1 <chapter id="introduction">
2 <!-- $Id: introduction.xml,v 1.40 2006-09-22 12:34:45 adam Exp $ -->
3 <title>Introduction</title>
5 <section id="overview">
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 the
27 <ulink url="&url.zoom;">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.
39 <section id="features">
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/2000/2003). A binary distribution for Windows
111 <ulink url="&url.idzebra.download.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="&url.idzebra.download.debian;"/>.
129 <ulink url="&url.z39.50;">Z39.50</ulink> 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.
145 Piggy-backed presents are honored in the search request - that
146 is, a subset of the found records can be returned directly with
147 a search response, enabling search and retrieval to happen in a
154 Named result sets are supported.
160 Easily configured to support different application profiles, with
161 tables for attribute sets, tag sets, and abstract syntaxes.
162 Additional tables control facilities such as element mappings to
163 different schema (eg., GILS-to-USMARC).
169 Complex composition specifications using Espec-1 (partial support).
170 Element sets are defined using the Espec-1 capability,
171 and are specified in configuration files as simple element
172 requests (and, optionally, variant requests).
178 Multiple record syntaxes
179 for data retrieval: GRS-1, SUTRS,
180 XML, ISO2709 (MARC), etc. Records can be mapped between record syntaxes
181 and schemas on the fly.
191 <ulink url="&url.sru;">SRU</ulink> Web Service support:
197 The protocol operations <literal>explain</literal>,
198 <literal>searchRetrieve</literal> and <literal>scan</literal>
204 <ulink url="&url.cql;">CQL</ulink> to internal query model RPN
205 conversion is supported.
210 Multiple XML record formats
211 for data retrieval are supported, modelled over the GRS-1, SUTRS,
212 MARC record formats. Records can be mapped between record
213 schemas on the fly. Arbitrarily complex XSLT transformations
214 can be applied during record retrieval if one uses the
215 <literal>alvis</literal> filter module.
220 Extended RPN queries for search/retrieve and scan are supported,
221 for controlling approximate hit counts, etc.
232 <section id="introduction-apps">
233 <title>References and Zebra based Applications</title>
235 Zebra has been deployed in numerous applications, in both the
236 academic and commercial worlds, in application domains as diverse
237 as bibliographic catalogues, geospatial information, structured
238 vocabulary browsing, government information locators, civic
239 information systems, environmental observations, museum information
243 Notable applications include the following:
247 <section id="koha-ils">
248 <title>Koha free open-source ILS</title>
250 <ulink url="http://www.koha.org/">Koha</ulink> is a full-featured
251 open-source ILS, initially developed in
252 New Zealand by Katipo Communications Ltd, and first deployed in
253 January of 2000 for Horowhenua Library Trust. It is currently
254 maintained by a team of software providers and library technology
255 staff from around the globe.
258 <ulink url="http://liblime.com/">LibLime</ulink>,
259 a company that is marketing and supporting Koha, adds in
260 the new release of Koha 3.0 the Zebra
261 database server to drive its bibliographic database.
264 In early 2005, the Koha project development team began looking at
265 ways to improve MARC support and overcome scalability limitations
266 in the Koha 2.x series. After extensive evaluations of the best
267 of the Open Source textual database engines - including MySQL
268 full-text searching, PostgreSQL, Lucene and Plucene - the team
272 "Zebra completely eliminates scalability limitations, because it
273 can support tens of millions of records." explained Joshua
274 Ferraro, LibLime's Technology President and Koha's Project
275 Release Manager. "Our performance tests showed search results in
276 under a second for databases with over 5 million records on a
277 modest i386 900Mhz test server."
280 "Zebra also includes support for true boolean search expressions
281 and relevance-ranked free-text queries, both of which the Koha
282 2.x series lack. Zebra also supports incremental and safe
283 database updates, which allow on-the-fly record
284 management. Finally, since Zebra has at its heart the Z39.50
285 protocol, it greatly improves Koha's support for that critical
289 Although the bibliographic database will be moved to Zebra, Koha
290 3.0 will continue to use a relational SQL-based database design
291 for the 'factual' database. "Relational database managers have
292 their strengths, in spite of their inability to handle large
293 numbers of bibliographic records efficiently," summed up Ferraro,
294 "We're taking the best from both worlds in our redesigned Koha
298 See also LibLime's newsletter article
299 <ulink url="http://www.liblime.com/newsletter/2006/01/features/koha-earns-its-stripes/">
