is terminated by a closing tag -
beginning with &etago;, and containing the same symbolic tag-name as
the corresponding opening tag. The general closing tag - &etago;&gt; -
terminates the element started by the last opening tag. The
structuring of elements is significant. The element <bf/Telephone/,
for instance, may be indexed and presented to the client differently,
depending on whether it appears inside the <bf/Distributor/ element,
or some other data element.

<sect3>Record Root

<p>
The first tag in a record describes the root node of the tree that
makes up the total record. In the canonical input format, the root tag
should contain the name of the schema that lends context to the
elements of the record (see section <ref id="internal-representation"
name="Internal Representation">). The following is a GILS record that
contains only a single element (strictly speaking, that makes it an
illegal GILS record, since the GILS profile includes several mandatory
elements - Zebra does not validate the contents of a record against
the Z39.50 profile, however):

<tscreen><verb>
<gils>
    <title>Zen and the Art of Motorcycle Maintenance&etago;title>
&etago;gils>
</verb></tscreen>

<sect3>Variants

<p>
Zebra allows you to provide individual data elements in a number of
<it/variant forms/. Examples of variant forms are textual data
elements which might appear in different languages, and images which
may appear in different formats or layouts. The variant system is
essentially a clean representation of the variant mechanism of
Z39.50-1995.

The following is an example of a title element which occurs in two
different languages.

<tscreen><verb>
<title>
  <var lang lang "eng">
    Zen and the Art of Motorcycle Maintenance&etago;>
  <var lang lang "dan">
    Zen og Kunsten at Vedligeholde en Motorcykel&etago;>
&etago;title>
</verb></tscreen>

The syntax of the <it/variant element/ is <tt>&lt;<bf/var/ <it/class
type value/&gt;</tt>. The available values for the <it/class/ and
<it/type/ fields are given by the variant set that is associated with the
current schema (see section <ref id="variant-set" name="Variant Set
File">).

Variant elements are terminated by the general end-tag &etago;>, by
the variant end-tag &etago;var>, by the appearance of another variant
tag with the same <it/class/ and <it/value/ settings, or by the
appearance of another, normal tag. In other words, the end-tags for
the variants used in the example above could have been saved.

Variant elements can be nested. The element

<tscreen><verb>
<title>
  <var lang lang "eng"><var body iana "text/plain">
    Zen and the Art of Motorcycle Maintenance
&etago;title>
</verb></tscreen>

Associates two variant components to the variant list for the title
element. Given the nesting rules described above, we could write

<tscreen><verb>
<title>
  <var body iana "text/plain>
    <var lang lang "eng">
      Zen and the Art of Motorcycle Maintenance
    <var lang lang "dan">
      Zen og Kunsten at Vedligeholde en Motorcykel
&etago;title>
</verb></tscreen>

The title element above comes in two variants. Both have the IANA body
type &dquot;text/plain&dquot;, but one is in English, and the other in
Danish.

<sect2>Input Filters

<p>
In order to handle general, text-based input formats, Zebra allows the
operator to specify filters which read individual records in their native format
and produce an internal representation that the system can
work with.

Input filters are ASCII files, generally with the suffix <tt/.flt/.
The system looks for the files in the directories given in the
<bf/profilePath/ setting in the <tt/zebra.cfg/ file.

Generally, an input filter consists of a sequence of rules, where each
rule consists of a sequence of expressions, followed by an action. The
expressions are evaluated against the contents of the input record,
and the actions normally contribute to the generation of an internal
representation of the record.

An expression can be either of the following:

<descrip>
<tag/INIT/The action associated with this expression is evaluated
exactly once in the lifetime of the application, before any records
are read. It can be used in conjunction with an action that
initializes tables or other resources that are used in the processing
of input records.

<tag/BEGIN/Matches the beginning of the record. It can be used to
initialize variables, etc. Typically, the <bf/BEGIN/ rule is also used
to establish the root node of the record.

<tag/END/Matches the end of the record - when all of the contents
of the record has been processed.

