1 <chapter id="introduction">
2 <!-- $Id: introduction.xml,v 1.27 2006-01-17 12:16:12 marc Exp $ -->
3 <title>Introduction</title>
6 <title>Overview</title>
9 <ulink url="http://indexdata.dk/zebra/">Zebra</ulink>
10 is a high-performance, general-purpose structured text
11 indexing and retrieval engine. It reads records in a
12 variety of input formats (eg. email, XML, MARC) and provides access
13 to them through a powerful combination of boolean search
14 expressions and relevance-ranked free-text queries.
18 Zebra supports large databases (tens of millions of records,
19 tens of gigabytes of data). It allows safe, incremental
20 database updates on live systems. Because Zebra supports
21 the industry-standard information retrieval protocol, Z39.50,
22 you can search Zebra databases using an enormous variety of
23 programs and toolkits, both commercial and free, which understand
24 this protocol. Application libraries are available to allow
25 bespoke clients to be written in Perl, C, C++, Java, Tcl, Visual
26 Basic, Python, PHP and more - see
27 <ulink url="http://zoom.z3950.org/">the ZOOM web site</ulink>
28 for more information on some of these client toolkits.
32 This document is an introduction to the Zebra system. It explains
33 how to compile the software, how to prepare your first database,
34 and how to configure the server to give you the
35 functionality that you need.
40 <title>Features</title>
43 This is an overview of some of Zebra's most important features:
51 Very large databases: logical files can be
52 automatically partitioned over multiple disks.
58 Arbitrarily complex records. The internal data format
59 is a structured format conceptually similar to XML or GRS-1,
60 which allows lists, nested structured data elements and
61 variant forms of data.
67 Robust updating - records can be added and deleted ``on the fly''
68 without rebuilding the index from scratch.
69 Records can be safely updated even while users are accessing
71 The update procedure is tolerant to crashes or hard interrupts
72 during database updating - data can be reconstructed following
79 Configurable to understand many input formats.
80 A system of input filters driven by
81 regular expressions allows most ASCII-based
82 data formats to be easily processed.
83 SGML, XML, ISO2709 (MARC), and raw text are also
90 Searching supports a powerful combination of boolean queries as
91 well as relevance-ranking (free-text) queries. Truncation,
92 masking, full regular expression matching and "approximate
93 matching" (eg. spelling mistakes) are all handled.
99 Index-only databases: data can be, and usually is, imported
100 into Zebra's own storage, but Zebra can also refer to
101 external files, building and maintaining indexes of "live"
108 Zebra is written in portable C, so it runs on most Unix-like systems
109 as well as Windows NT. A binary distribution for Windows NT is
111 <ulink url="http://ftp.indexdata.dk/pub/zebra/win32/"/>,
112 and pre-built packages are available for
116 <ulink url="http://ftp.indexdata.dk/pub/zebra/RedHat7.X/"/>
117 and Debian packages at
119 <literal>GNU/Debian Linux</literal> at
120 <ulink url="http://ftp.indexdata.dk/pub/zebra/debian/"/>.
129 Z39.50 protocol support:
136 Protocol facilities: Init, Search, Present (retrieval),
137 Segmentation (support for very large records), Delete, Scan
138 (index browsing), Sort, Close and support for the ``update''
139 Extended Service to add or replace an existing XML record.
142 You can insert/delete/replace an XML record given an
143 "external" ID. Actually this way of doing ES Update was
144 meant for an OAI application that Ian Ibbotson had in
145 mind to implement. The "update" command in YAZ client
146 implements this on the client side. My plan is to make
147 this available in ZOOM "extended" soon..
154 Piggy-backed presents are honored in the search request - that
155 is, a subset of the found records can be returned directly with
156 a search response, enabling search and retrieval to happen in a
163 Named result sets are supported.
169 Easily configured to support different application profiles, with
170 tables for attribute sets, tag sets, and abstract syntaxes.
171 Additional tables control facilities such as element mappings to
172 different schema (eg., GILS-to-USMARC).
178 Complex composition specifications using Espec-1 (partial support).
179 Element sets are defined using the Espec-1 capability,
180 and are specified in configuration files as simple element
181 requests (and, optionally, variant requests).
187 Multiple record syntaxes
188 for data retrieval: GRS-1, SUTRS,
189 XML, ISO2709 (MARC), etc. Records can be mapped between record syntaxes
190 and schemas on the fly.
201 <title>Applications</title>
203 Zebra has been deployed in numerous applications, in both the
204 academic and commercial worlds, in application domains as diverse
205 as bibliographic catalogues, geospatial information, structured
206 vocabulary browsing, government information locators, civic
207 information systems, environmental observations, museum information
211 Notable applications include the following:
215 <title>DADS - the DTV Article Database Service</title>
217 DADS is a huge database of more than ten million records, totalling
218 over ten gigabytes of data. The records are metadata about academic
219 journal articles, primarily scientific; about 10% of these
220 metadata records link to the full text of the articles they
221 describe, a body of about a terabyte of information (although the
222 full text is not indexed.)
225 It allows students and researchers at DTU (Danmarks Tekniske
226 Universitet, the Technical College of Denmark) to find and order
227 articles from multiple databases in a single query. The database
228 contains literature on all engineering subjects. It's available
229 on-line through a web gateway, though currently only to registered
233 More information can be found at
234 <ulink url="http://www.dtv.dk/help/dads/index_e.htm"/>
239 <title>NLI-Z39.50 - a Natural Language Interface for Libraries</title>
241 Fernuniversität Hagen in Germany have developed a natural
242 language interface for access to library databases.
