Term construction

Documents within an omega database are indexed by two types of terms: those used for a weighted search from a parsed query string (the CGI parameter P), and those used for boolean filtering (the CGI parameters B and N - the latter is a negated variant of 'B' and was added in Omega 1.3.5).

Boolean terms always start with a prefix which is an initial capital letter (or multiple capital letters if the first character is X) which denotes the category of the term (e.g. M for MIME type).

Parsed query terms may have a prefix, but don't always. Those from the body of the document in unstemmed form don't; stemmed terms have a Z prefix; terms from other fields have a prefix to indicate the field, such as S for the document title; stemmed terms from a field have both prefixes, e.g. ZS.

The "english" stemmer is used by default - you can configure this for omindex and scriptindex with --stemmer=LANGUAGE (use --stemmer=none to disable stemming, see omindex --help for the list of accepted language names). At search time you can configure the stemmer by adding $set{stemmer,LANGUAGE} to the top of your OmegaScript template.

The two term types are used as follows when building the query:

The P parameter is parsed using Xapian::QueryParser to give a Xapian::Query object denoted as P-terms below.

There are two ways that B and N parameters are handled, depending if the term-prefix has been configured as "non-exclusive" or not. The default is "exclusive" (and in versions before 1.3.4, this was how all B parameters were handled).

      [   OR   ]
     /    | ... \
B(F,1) B(F,2)...B(F,n)

      [   AND   ]
     /     | ... \
B(K,1) B(K,2)... B(K,m)

              [     AND     ]
             /       |  ...  \
            /                 \
      [   OR   ]               [   AND  ]
     /    | ... \             /    | ... \
B(F,1) B(F,2)...B(F,n)   B(K,1) B(K,2)...B(K,m)

      [       OR       ]
     / ... |     |  ... \
N(F,1)...N(F,n) N(K,1)...N(K,m)

                 [ AND_NOT ]
                /           \
               /             \
     [ FILTER ]             N-terms
      /      \
     /        \
P-terms      B-terms

Sites

Within a database, Omega supports multiple sites. These are recorded using boolean terms (see 'Term construction', above) to allow filtering on them.

Sites work by having all documents within them having a common base URL. For instance, you might have two sites, one for your press area and one for your product descriptions:

• http://example.com/press/index.html
• http://example.com/press/bigrelease.html
• http://example.com/products/bigproduct.html
• http://example.com/products/littleproduct.html

You could index all documents within http://example.com/press/ using a site of '/press', and all within http://example.com/products/ using '/products'.

Sites are also useful because omindex indexes documents through the file system, not by fetching from the web server. If you don't have a URL to file system mapping which puts all documents under one hierarchy, you'll need to index each separate section as a site.

An obvious example of this is the way that many web servers map URLs of the form <http://example.com/~<username>/> to a directory within that user's home directory (such as ~<username>/pub on a Unix system). In this case, you can index each user's home page separately, as a site of the form '/~<username>'. You can then use boolean filters to allow people to search only a specific home page (or a group of them), or omit such terms to search everyone's pages.

Note that the site specified when you index is used to build the complete URL that the results page links to. Thus while sites will typically want to be relative to the hostname part of the URL (e.g. '/site' rather than 'http://example.com/site'), you can use them to have a single search across several different hostnames. This will still work if you actually store each distinct hostname in a different database.

omindex operation

omindex is fairly simple to use, for example:

omindex --db default --url http://example.com/ /var/www/example.com

For a full list of command line options supported, see man omindex or omindex --help.

You must specify the database to index into (it's created if it doesn't exist, but parent directories must exist). You will often also want to specify the base URL (which is used as the site, and can be relative to the hostname - starts '/' - or absolute - starts with a scheme, e.g. 'http://example.com/products/'). If not specified, the base URL defaults to /.

You also need to tell omindex which directory to index. This should be either a single directory (in which case it is taken to be the directory base of the entire site being indexed), or as two arguments, the first being the directory base of the site being indexed, and the second being a relative directory within that to index.

For instance, in the example above, if you separate your products by size, you might end up with:

• http://example.com/press/index.html
• http://example.com/press/bigrelease.html
• http://example.com/products/large/bigproduct.html
• http://example.com/products/small/littleproduct.html

If the entire website is stored in the file system under the directory /www/example, then you would probably index the site in two passes, one for the '/press' site and one for the '/products' site. You might use the following commands:

$ omindex -p --db /var/lib/omega/data/default --url /press /www/example/press
$ omindex -p --db /var/lib/omega/data/default --url /products /www/example/products

If you add a new large products, but don't want to reindex the whole of the products section, you could do:

$ omindex -p --db /var/lib/omega/data/default --url /products /www/example/products large

and just the large products will be reindexed. You need to do it like that, and not as:

$ omindex -p --db /var/lib/omega/data/default --url /products/large /www/example/products/large

because that would make the large products part of a new site, '/products/large', which is unlikely to be what you want, as large products would no longer come up in a search of the products site. (Note that the --depth-limit option may come in handy if you have sites '/products' and '/products/large', or similar.)

omindex has built-in support for indexing HTML, PHP, text files, CSV (Comma-Separated Values) files, SVG, Atom feeds, and AbiWord documents. It can also index a number of other formats using external programs. Filter programs are run with CPU, time and memory limits to prevent a runaway filter from blocking indexing of other files.

