Introduction
Overview &zebra; is a free, fast, friendly information management system. It can index records in &acro.xml;/&acro.sgml;, &acro.marc;, e-mail archives and many other formats, and quickly find them using a combination of boolean searching and relevance ranking. Search-and-retrieve applications can be written using &acro.api;s in a wide variety of languages, communicating with the &zebra; server using industry-standard information-retrieval protocols or web services. &zebra; is licensed Open Source, and can be deployed by anyone for any purpose without license fees. The C source code is open to anybody to read and change under the GPL license. &zebra; is a networked component which acts as a reliable &acro.z3950; server for both record/document search, presentation, insert, update and delete operations. In addition, it understands the &acro.sru; family of webservices, which exist in &acro.rest; &acro.get;/&acro.post; and truly &acro.soap; flavors. &zebra; is available as MS Windows 2003 Server (32 bit) self-extracting package as well as GNU/Debian Linux (32 bit and 64 bit) precompiled packages. It has been deployed successfully on other Unix systems, including Sun Sparc, HP Unix, and many variants of Linux and BSD based systems. http://www.indexdata.com/zebra/ http://ftp.indexdata.dk/pub/zebra/win32/ http://ftp.indexdata.dk/pub/zebra/debian/ &zebra; is a high-performance, general-purpose structured text indexing and retrieval engine. It reads records in a variety of input formats (e.g. email, &acro.xml;, &acro.marc;) and provides access to them through a powerful combination of boolean search expressions and relevance-ranked free-text queries. &zebra; supports large databases (tens of millions of records, tens of gigabytes of data). It allows safe, incremental database updates on live systems. Because &zebra; supports the industry-standard information retrieval protocol, &acro.z3950;, you can search &zebra; databases using an enormous variety of programs and toolkits, both commercial and free, which understand this protocol. Application libraries are available to allow bespoke clients to be written in Perl, C, C++, Java, Tcl, Visual Basic, Python, &acro.php; and more - see the &acro.zoom; web site for more information on some of these client toolkits. This document is an introduction to the &zebra; system. It explains how to compile the software, how to prepare your first database, and how to configure the server to give you the functionality that you need.
&zebra; Features Overview
&zebra; Document Model &zebra; document model Feature Availability Notes Reference Complex semi-structured Documents &acro.xml; and &acro.grs1; Documents Both &acro.xml; and &acro.grs1; documents exhibit a &acro.dom; like internal representation allowing for complex indexing and display rules and Input document formats &acro.xml;, &acro.sgml;, Text, ISO2709 (&acro.marc;) A system of input filters driven by regular expressions allows most ASCII-based data formats to be easily processed. &acro.sgml;, &acro.xml;, ISO2709 (&acro.marc;), and raw text are also supported. Document storage Index-only, Key storage, Document storage Data can be, and usually is, imported into &zebra;'s own storage, but &zebra; can also refer to external files, building and maintaining indexes of "live" collections.
&zebra; Index Scanning &zebra; index scanning Feature Availability Notes Reference Scan term suggestions Scan on a given named index returns all the indexed terms in lexicographical order near the given start term. This can be used to create drop-down menus and search suggestions. and Facetted browsing available Zebra 2.1 and allows retrieval of facets for a result set. Drill-down or refine-search partially scanning in result sets can be used to implement drill-down in search clients
&zebra; Document Presentation &zebra; document presentation Feature Availability Notes Reference Hit count yes Search results include at any time the total hit count of a given query, either exact computed, or approximative, in case that the hit count exceeds a possible pre-defined hit set truncation level. and Paged result sets yes Paging of search requests and present/display request can return any successive number of records from any start position in the hit set, i.e. it is trivial to provide search results in successive pages of any size. &acro.xml; document transformations &acro.xslt; based Record presentation can be performed in many pre-defined &acro.xml; data formats, where the original &acro.xml; records are on-the-fly transformed through any preconfigured &acro.xslt; transformation. It is therefore trivial to present records in short/full &acro.xml; views, transforming to RSS, Dublin Core, or other &acro.xml; based data formats, or transform records to XHTML snippets ready for inserting in XHTML pages. Binary record transformations &acro.marc;, &acro.usmarc;, &acro.marc21; and &acro.marcxml; post-filter record transformations Record Syntaxes Multiple record syntaxes for data retrieval: &acro.grs1;, &acro.sutrs;, &acro.xml;, ISO2709 (&acro.marc;), etc. Records can be mapped between record syntaxes and schemas on the fly. &zebra; internal metadata yes &zebra; internal document metadata can be fetched in &acro.sutrs; and &acro.xml; record syntaxes. Those are useful in client applications. &zebra; internal raw record data yes &zebra; internal raw, binary record data can be fetched in &acro.sutrs; and &acro.xml; record syntaxes, leveraging %zebra; to a binary storage system &zebra; internal record field data yes &zebra; internal record field data can be fetched in &acro.sutrs; and &acro.xml; record syntaxes. This makes very fast minimal record data displays possible.