300 Koha Earns its Stripes</ulink>.
304 <section id="emilda-ils">
305 <title>Emilda open source ILS</title>
307 <ulink url="http://www.emilda.org/">Emilda</ulink>
308 is a complete Integrated Library System, released under the
309 GNU General Public License. It has a
310 full featured Web-OPAC, allowing comprehensive system management
311 from virtually any computer with an Internet connection, has
312 template based layout allowing anyone to alter the visual
313 appearance of Emilda, and is
314 XML based language for fast and easy portability to virtually any
316 Currently, Emilda is used at three schools in Espoo, Finland.
319 As a surplus, 100% MARC compatibility has been achieved using the
320 Zebra Server from Index Data as backend server.
324 <section id="reindex-ils">
325 <title>ReIndex.Net web based ILS</title>
327 <ulink url="http://www.reindex.net/index.php?lang=en">Reindex.net</ulink>
328 is a netbased library service offering all
329 traditional functions on a very high level plus many new
330 services. Reindex.net is a comprehensive and powerful WEB system
331 based on standards such as XML and Z39.50.
332 updates. Reindex supports MARC21, danMARC eller Dublin Core with
336 Reindex.net runs on GNU/Debian Linux with Zebra and Simpleserver
338 Data for bibliographic data. The relational database system
339 Sybase 9 XML is used for
341 Internally MARCXML is used for bibliographical records. Update
342 utilizes Z39.50 extended services.
346 <section id="dads-article-database">
347 <title>DADS - the DTV Article Database
350 DADS is a huge database of more than ten million records, totalling
351 over ten gigabytes of data. The records are metadata about academic
352 journal articles, primarily scientific; about 10% of these
353 metadata records link to the full text of the articles they
354 describe, a body of about a terabyte of information (although the
355 full text is not indexed.)
358 It allows students and researchers at DTU (Danmarks Tekniske
359 Universitet, the Technical College of Denmark) to find and order
360 articles from multiple databases in a single query. The database
361 contains literature on all engineering subjects. It's available
362 on-line through a web gateway, though currently only to registered
366 More information can be found at
367 <ulink url="http://www.dtv.dk/"/> and
368 <ulink url="http://dads.dtv.dk"/>
372 <section id="infonet-eprints">
373 <title>Infonet Eprints</title>
375 The InfoNet Eprints service from the
376 <ulink url="http://www.dtv.dk/">
377 Technical Knowledge Center of Denmark</ulink>
378 provides access to documents stored in
379 eprint/preprint servers and institutional research archives around
380 the world. The service is based on Open Archives Initiative metadata
381 harvesting of selected scientific archives around the world. These
382 open archives offer free and unrestricted access to their contents.
385 Infonet Eprints currently holds 1.4 million records from 16 archives.
386 The online search facility is found at
387 <ulink url="http://preprints.cvt.dk"/>.
391 <section id="alvis-project">
394 The <ulink url="http://www.alvis.info/alvis/">Alvis</ulink> EU
395 project run under the 6th Framework (IST-1-002068-STP)
396 is building a semantic-based peer-to-peer search engine. A
397 consortium of eleven partners from six different European
398 Community countries plus Switzerland and China contribute
399 with expertise in a broad range of specialties including network
400 topologies, routing algorithms, linguistic analysis and
404 The Zebra information retrieval indexing machine is used inside
405 the Alvis framework to
406 manage huge collections of natural language processed and
407 enhanced XML data, coming from a topic relevant web crawl.
408 In this application, Zebra swallows and manages 37GB of XML data
409 in about 4 hours, resulting in search times of fractions of
416 <title>ULS (Union List of Serials)</title>
419 has created a union catalogue for the periodicals of the
420 twenty-one constituent libraries of the University of London and
421 the University of Westminster
422 (<ulink url="http://www.m25lib.ac.uk/ULS/"/>).
423 They have achieved this using an
424 unusual architecture, which they describe as a
425 ``non-distributed virtual union catalogue''.
428 The member libraries send in data files representing their
429 periodicals, including both brief bibliographic data and summary
430 holdings. Then 21 individual Z39.50 targets are created, each
431 using Zebra, and all mounted on the single hardware server.
432 The live service provides a web gateway allowing Z39.50 searching
433 of all of the targets or a selection of them. Zebra's small
434 footprint allows a relatively modest system to comfortably host
438 More information can be found at
439 <ulink url="http://www.m25lib.ac.uk/ULS/"/>
444 <title>NLI-Z39.50 - a Natural Language Interface for Libraries</title>
446 Fernuniversität Hagen in Germany have developed a natural
447 language interface for access to library databases.
449 url="http://ki212.fernuni-hagen.de/nli/NLIintro.html"/> -->
450 In order to evaluate this interface for recall and precision, they
451 chose Zebra as the basis for retrieval effectiveness. The Zebra
452 server contains a copy of the GIRT database, consisting of more
453 than 76000 records in SGML format (bibliographic records from
454 social science), which are mapped to MARC for presentation.