The way omindex decides how to index a file is based around MIME content-types. First of all omindex will look up a file's extension in its extension to MIME type map. If there's no entry, it will then ask libmagic to examine the contents of the file and try to determine a MIME type.

The following formats are supported as standard (you can tell omindex to use other filters too - see below):

• HTML (.html, .htm, .shtml, .shtm, .xhtml, .xhtm)
• PHP (.php) - our HTML parser knows to ignore PHP code
• text files (.txt, .text)
• SVG (.svg)
• Compressed SVG (.svgz)
• CSV (Comma-Separated Values) files (.csv)
• PDF (.pdf) if pdftotext is available (comes with poppler or xpdf)
• PostScript (.ps, .eps, .ai) if ps2pdf (from ghostscript) and pdftotext (comes with poppler or xpdf) are available
• OpenOffice/StarOffice documents (.sxc, .stc, .sxd, .std, .sxi, .sti, .sxm, .sxw, .sxg, .stw) if unzip is available
• OpenDocument format documents (.odt, .ods, .odp, .odg, .odc, .odf, .odb, .odi, .odm, .ott, .ots, .otp, .otg, .otc, .otf, .oti, .oth) if unzip is available
• MS Word documents (.dot) if antiword is available (.doc files are left to libmagic, as they may actually be RTF (AbiWord saves RTF when asked to save as .doc, and Microsoft Word quietly loads RTF files with a .doc extension), or plain-text).
• MS Excel documents (.xls, .xlb, .xlt, .xlr, .xla) if xls2csv is available (comes with catdoc)
• MS Powerpoint documents (.ppt, .pps) if catppt is available (comes with catdoc)
• MS Office 2007 documents (.docx, .docm, .dotx, .dotm, .xlsx, .xlsm, .xltx, .xltm, .pptx, .pptm, .potx, .potm, .ppsx, .ppsm) if unzip is available
• Wordperfect documents (.wpd) if wpd2text is available (comes with libwpd)
• MS Works documents (.wps, .wpt) if wps2text is available (comes with libwps)
• MS Outlook message (.msg) if perl with Email::Outlook::Message and HTML::Parser modules is available
• MS Publisher documents (.pub) if pub2xhtml is available (comes with libmspub)
• MS Visio documents (.vsd, .vss, .vst, .vsw, .vsdx, .vssx, .vstx, .vsdm, .vssm, .vstm) if vsd2xhtml is available (comes with libvisio)
• Apple Keynote documents (.key, .kth, .apxl) if key2text is available (comes with libetonyek)
• Apple Numbers documents (.numbers) if numbers2text is available (comes with libetonyek)
• Apple Pages documents (.pages) if pages2text is available (comes with libetonyek)
• AbiWord documents (.abw, .awt)
• Compressed AbiWord documents (.zabw)
• Rich Text Format documents (.rtf) if unrtf is available
• Perl POD documentation (.pl, .pm, .pod) if pod2text is available
• reStructured text (.rst, .rest) if rst2html is available (comes with docutils)
• Markdown (.md, .markdown) if markdown is available
• TeX DVI files (.dvi) if catdvi is available
• DjVu files (.djv, .djvu) if djvutxt is available
• OpenXPS and XPS files (.oxps, .xps) if unzip is available
• Debian packages (.deb, .udeb) if dpkg-deb is available
• RPM packages (.rpm) if rpm is available
• Atom feeds (.atom)
• MAFF (.maff) if unzip is available
• MHTML (.mhtml, .mht) if perl with MIME::Tools is available
• MIME email messages (.eml) and USENET articles if perl with MIME::Tools and HTML::Parser is available
• vCard files (.vcf, .vcard) if perl with Text::vCard is available

If you have additional extensions that represent one of these types, you can add an additional MIME mapping using the --mime-type option. For instance, if your press releases are PostScript files with extension .posts you can tell omindex this like so:

$ omindex --db /var/lib/omega/data/default --url /press /www/example/press --mime-type posts:application/postscript

The syntax of --mime-type is 'ext:type', where ext is the extension of a file of that type (everything after the last '.'). The type can be any string, but to be useful there either needs to be a filter set for that type - either using --filter or --read-filters, or by type being understood by default:

You can specify * as the MIME sub-type for --filter, for example if you have a filter you want to apply to any video files, you could specify it using --filter 'video/*:index-video-file'. Note that this is checked right after checking for the exact MIME type, so will override any built-in filters which would otherwise match. Also you can't use arbitrary wildcards, just * for the entire sub-type. And be careful to quote * to protect it from the shell. Support for this was added in 1.3.3.