<tag>/pattern/</tag>Matches a string of characters from the input
record.

<tag/BODY/This keyword may only be used between two patterns. It
matches everything between (not including) those patterns.

<tag/FINISH/THe expression asssociated with this pattern is evaluated
once, before the application terminates. It can be used to release
system resources - typically ones allocated in the <bf/INIT/ step.

</descrip>

An action is surrounded by curly braces ({...}), and consists of a
sequence of statements. Statements may be separated by newlines or
semicolons (;). Within actions, the strings that matched the
expressions immediately preceding the action can be referred to as
$0, $1, $2, etc.

The available statements are:

<descrip>

<tag>begin <it/type &lsqb;parameter ... &rsqb;/</tag>Begin a new
data element. The type is one of the following:
<descrip>
<tag/record/Begin a new record. The parameter should be the
name of the schema that describes the structure of the record, eg.
<tt/gils/ or <tt/wais/. The <tt/begin record/ call should come before
any other call to <bf/begin/.

<tag/element/Begin a new tagged element. The parameter is the
name of the tag. If the tag is not matched anywhere in the tagsets
referenced by the current schema, it is treated as a local string
tag.

<tag/variant/Begin a new node in a variant tree. The parameters are
<it/class type value/.

</descrip>

<tag/data/Create a data element under. The concatenated arguments make
up the value of the data element. The option <tt/-text/ signals that
the layout (whitespace) of the data should be retained for
transmission. The option <tt/-element/ <it/tag/ wraps the data up in
the <it/tag/. The use of the <tt/-element/ option is equivalent to
preceding the command with a <bf/begin element/ command, and following
it with the <bf/end/ command.

<tag>end <it/&lsqb;type&rsqb;/</tag>Close a data element. If no parameter is given,
the last element on the stack is terminated. The first parameter, if
any, is a type name, similar to the <bf/begin/ statement. For the
<bf/element/ type, a tag name can be provided to terminate a specific tag.

</descrip>

The following input filter reads a Usenet news file, producing a
record in the WAIS schema.

<tscreen><verb>
BEGIN                { begin record wais }

/^From:/ BODY /$/    { data -element name $1 }
/^Subject:/ BODY /$/ { data -element title $1 }
/^Date:/ BODY /$/    { data -element lastModified $1 }
/\n\n/ BODY END      {
                        begin element bodyOfDisplay
                        begin variant body iana "text/plain"
                        data -text $1
                        end record
                     }
</verb></tscreen>

If Zebra is compiled with support for Tcl (Tool Command Language)
enabled, the statements described above are supplemented with a complete
scripting environment, including control structures (conditional
expressions and loop constructs), and powerful string manipulation
mechanisms for modifying the elements of a record. Tcl is a popular
scripting environment, with several tutorials available both online
and in hardcopy.

<it>NOTE: Tcl support is not currently available, but will be
included with the next release.</it>

<sect1><heading><label id="internal-representation">Internal Representation</>

<p>
When records are manipulated by the system, they're represented in a
tree-structure, with data elements at the leaf nodes, and tags or
variant components at the non-leaf nodes. The root-node identifies the
schema that lends context to the tagging and structuring of the
record. Imagine a simple record, consisting of a 'title' element and
an 'author' element:

<tscreen><verb>
        TITLE     "Zen and the Art of Motorcycle Maintenance"
ROOT 
        AUTHOR    "Robert Pirsig"
</verb></tscreen>

A slightly more complex record would have the author element consist
of two elements, a surname and a first name:

<tscreen><verb>
        TITLE     "Zen and the Art of Motorcycle Maintenance"
ROOT  
                  FIRST-NAME "Robert"
        AUTHOR
                  SURNAME    "Pirsig"
</verb></tscreen>

The root of the record will refer to the record schema that describes
the structuring of this particular record. The schema defines the
element tags (TITLE, FIRST-NAME, etc.) that occur in the record, as
well as the structuring (SURNAME should appear below AUTHOR, etc.). In
addition, the schema establishes element set names that are used by
the client to request a subset of the elements of a given record. The
schema may also establish rules for converting the record to a
different schema, by stating, for each element, a mapping to a
different tagging.