&zebra; Sorting and Ranking &zebra; sorting and ranking Feature Availability Notes Reference Sort numeric, lexicographic Sorting on the basis of alpha-numeric and numeric data is supported. Alphanumeric sorts can be configured for different data encodings and locales for European languages. and Combined sorting yes Sorting on the basis of combined sorts ­ e.g. combinations of ascending/descending sorts of lexicographical/numeric/date field data is supported Relevance ranking TF-IDF like Relevance-ranking of free-text queries is supported using a TF-IDF like algorithm. Static pre-ranking yes Enables pre-index time ranking of documents where hit lists are ordered first by ascending static rank, then by ascending document ID.
&zebra; Live Updates &zebra; live updates Feature Availability Notes Reference Incremental and batch updates It is possible to schedule record inserts/updates/deletes in any quantity, from single individual handled records to batch updates in strikes of any size, as well as total re-indexing of all records from file system. Remote updates &acro.z3950; extended services Updates can be performed from remote locations using the &acro.z3950; extended services. Access to extended services can be login-password protected. and Live updates transaction based Data updates are transaction based and can be performed on running &zebra; systems. Full searchability is preserved during life data update due to use of shadow disk areas for update operations. Multiple update transactions at the same time are lined up, to be performed one after each other. Data integrity is preserved.
&zebra; Networked Protocols &zebra; networked protocols Feature Availability Notes Reference Fundamental operations &acro.z3950;/&acro.sru; explain, search, scan, and update &acro.z3950; protocol support yes Protocol facilities supported are: init, search, present (retrieval), Segmentation (support for very large records), delete, scan (index browsing), sort, close and support for the update Extended Service to add or replace an existing &acro.xml; record. Piggy-backed presents are honored in the search request. Named result sets are supported. Web Service support &acro.sru; The protocol operations explain, searchRetrieve and scan are supported. &acro.cql; to internal query model &acro.rpn; conversion is supported. Extended RPN queries for search/retrieve and scan are supported.
&zebra; Data Size and Scalability &zebra; data size and scalability Feature Availability Notes Reference No of records 40-60 million Data size 100 GB of record data &zebra; based applications have successfully indexed up to 100 GB of record data Scale out multiple discs Performance O(n * log N) &zebra; query speed and performance is affected roughly by O(log N), where N is the total database size, and by O(n), where n is the specific query hit set size. Average search times Even on very large size databases hit rates of 20 queries per seconds with average query answering time of 1 second are possible, provided that the boolean queries are constructed sufficiently precise to result in hit sets of the order of 1000 to 5.000 documents. Large databases 64 bit file pointers 64 file pointers assure that register files can extend the 2 GB limit. Logical files can be automatically partitioned over multiple disks, thus allowing for large databases.
&zebra; Supported Platforms &zebra; supported platforms Feature Availability Notes Reference Linux GNU Linux (32 and 64bit), journaling Reiser or (better) JFS file system on disks. NFS file systems are not supported. GNU/Debian Linux packages are available Unix tar-ball &zebra; is written in portable C, so it runs on most Unix-like systems. Usual tar-ball install possible on many major Unix systems Windows NT/2000/2003/XP &zebra; runs as well on Windows (NT/2000/2003/XP). Windows installer packages available
References and &zebra; based Applications &zebra; has been deployed in numerous applications, in both the academic and commercial worlds, in application domains as diverse as bibliographic catalogues, Geo-spatial information, structured vocabulary browsing, government information locators, civic information systems, environmental observations, museum information and web indexes. Notable applications include the following:
Koha free open-source ILS Koha is a full-featured open-source ILS, initially developed in New Zealand by Katipo Communications Ltd, and first deployed in January of 2000 for Horowhenua Library Trust. It is currently maintained by a team of software providers and library technology staff from around the globe. LibLime, a company that is marketing and supporting Koha, adds in the new release of Koha 3.0 the &zebra; database server to drive its bibliographic database. In early 2005, the Koha project development team began looking at ways to improve &acro.marc; support and overcome scalability limitations in the Koha 2.x series. After extensive evaluations of the best of the Open Source textual database engines - including MySQL full-text searching, PostgreSQL, Lucene and Plucene - the team selected &zebra;. "&zebra; completely eliminates scalability limitations, because it can support tens of millions of records." explained Joshua Ferraro, LibLime's Technology President and Koha's Project Release Manager. "Our performance tests showed search results in under a second for databases with over 5 million records on a modest i386 900Mhz test server." "&zebra; also includes support for true boolean search expressions and relevance-ranked free-text queries, both of which the Koha 2.x series lack. &zebra; also supports incremental and safe database updates, which allow on-the-fly record management. Finally, since &zebra; has at its heart the &acro.z3950; protocol, it greatly improves Koha's support for that critical library standard." Although the bibliographic database will be moved to &zebra;, Koha 3.0 will continue to use a relational SQL-based database design for the 'factual' database. "Relational database managers have their strengths, in spite of their inability to handle large numbers of bibliographic records efficiently," summed up Ferraro, "We're taking the best from both worlds in our redesigned Koha 3.0. See also LibLime's newsletter article Koha Earns its Stripes.
