Noteworthy features of Xapian include:
- Free Software/Open Source - licensed under the GPL.
- Supports Unicode 9.0 (including codepoints beyond the BMP), and stores
indexed text in UTF-8.
portable - runs on Android, Linux, macOS, FreeBSD, NetBSD, OpenBSD,
Solaris, HP-UX, AIX and probably other Unix platforms; as well as
Microsoft Windows and OS/2.
- Written in C++, with bindings allowing use from
many other languages.
- Ranked search (so the most relevant documents are more likely to come near
the top of the results list) with built-in support for multiple models
from the Probabilistic, Divergence from Randomness, and Language Modelling
families of weighting models. Custom user-supplied weighting models are
- Relevance feedback - given one or more documents, Xapian can suggest the
most relevant index terms to expand a query, suggest related documents,
categorise documents, etc.
- Phrase and proximity searching - users can search for words
occurring in an exact phrase or within a specified number of words,
either in a specified order, or in any order.
- Full range of structured boolean search operators ("stock NOT market",
etc). The results of the boolean search are ranked by the weighting
model, and boolean filters can also be applied (which don't themselves
contribute to a document's weight).
- Supports stemming of search terms (e.g. a search for "football" would
match documents which mention "footballs" or "footballer"). This helps
to find relevant documents which might otherwise be missed.
Snowball stemmers are currently
included for Arabic, Armenian, Basque, Catalan,
Danish, Dutch, English, Finnish, French, German, Hungarian, Indonesian,
Irish, Italian, Lithuanian, Nepali, Norwegian, Portuguese, Romanian,
Russian, Spanish, Swedish, Tamil and Turkish.
- Wildcard search is supported (e.g. "xap*").
- Synonyms are supported, both explicitly (e.g. "~cash") and as an automatic
form of query expansion.
- Dynamically generated snippets from matching documents can be generated,
with matching words, phrases and wildcards highlighted.
- Xapian can suggest spelling corrections for user supplied queries. This
is based on words which occur in the data being indexed, so works even for
words which wouldn't be found in a dictionary (e.g. "xapian" would be
suggested as a correction for "xapain").
- Faceted search is supported.
- Supports database files > 2GB - essential for
scaling to large document collections.
- Platform independent data formats - you can build a database on one
machine and search it on another.
- Allows simultaneous update and searching. New documents become searchable
As well as the library, we supply a number of small example programs, and
a larger application - an indexing and CGI search application called Omega:
- The indexer supplied can index HTML, PHP, PDF, PostScript,
Microsoft Outlook saved messages,
Word Perfect, AbiWord, RTF, DVI, Perl POD documentation, CSV, SVG,
reStructured text, markdown, MAFF, MHTML, ATOM feeds, dejavu, RFC822 mail
messages (.eml), RPM packages, Debian packages, and plain text.
Adding support for indexing other formats is easy where conversion filters
are available. This indexer works using the
filing system, but we also provide a script to allow the htdig web
crawler to be hooked in, allowing remote sites to be searched using Omega.
- You can also index data from any SQL or other RDBMS supported by the
Perl DBI module.
That includes MySQL, PostgreSQL, SQLite, Oracle, DB2, MS SQL, LDAP, and ODBC.
- CGI search front-end supplied with highly customisable appearance. This
can also be customised to output results in JSON, XML or CSV, which is useful
if you just want raw search results which you can process in your own page
layout code for dynamically generated pages, or for integrating search into an