457 (GIRT is the German Indexing and Retrieval Testdatabase. It is a
458 standard German-language test database for intelligent indexing
459 and retrieval systems. See
460 <ulink url="http://www.gesis.org/forschung/informationstechnologie/clef-delos.htm"/>)
463 Evaluation will take place as part of the TREC/CLEF campaign 2003
464 <ulink url="http://clef.iei.pi.cnr.it"/>.
465 <!-- or <ulink url="http://www4.eurospider.ch/CLEF/"/> -->
468 For more information, contact Johannes Leveling
469 <email>Johannes.Leveling@FernUni-Hagen.De</email>
473 <section id="various-web-indexes">
474 <title>Various web indexes</title>
476 Zebra has been used by a variety of institutions to construct
477 indexes of large web sites, typically in the region of tens of
478 millions of pages. In this role, it functions somewhat similarly
479 to the engine of google or altavista, but for a selected intranet
480 or a subset of the whole Web.
483 For example, Liverpool University's web-search facility (see on
485 <ulink url="http://www.liv.ac.uk/"/>
486 and many sub-pages) works by relevance-searching a Zebra database
487 which is populated by the Harvest-NG web-crawling software.
490 For more information on Liverpool university's intranet search
491 architecture, contact John Gilbertson
492 <email>jgilbert@liverpool.ac.uk</email>
496 has recently modified the Harvest web indexer to use Zebra as
497 its native repository engine. His comments on the switch over
498 from the old engine are revealing:
501 The first results after some testing with Zebra are very
502 promising. The tests were done with around 220,000 SOIF files,
503 which occupies 1.6GB of disk space.
506 Building the index from scratch takes around one hour with Zebra
507 where [old-engine] needs around five hours. While [old-engine]
508 blocks search requests when updating its index, Zebra can still
509 answer search requests.
511 Zebra supports incremental indexing which will speed up indexing
515 While the search time of [old-engine] varies from some seconds
516 to some minutes depending how expensive the query is, Zebra
517 usually takes around one to three seconds, even for expensive
520 Zebra can search more than 100 times faster than [old-engine]
521 and can process multiple search requests simultaneously
524 I am very happy to see such nice software available under GPL.
532 <section id="introduction-support">
533 <title>Support</title>
535 You can get support for Zebra from at least three sources.
538 First, there's the Zebra web site at
539 <ulink url="&url.idzebra;"/>,
540 which always has the most recent version available for download.
541 If you have a problem with Zebra, the first thing to do is see
542 whether it's fixed in the current release.
545 Second, there's the Zebra mailing list. Its home page at
546 <ulink url="&url.idzebra.mailinglist;"/>
547 includes a complete archive of all messages that have ever been
548 posted on the list. The Zebra mailing list is used both for
549 announcements from the authors (new
550 releases, bug fixes, etc.) and general discussion. You are welcome
551 to seek support there. Join by filling the form on the list home page.
554 Third, it's possible to buy a commercial support contract, with
555 well defined service levels and response times, from Index Data.
557 <ulink url="&url.indexdata.support;"/>
563 <section id="future">
564 <title>Future Directions</title>
567 These are some of the plans that we have for the software in the near
568 and far future, ordered approximately as we expect to work on them.
576 Improved support for XML in search and retrieval. Eventually,
577 the goal is for Zebra to pull double duty as a flexible
578 information retrieval engine and high-performance XML
579 repository. The recent addition of XPath searching is one
580 example of the kind of enhancement we're working on.
583 There is also the experimental <literal>ALVIS XSLT</literal>
584 XML input filter, which unleashes the full power of DOM based
585 XSLT transformations during indexing and record retrieval. Work
586 on this filter has been sponsored by the ALVIS EU project
587 <ulink url="http://www.alvis.info/alvis/"/>. We expect this filter to
588 mature soon, as it is planned to be included in the version 2.0
595 Finalisation and documentation of Zebra's C programming
596 API, allowing updates, database management and other functions
597 not readily expressed in Z39.50. We will also consider
598 exposing the API through SOAP.
604 Improved free-text searching. We're first and foremost octet jockeys and
605 we're actively looking for organisations or people who'd like
606 to contribute experience in relevance ranking and text
615 Programmers thrive on user feedback. If you are interested in a
616 facility that you don't see mentioned here, or if there's something
617 you think we could do better, please drop us a mail. Better still,
618 implement it and send us the patches.
621 If you think it's all really neat, you're welcome to drop us a line
622 saying that, too. You can email us on
623 <email>info@indexdata.dk</email>
624 or check the contact info at the end of this manual.
629 <!-- Keep this comment at the end of the file
634 sgml-minimize-attributes:nil
635 sgml-always-quote-attributes:t
638 sgml-parent-document: "zebra.xml"
639 sgml-local-catalogs: nil
640 sgml-namecase-general:t