243 <ulink url="http://ki212.fernuni-hagen.de/nli/NLIintro.html"/>
244 In order to evaluate this interface for recall and precision, they
245 chose Zebra as the basis for retrieval effectiveness. The Zebra
246 server contains a copy of the GIRT database, consisting of more
247 than 76000 records in SGML format (bibliographic records from
248 social science), which are mapped to MARC for presentation.
251 (GIRT is the German Indexing and Retrieval Testdatabase. It is a
252 standard German-language test database for intelligent indexing
253 and retrieval systems. See
254 <ulink url="http://www.gesis.org/forschung/informationstechnologie/clef-delos.htm"/>)
257 Evaluation will take place as part of the TREC/CLEF campaign 2003
258 <ulink url="http://clef.iei.pi.cnr.it or http://www4.eurospider.ch/CLEF/"/>
261 For more information, contact Johannes Leveling
262 <email>Johannes.Leveling@FernUni-Hagen.De</email>
267 <title>ULS (Union List of Serials)</title>
270 has created a union catalogue for the periodicals of the
271 twenty-one constituent libraries of the University of London and
272 the University of Westminster
273 (<ulink url="http://www.m25lib.ac.uk/ULS/"/>).
274 They have achieved this using an
275 unusual architecture, which they describe as a
276 ``non-distributed virtual union catalogue''.
279 The member libraries send in data files representing their
280 periodicals, including both brief bibliographic data and summary
281 holdings. Then 21 individual Z39.50 targets are created, each
282 using Zebra, and all mounted on the single hardware server.
283 The live service provides a web gateway allowing Z39.50 searching
284 of all of the targets or a selection of them. Zebra's small
285 footprint allows a relatively modest system to comfortably host
289 More information can be found at
290 <ulink url="http://www.m25lib.ac.uk/ULS/"/>
295 <title>Various web indexes</title>
297 Zebra has been used by a variety of institutions to construct
298 indexes of large web sites, typically in the region of tens of
299 millions of pages. In this role, it functions somewhat similarly
300 to the engine of google or altavista, but for a selected intranet
301 or a subset of the whole Web.
304 For example, Liverpool University's web-search facility (see on
306 <ulink url="http://www.liv.ac.uk/"/>
307 and many sub-pages) works by relevance-searching a Zebra database
308 which is populated by the Harvest-NG web-crawling software.
311 For more information on Liverpool university's intranet search
312 architecture, contact John Gilbertson
313 <email>jgilbert@liverpool.ac.uk</email>
317 <email>lee@arco.de</email>,
318 has recently modified the Harvest web indexer to use Zebra as
319 its native repository engine. His comments on the switch over
320 from the old engine are revealing:
323 The first results after some testing with Zebra are very
324 promising. The tests were done with around 220,000 SOIF files,
325 which occupies 1.6GB of disk space.
328 Building the index from scratch takes around one hour with Zebra
329 where [old-engine] needs around five hours. While [old-engine]
330 blocks search requests when updating its index, Zebra can still
331 answer search requests.
333 Zebra supports incremental indexing which will speed up indexing
337 While the search time of [old-engine] varies from some seconds
338 to some minutes depending how expensive the query is, Zebra
339 usually takes around one to three seconds, even for expensive
342 Zebra can search more than 100 times faster than [old-engine]
343 and can process multiple search requests simultaneously
346 I am very happy to see such nice software available under GPL.
355 <title>Support</title>
357 You can get support for Zebra from at least three sources.
360 First, there's the Zebra web site at
361 <ulink url="http://indexdata.dk/zebra/"/>,
362 which always has the most recent version available for download.
363 If you have a problem with Zebra, the first thing to do is see
364 whether it's fixed in the current release.
367 Second, there's the Zebra mailing list. Its home page at
368 <ulink url="http://indexdata.dk/mailman/listinfo/zebralist"/>
369 includes a complete archive of all messages that have ever been
370 posted on the list. The Zebra mailing list is used both for
371 announcements from the authors (new
372 releases, bug fixes, etc.) and general discussion. You are welcome
373 to seek support there. Join by sending email to
374 <email>zebra-request@indexdata.dk</email> with the word
375 <literal>subscribe</literal> in the body of the message.
378 Third, it's possible to buy a commercial support contract, with
379 well defined service levels and response times, from Index Data.
381 <ulink url="http://indexdata.dk/support/"/>
388 <title>Future Directions</title>
391 These are some of the plans that we have for the software in the near
392 and far future, ordered approximately as we expect to work on them.
400 Improved support for XML in search and retrieval. Eventually,
401 the goal is for Zebra to pull double duty as a flexible
402 information retrieval engine and high-performance XML
403 repository. The recent addition of XPath searching is one
404 example of the kind of enhancement we're working on.
410 Access to the search engine through SOAP/RPC API to allow the
411 construction of applications without requiring Z39.50 tools.
412 This will shortly be available by means of Index Data's
413 SRW-to-Z39.50 gateway, currently in beta test.
419 Finalisation and documentation of Zebra's C programming
420 API, allowing updates, database management and other functions
421 not readily expressed in Z39.50. We will also consider
422 exposing the API through SOAP.
428 Support for the use of Perl both for access to the Zebra API
429 and for building extension ``plug-ins'' such as input filters.
430 The code for this has been contributed to the source tree by
432 <email>pop@technomat.hu</email>,
433 and is in the process of being integrated and tested.
439 Improved free-text searching. We're first and foremost octet jockeys and
440 we're actively looking for organisations or people who'd like
441 to contribute experience in relevance ranking and text
450 Programmers thrive on user feedback. If you are interested in a
451 facility that you don't see mentioned here, or if there's something
452 you think we could do better, please drop us a mail. Better still,
453 implement it and send us the patches.
456 If you think it's all really neat, you're welcome to drop us a line
457 saying that, too. You can email us on
458 <email>info@indexdata.dk</email>
459 or check the contact info at the end of this manual.
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