If there's no specific filter, and no subtype wildcard, then */* is checked (assuming the mimetype contains a /), and after that * (for any mimetype string). Combined with filter command true for indexing by meta-data only, you can specify a fall back case of indexing by meta-data only using --filter '*:true'. Support for this was added in 1.3.4.

There are also two special values that can be specified instead of a MIME type:

• ignore - tells omindex to quietly ignore such files
• skip - tells omindex to skip such files

By default no extensions are marked as "skip", and the following extensions are marked as "ignore":

• a
• adm
• bin
• com
• css
• cur
• dat
• db
• dll
• dylib
• exe
• fon
• ico
• jar
• js
• lib
• lnk
• msi
• msp
• o
• obj
• pyc
• pyd
• pyo
• so
• sqlite
• sqlite-journal
• sqlite3
• tmp
• ttf

If you wish to remove a MIME mapping, you can do this by omitting the type - for example if you have .dot files which are inputs for the graphviz tool dot, then you may wish to remove the default mapping for .dot files and let libmagic be used to determine their type, which you can do using: --mime-type=dot: (if you want to ignore all .dot files, instead use --mime-type=dot:ignore).

The lookup of extensions in the MIME mappings is case sensitive, but if an extension isn't found and includes upper case ASCII letters, they're converted to lower case and the lookup is repeated, so you effectively get case insensitive lookup for mappings specified with a lower-case extension, but you can set different handling for differently cased variants if you need to.

You can add support for additional MIME content types (or override existing ones) using the --filter and/or --read-filters options to specify a command to run. At present, this command needs to produce output in either HTML, SVG, or plain text format (as of 1.3.3, you can specify the character encoding that the output will be in; in earlier versions, plain text output had to be UTF-8). Support for SVG output from external commands was added in 1.4.8.

As of 1.3.3, the command can include certain placeholders which are substituted by omindex:

• Any %f in this command will be replaced with the filename of the file to extract (suitably escaped to protect it from the shell, so don't put quotes around %f).

  If you don't include %f in the command, then the filename of the file to be extracted will be appended to the command, separated by a space.

• Any %t in this command will be replaced with a filename in a temporary directory (suitably escaped to protect it from the shell, so don't put quotes around %t). The extension of this filename will reflect the expected output format (either .html, .svg or .txt). If you don't use %t in the command, then omindex will expect output on stdout (prior to 1.3.3, output had to be on stdout).

• %% can be used should you need a literal % in the command.

For example, if you'd prefer to use Abiword to extract text from word documents (by default, omindex uses antiword), then you can pass the option --filter=application/msword:'abiword --to=txt --to-name=fd://1' to omindex.

Another example - if you wanted to handle files of MIME type application/octet-stream by running them through strings -n8, you can pass the option --filter=application/octet-stream:'strings -n8'.

A more complex example: to process .foo files with the (fictional) foo2utf16 utility which produces UTF-16 text but doesn't support writing output to stdout, run omindex with -Mfoo:text/x-foo -Ftext/x-foo,,utf-16:'foo2utf16 %f %t'.

A less contrived example of the use of --filter makes use of LibreOffice, via the unoconv script, to extract text from various formats. First you need to start a listening instance (if you don't, unoconv will start up LibreOffice for every file, which is rather inefficient) - the & tells the shell to run it in the background:

unoconv --listener &

Then run omindex with options such as --filter=application/msword,html:'unoconv --stdout -f html' (you'll want to repeat this for each format which you want to use LibreOffice on).

If you specify false as the command in --filter, omindex will skip files with the specified MIME type. (As of 1.2.20 and 1.3.3 false is explicitly checked for; in earlier versions this will also work, at least on Unix where false is a command which ignores its arguments and exits with a non-zero status).

If you specify true as the command in --filter, omindex won't try to extract text from the file, but will index it such that it can be searched for via metadata which comes from the filing system (filename, extension, mime content-type, last modified time, size). (As of 1.2.22 and 1.3.4 true is explicitly checked for; in earlier versions this will also work, at least on Unix where true is a command which ignores its arguments and exits with a status zero).

If you know of a reliable filter which can extract text from a file format which might be of interest to others, please let us know so we can consider including it as a standard filter.

The --duplicates option controls how omindex handles documents which map to a URL which is already in the database. The default (which can be explicitly set with --duplicates=replace) is to reindex if the last modified time of the file is newer than that recorded in the database. The alternative is --duplicates=ignore, which will never reindex an existing document. If you only add documents, this avoids the overhead of checking the last modified time. It also allows you to prioritise adding completely new documents to the database over updating existing ones.