The following sections describe the configuration files that govern
the internal management of records. The system searches for the files
in the directories specified by the <bf/profilePath/ setting in the
<tt/zebra.cfg/ file.

<sect2>The Abstract Syntax

<p>
The abstract syntax definition (ARS) is the focal point of the
record schema description. For a given schema, it may state any
or all of the following:

<itemize>
<item>The object identifier of the Z39.50 schema associated
with the ARS, so that it can be referred to by the client.

<item>The attribute set (which can possibly be a compound of multiple
sets) which applies in the profile. This is used when indexing and
searching the records belonging to the given profile.

<item>The Tag set (again, this can consist of several different sets).
This is used when reading the records from a file, to recognize the
different tags, and when transmitting the record to the client -
mapping the tags to their numerical representation, if they are
known.

<item>The variant set which is used in the profile. This provides a
vocabulary for specifying the <it/forms/ of data that appear inside
the records.

<item>Element set names, which are a shorthand way for the client to
ask for a subset of the data elements contained in a record. Element
set names, in the retrieval module, are mapped to <it/element
specifications/, which contain information equivalent to the
<it/Espec-1/ syntax of Z39.50.

<item>Map tables, which may specify mappings to <it/other/ database
profiles, if desired.

<item>Possibly, a set of rules describing the mapping of elements to a
MARC representation.

<item>A list of element descriptions (this is the actual ARS of the
schema, in Z39.50 terms), which lists the ways in which the various
tags can be used and organized hierarchically.
</itemize>

Several of the entries above simply refer to other files, which
describe the given objects.

<sect2>The Configuration Files

<p>
This section describes the syntax and use of the various tables which
are used by the retrieval module.

The number of different file types may appear daunting at first, but
each type corresponds fairly clearly to a single aspect of the Z39.50
retrieval facilities. Further, the average database administrator
who is simply reusing an existing profile for which tables already
exist, shouldn't have to worry too much about the contents of these tables.

Generally, the files are simple ASCII files, which can be maintained
using any text editor. Blank lines, and lines beginning with a (#) are
ignored. Any characters followed by a (#) are also ignored. All other
lines contain <it/directives/, which establish some setting or value
to the system. Generally, settings are characterized by a single
keyword, identifying the setting, followed by a number of parameters.
Some settings are repeatable (r), while others may occur only once in a
file. Some settings are optional (o), whicle others again are
mandatory (m).

<sect2>The Abstract Syntax (.abs) Files

<p>
The name of this file type is slightly misleading in Z39.50 terms,
since, apart from the actual abstract syntax of the profile, it also
includes most of the other definitions that go into a database
profile.

When a record in the canonical, SGML-like format is read from a file
or from the database, the first tag of the file should reference the
profile that governs the layout of the record. If the first tag of the
record is, say, <tt>&lt;gils&gt;</tt>, the system will look for the profile
definition in the file <tt/gils.abs/. Profile definitions are cached,
so they only have to be read once during the lifespan of the current
process.

When writing your own input filters, the <bf/record-begin/ command
introduces the profile, and should always be called first thing when
introducing a new record.

The file may contain the following directives:

<descrip>
<tag>name <it/symbolic-name/</tag> (m) This provides a shorthand name or
description for the profile. Mostly useful for diagnostic purposes.

<tag>reference <it/OID-name/</tag> (m) The reference name of the OID for
the profile. The reference names can be found in the <bf/util/
module of <bf/YAZ/.

<tag>attset <it/filename/</tag> (m) The attribute set that is used for
indexing and searching records belonging to this profile.

<tag>tagset <it/filename/</tag> (o) The tag set (if any) that describe
that fields of the records.

<tag>varset <it/filename/</tag> (o) The variant set used in the profile.

<tag>maptab <it/filename/</tag> (o,r) This points to a
conversion table that might be used if the client asks for the record
in a different schema from the native one.