Kete Open Source Digital Library and Archiving software Kete is a digital object management repository, initially developed in New Zealand. Initial development has been a partnership between the Horowhenua Library Trust and Katipo Communications Ltd. funded as part of the Community Partnership Fund in 2006. Kete is purpose built software to enable communities to build their own digital libraries, archives and repositories. It is based on Ruby-on-Rails and MySQL, and integrates the &zebra; server and the &yaz; toolkit for indexing and retrieval of it's content. Zebra is run as separate computer process from the Kete application. See how Kete manages Zebra. Why does Kete wants to use Zebra?? Speed, Scalability and easy integration with Koha. Read their detailed reasoning here.
ReIndex.Net web based ILS Reindex.net is a netbased library service offering all traditional functions on a very high level plus many new services. Reindex.net is a comprehensive and powerful WEB system based on standards such as &acro.xml; and &acro.z3950;. updates. Reindex supports &acro.marc21;, dan&acro.marc; eller Dublin Core with UTF8-encoding. Reindex.net runs on GNU/Debian Linux with &zebra; and Simpleserver from Index Data for bibliographic data. The relational database system Sybase 9 &acro.xml; is used for administrative data. Internally &acro.marcxml; is used for bibliographical records. Update utilizes &acro.z3950; extended services.
DADS - the DTV Article Database Service DADS is a huge database of more than ten million records, totalling over ten gigabytes of data. The records are metadata about academic journal articles, primarily scientific; about 10% of these metadata records link to the full text of the articles they describe, a body of about a terabyte of information (although the full text is not indexed.) It allows students and researchers at DTU (Danmarks Tekniske Universitet, the Technical College of Denmark) to find and order articles from multiple databases in a single query. The database contains literature on all engineering subjects. It's available on-line through a web gateway, though currently only to registered users. More information can be found at and
ULS (Union List of Serials) The M25 Systems Team has created a union catalogue for the periodicals of the twenty-one constituent libraries of the University of London and the University of Westminster (). They have achieved this using an unusual architecture, which they describe as a ``non-distributed virtual union catalogue''. The member libraries send in data files representing their periodicals, including both brief bibliographic data and summary holdings. Then 21 individual &acro.z3950; targets are created, each using &zebra;, and all mounted on the single hardware server. The live service provides a web gateway allowing &acro.z3950; searching of all of the targets or a selection of them. &zebra;'s small footprint allows a relatively modest system to comfortably host the 21 servers. More information can be found at
Various web indexes &zebra; has been used by a variety of institutions to construct indexes of large web sites, typically in the region of tens of millions of pages. In this role, it functions somewhat similarly to the engine of Google or AltaVista, but for a selected intranet or a subset of the whole Web. For example, Liverpool University's web-search facility (see on the home page at and many sub-pages) works by relevance-searching a &zebra; database which is populated by the Harvest-NG web-crawling software. For more information on Liverpool university's intranet search architecture, contact John Gilbertson jgilbert@liverpool.ac.uk Kang-Jin Lee has recently modified the Harvest web indexer to use &zebra; as its native repository engine. His comments on the switch over from the old engine are revealing:
The first results after some testing with &zebra; are very promising. The tests were done with around 220,000 SOIF files, which occupies 1.6GB of disk space. Building the index from scratch takes around one hour with &zebra; where [old-engine] needs around five hours. While [old-engine] blocks search requests when updating its index, &zebra; can still answer search requests. [...] &zebra; supports incremental indexing which will speed up indexing even further. While the search time of [old-engine] varies from some seconds to some minutes depending how expensive the query is, &zebra; usually takes around one to three seconds, even for expensive queries. [...] &zebra; can search more than 100 times faster than [old-engine] and can process multiple search requests simultaneously I am very happy to see such nice software available under GPL.
Support You can get support for &zebra; from at least three sources. First, there's the &zebra; web site at , which always has the most recent version available for download. If you have a problem with &zebra;, the first thing to do is see whether it's fixed in the current release. Second, there's the &zebra; mailing list. Its home page at includes a complete archive of all messages that have ever been posted on the list. The &zebra; mailing list is used both for announcements from the authors (new releases, bug fixes, etc.) and general discussion. You are welcome to seek support there. Join by filling the form on the list home page.