<tag>marc <it/filename/</tag> (o) Points to a file containing parameters
for representing the record contents in the ISO2709 syntax. Read the
description of the MARC representation facility below.

<tag>esetname <it/name filename/</tag> (o,r) Associates the
given element set name with an element selection file. If an (@) is
given in place of the filename, this corresponds to a null mapping for
the given element set name.

<tag>elm <it/path name attribute/</tag> (o,r) Adds an element
to the abstract record syntax of the schema. The <it/path/ follows the
syntax which is suggested by the Z39.50 document - that is, a sequence
of tags separated by slashes (/). Each tag is given as a
comma-separated pair of tag type and -value surrounded by parenthesis.
The <it/name/ is the name of the element, and the <it/attribute/
specifies what attribute to use when indexing the element. A ! in
place of the attribute name is equivalent to specifying an attribute
name identical to the element name. A - in place of the attribute name
specifies that no indexing is to take place for the given element.
</descrip>

<it>
NOTE: The mechanism for controlling indexing is not adequate for
complex databases, and will probably be moved into a separate
configuration table eventually.
</it>

The following is an excerpt from the abstract syntax file for the GILS
profile.

<tscreen><verb>
name gils
reference GILS-schema
attset gils.att
tagset gils.tag
varset var1.var

maptab gils-usmarc.map

# Element set names

esetname VARIANT gils-variant.est  # for WAIS-compliance
esetname B gils-b.est
esetname G gils-g.est
esetname F @

elm (1,10)              rank                        -
elm (1,12)              url                         -
elm (1,14)              localControlNumber     Local-number
elm (1,16)              dateOfLastModification Date/time-last-modified
elm (2,1)               Title                       !
elm (4,1)               controlIdentifier      Identifier-standard
elm (2,6)               abstract               Abstract
elm (4,51)              purpose                     !
elm (4,52)              originator                  - 
elm (4,53)              accessConstraints           !
elm (4,54)              useConstraints              !
elm (4,70)              availability                -
elm (4,70)/(4,90)       distributor                 -
elm (4,70)/(4,90)/(2,7) distributorName             !
elm (4,70)/(4,90)/(2,10 distributorOrganization     !
elm (4,70)/(4,90)/(4,2) distributorStreetAddress    !
elm (4,70)/(4,90)/(4,3) distributorCity             !
</verb></tscreen>

<sect2>The Attribute Set (.att) Files

<p>
This file type describes the <bf/Use/ elements of an attribute set.
It contains the following directives. 

<descrip>

<tag>name <it/symbolic-name/</tag> (m) This provides a shorthand name or
description for the attribute set. Mostly useful for diagnostic purposes.

<tag>reference <it/OID-name/</tag> (m) The reference name of the OID for
the attribute set. The reference names can be found in the <bf/util/
module of <bf/YAZ/.

<tag>ordinal <it/integer/</tag> (m) This value will be used to represent the
attribute set in the index. Care should be taken that each attribute
set has a unique ordinal value.

<tag>include <it/filename/</tag> (o,r) This directive is used to
include another attribute set as a part of the current one. This is
used when a new attribute set is defined as an extension to another
set. For instance, many new attribute sets are defined as extensions
to the <bf/bib-1/ set. This is an important feature of the retrieval
system of Z39.50, as it ensures the highest possible level of
interoperability, as those access points of your database which are
derived from the external set (say, bib-1) can be used even by clients
who are unaware of the new set.

<tag>att <it/att-value att-name &lsqb;local-value&rsqb;/</tag> (o,r) This
repeatable directive introduces a new attribute to the set. The
attribute value is stored in the index (unless a <it/local-value/ is
given, in which case this is stored). The name is used to refer to the
attribute from the <it/abstract syntax/. </descrip>

This is an excerpt from the GILS attribute set definition. Notice how
the file describing the <it/bib-1/ attribute set is referenced.

<tscreen><verb>
name gils
reference GILS-attset
include bib1.att
ordinal 2

att 2001                distributorName
att 2002                indexTermsControlled
att 2003                purpose
att 2004                accessConstraints
att 2005                useConstraints
</verb></tscreen>

<sect2>The Tag Set (.tag) Files

<p>
This file type defines the tagset of the profile, possibly by
referencing other tag sets (most tag sets, for instance, will include
tagsetG and tagsetM from the Z39.50 specification. The file may
contain the following directives.

<descrip>
<tag>name <it/symbolic-name/</tag> (m) This provides a shorthand name or
description for the tag set. Mostly useful for diagnostic purposes.

<tag>reference <it/OID-name/</tag> (o) The reference name of the OID for
the tag set. The reference names can be found in the <bf/util/
module of <bf/YAZ/. The directive is optional, since not all tag sets
are registered outside of their schema.

<tag>type <it/integer/</tag> (m) The type number of the tag within the schema
profile.

<tag>include <it/filename/</tag> (o,r) This directive is used
to include the definitions of other tag sets into the current one.

<tag>tag <it/number names type/</tag> (o,r) Introduces a new
tag to the set. The <it/number/ is the tag number as used in the protocol
(there is currently no mechanism for specifying string tags at this
point, but this would be quick work to add). The <it/names/ parameter
is a list of names by which the tag should be recognized in the input
file format. The names should be separated by slashes (/). The
<it/type/ is th recommended datatype of the tag. It should be one of
the following:
<itemize>
<item>structured
<item>string
<item>numeric
<item>bool
<item>oid
<item>generalizedtime
<item>intunit
<item>int
<item>octetstring
<item>null
</itemize>
</descrip>

The following is an excerpt from the TagsetG definition file.

<tscreen><verb>
name tagsetg
reference TagsetG
type 2

tag     1       title           string
tag     2       author          string
tag     3       publicationPlace string
tag     4       publicationDate string
tag     5       documentId      string
tag     6       abstract        string
tag     7       name            string
tag     8       date            generalizedtime
tag     9       bodyOfDisplay   string
tag     10      organization    string
</verb></tscreen>

<sect2><heading><label id="variant-set">The Variant Set (.var) Files</>

<p>
The variant set file is a straightforward representation of the
variant set definitions associated with the protocol. At present, only
the <it/Variant-1/ set is known.

These are the directives allowed in the file.

<descrip>
<tag>name <it/symbolic-name/</tag> (m) This provides a shorthand name or
description for the variant set. Mostly useful for diagnostic purposes.

<tag>reference <it/OID-name/</tag> (o) The reference name of the OID for
the variant set, if one is required. The reference names can be found
in the <bf/util/ module of <bf/YAZ/.

<tag>class <it/integer class-name/</tag> (m,r) Introduces a new
class to the variant set.

<tag>type <it/integer type-name datatype/</tag> (m,r) Addes a
new type to the current class (the one introduced by the most recent
<bf/class/ directive). The type names belong to the same name space as
the one used in the tag set definition file.
</descrip>

The following is an excerpt from the file describing the variant set
<it/Variant-1/.

<tscreen><verb>
name variant-1
reference Variant-1

class 1 variantId

  type  1       variantId               octetstring

class 2 body

  type  1       iana                    string
  type  2       z39.50                  string
  type  3       other                   string
</verb></tscreen>

<sect2>The Element Set (.est) Files

<p>
The element set specification files describe a selection of a subset
of the elements of a database record. The element selection mechanism
is equivalent to the one supplied by the <it/Espec-1/ syntax of the
Z39.50 specification. In fact, the internal representation of an
element set specification is identical to the <it/Espec-1/ structure,
and we'll refer you to the description of that structure for most of
the detailed semantics of the directives below.

<it>
NOTE: Not all of the Espec-1 functionality has been implemented yet.
The fields that are mentioned below all work as expected, unless
otherwise is noted.
</it>

The directives available in the element set file are as follows:

<descrip>
<tag>defaultVariantSetId <it/OID-name/</tag> (o) If variants are used in
the following, this should provide the name of the variantset used
(it's not currently possible to specify a different set in the
individual variant request). In almost all cases (certainly all
profiles known to us), the name <tt/Variant-1/ should be given here.

<tag>defaultVariantRequest <it/variant-request/</tag> (o) This directive
provides a default variant request for
use when the individual element requests (see below) do not contain a
variant request. Variant requests consist of a blank-separated list of
variant components. A variant compont is a comma-separated,
parenthesized triple of variant class, type, and value (the two former
values being represented as integers). The value can currently only be
entered as a string (this will change to depend on the definition of
the variant in question). The special value (@) is interpreted as a
null value, however.

<tag>simpleElement <it/path &lsqb;'variant' variant-request&rsqb;/</tag>
(o,r) This corresponds to a simple element request in <it/Espec-1/. The
path consists of a sequence of tag-selectors, where each of these can
consist of either:

<itemize>
<item>A simple tag, consisting of a comma-separated type-value pair in
parenthesis, possibly followed by a colon (:) followed by an
occurrences-specification (see below). The tag-value can be a number
or a string. If the first character is an apostrophe ('), this forces
the value to be interpreted as a string, even if it appears to be numerical.

<item>A WildThing, represented as a question mark (?), possibly
followed by a colon (:) followed by an occurrences specification (see
below).

<item>A WildPath, represented as an asterisk (*). Note that the last
element of the path should not be a wildPath (wildpaths don't work in
this version).
</itemize>

The occurrences-specification can be either the string <tt/all/, the
string <tt/last/, or an explicit value-range. The value-range is
represented as an integer (the starting point), possibly followed by a
plus (+) and a second integer (the number of elements, default being
one).

The variant-request has the same syntax as the defaultVariantRequest
above. Note that it may sometimes be useful to give an empty variant
request, simply to disable the default for a specific set of fields
(we aren't certain if this is proper <it/Espec-1/, but it works in
this implementation).
</descrip>

The following is an example of an element specification belonging to
the GILS profile.

<tscreen><verb>
simpleelement (1,10)
simpleelement (1,12)
simpleelement (2,1)
simpleelement (1,14)
simpleelement (4,1)
simpleelement (4,52)
</verb></tscreen>

<sect2><heading><label id="schema-mapping">The Schema Mapping (.map) Files</>

<p>
Sometimes, the client might want to receive a database record in
a schema that differs from the native schema of the record. For
instance, a client might only know how to process WAIS records, while
the database record is represented in a more specific schema, such as
GILS. In this module, a mapping of data to one of the MARC formats is
also thought of as a schema mapping (mapping the elements of the
record into fields consistent with the given MARC specification, prior
to actually converting the data to the ISO2709). This use of the
object identifier for USMARC as a schema identifier represents an
overloading of the OID which might not be entirely proper. However,
it represents the dual role of schema and record syntax which
is assumed by the MARC family in Z39.50.

<it>
NOTE: The schema-mapping functions are so far limited to a
straightforward mapping of elements. This should be extended with
mechanisms for conversions of the element contents, and conditional
mappings of elements based on the record contents.
</it>

These are the directives of the schema mapping file format:

<descrip>
<tag>targetName <it/name/</tag> (m) A symbolic name for the target schema
of the table. Useful mostly for diagnostic purposes.

<tag>targetRef <it/OID-name/</tag> (m) An OID name for the target schema.
This is used, for instance, by a server receiving a request to present
a record in a different schema from the native one. The name, again,
is found in the <bf/oid/ module of <bf/YAZ/.

<tag>map <it/element-name target-path/</tag> (o,r) Adds
an element mapping rule to the table.
</descrip>

<sect2>The MARC (ISO2709) Representation (.mar) Files

<p>
This file provides rules for representing a record in the ISO2709
format. The rules pertain mostly to the values of the constant-length
header of the record.

<it>NOTE: This will be described better. We're in the process of
re-evaluating and most likely changing the way that MARC records are
handled by the system.</it>

<sect1>Exchange Formats

<p>
Converting records from the internal structure to en exchange format
is largely an automatic process. Currently, the following exchange
formats are supported:

<itemize>
<item>GRS-1. The internal representation is based on GRS-1, so the
conversion here is straightforward. The system will create
applied variant and supported variant lists as required, if a record
contains variant information.

<item>SUTRS. Again, the mapping is fairly straighforward. Indentation
is used to show the hierarchical structure of the record.

<item>ISO2709-based formats (USMARC, etc.). Only records with a
two-level structure (corresponding to fields and subfields) can be
directly mapped to ISO2709. For records with a different structuring
(eg., GILS), the representation in a structure like USMARC involves a
schema-mapping (see section <ref id="schema-mapping" name="Schema
Mapping">), to an &dquot;implied&dquot; USMARC schema (implied,
because there is no formal schema which specifies the use of the
USMARC fields outside of ISO2709). The resultant, two-level record is
then mapped directly from the internal representation to ISO2709. See
the GILS schema definition files for a detailed example of this
approach.

<item>Explain. This representation is only available for records
belonging to the Explain schema.

</itemize>

<sect>License

<p>
Copyright &copy; 1995, Index Data.

All rights reserved.

Use and redistribution in source or binary form, with or without
modification, of any or all of this software and documentation is
permitted, provided that the following conditions are met:

1. This copyright and permission notice appear with all copies of the
software and its documentation. Notices of copyright or attribution
which appear at the beginning of any file must remain unchanged.

2. The names of Index Data or the individual authors may not be used to
endorse or promote products derived from this software without specific
prior written permission.

3. Source code or binary versions of this software and its
documentation may be used freely in not-for-profit applications. For
profit applications - such as providing for-pay database services,
marketing a product based in whole or in part on this software or its
documentation, or generally distributing this software or its
documentation under a different license - requires a commercial
license from Index Data. The software may be installed and used for
evaluation purposes in conjunction with a commercial application for a
trial period of no more than 60 days.

THIS SOFTWARE IS PROVIDED "AS IS" AND WITHOUT WARRANTY OF ANY KIND,
EXPRESS, IMPLIED, OR OTHERWISE, INCLUDING WITHOUT LIMITATION, ANY
WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
IN NO EVENT SHALL INDEX DATA BE LIABLE FOR ANY SPECIAL, INCIDENTAL,
INDIRECT OR CONSEQUENTIAL DAMAGES OF ANY KIND, OR ANY DAMAGES
WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER OR
NOT ADVISED OF THE POSSIBILITY OF DAMAGE, AND ON ANY THEORY OF
LIABILITY, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
OF THIS SOFTWARE.

<sect>About Index Data and the Zebra Server

<p>
Index Data is a consulting and software-development enterprise that
specialises in library and information management systems. Our
interests and expertise span a broad range of related fields, and one
of our primary, long-term objectives is the development of a powerful
information management
system with open network interfaces and hypermedia capabilities.

We make this software available free of charge for not-for-profit
purposes, as a service to the networking community, and to further
the development and use of quality software for open network
communication.

If you like this software, and would like to use all or part of it in
a commercial product, or to provide a commercial database service,
please contact us to discuss the details. We'll be happy to answer
questions about the software, and about our services in general. If
you have specific requirements to the software, we'll be glad to offer
our advice - and if you need to adapt the software to a special
purpose, our consulting services and expert knowledge of the software
is available to you at favorable rates.

<tscreen>
Index Data&nl
Ryesgade 3&nl
DK-2200 K&oslash;benhavn N&nl
</tscreen>

<p>
<tscreen><verb>
Phone: +45 3536 3672
Fax  : +45 3536 0449
Email: info@index.ping.dk
</verb></tscreen>

The <it>Random House College Dictionary</it>, 1975 edition
offers this definition of the 
word &dquot;Zebra&dquot;:

<it>
Zebra, n., any of several horselike, African mammals of the genus Equus,
having a characteristic pattern of black or dark-brown stripes on
a whitish background.
</it>

</article>