By default, omindex will remove any document in the database which has a URL that doesn't correspond to a file seen on disk - in other words, it will clear out everything that doesn't exist any more. However if you are building up an omega database with several runs of omindex, this is not appropriate (as each run would delete the data from the previous run), so you should use the --no-delete option. Note that if you choose to work like this, it is impossible to prune old documents from the database using omindex. If this is a problem for you, an alternative is to index each subsite into a different database, and merge all the databases together when searching.

--depth-limit allows you to prevent omindex from descending more than a certain number of directories. Specifying --depth-limit=0 means no limit is imposed on recursion; --depth-limit=1 means don't descend into any subdirectories of the start directory.

HTML Parsing

The document <title> tag is used as the document title. Metadata in various <meta> tags is also understood - these values of the name parameter are currently handled when found:

• author, dcterms.creator, dcterms.contributor: author(s)
• created, dcterms.issued: document creation date
• classification: document topic
• keywords, dcterms.subject, dcterms.description: indexed as extra document text (but not stored in the sample)
• description: by default, handled as keywords, as of Omega 1.4.4. If omindex is run with --sample=description, then this is used as the preferred source for the stored sample of document text (HTML documents with no description fall back to a sample from the body; if description occurs multiple times then second and subsequent are handled as keywords). In Omega 1.4.2 and earlier, --sample wasn't supported and the behaviour was as if --sample=description had been specified. In Omega 1.4.3, --sample was added, but the default was --sample=description (contrary to the intended and documented behaviour) - you can use --sample=body with 1.4.3 and later to store a sample from the document body.

The HTML parser will look for the 'robots' META tag, and won't index pages which are marked as noindex or none, for example any of the following:

<meta name="robots" content="noindex,nofollow">
<meta name="robots" content="noindex">
<meta name="robots" content="none">

The omindex option --ignore-exclusions disables this behaviour, so the files with the above will be indexed anyway.

Sometimes it is useful to be able to exclude just part of a page from being indexed (for example you may not want to index navigation links, or a footer which appears on every page). To allow this, the parser supports "magic" comments to mark sections of the document to not index. Two formats are supported - htdig_noindex (used by ht://Dig) and UdmComment (used by mnoGoSearch):

Index this bit <!--htdig_noindex-->but <b>not</b> this<!--/htdig_noindex-->

<!--UdmComment--><div>Boring copyright notice</div><!--/UdmComment-->

Boolean terms

omindex will create the following boolean terms when it indexes a document:

E

Extension of the file (e.g. Epdf) [since Omega 1.2.5]

T

MIME type

J

The base URL, omitting any trailing slash (so if the base URL was just /, the term is just J). If the resulting term would be > 240 bytes, it's hashed in the same way an U prefix terms are. Mnemonic: the Jumping-off point. [since Omega 1.3.4]

H

hostname of site (if supplied - this term won't exist if you index a site with base URL '/press', for instance). Since Omega 1.3.4, if the resulting term would be > 240 bytes, it's hashed in the same way as U prefix terms are.

P

path terms - one term for the directory which the document is in, and for each parent directories, with no trailing slashes [since Omega 1.3.4 - in earlier versions, there was just one P term for the path of site (i.e. the rest of the site base URL) - this will be amongst the terms Omega 1.3.4 adds]. Since Omega 1.3.4, if the resulting term would be > 240 bytes, it's hashed in the same way as U prefix terms are.

U

full URL of indexed document - if the resulting term would be > 240 bytes, a hashing scheme is used to avoid overflowing Xapian's term length limit.

By default the following additional boolean terms are added to documents:

D

date (numeric format: YYYYMMDD)

date can also have the magical form "latest" - a document indexed by the term Dlatest matches any date-range without an end date. You can index dynamic documents which are always up to date with Dlatest and they'll match as expected. (If you use sort by date, you'll probably also want to set the value containing the timestamp to a "max" value so dynamic documents match a date in the far future).

M

month (numeric format: YYYYMM)

Y

year (four digits)

These support an older approach to date filtering. We now recommend using a value slot for this instead, as it is more flexible (e.g. it supports multiple date fields) and generally performs better.

Since Omega 1.4.22 these can be disabled with the omindex command line option --no-date-terms; Omega 1.5.0 will stop adding these by default, with --date-terms to enable them (also supported 1.4.22).

omega configuration

Most of the omega CGI configuration is dynamic, by setting CGI parameters. However some things must be configured using a configuration file. The configuration file is searched for in various locations:

• Firstly, if the "OMEGA_CONFIG_FILE" environment variable is set, its value is used as the full path to a configuration file to read.
• Next (if the environment variable is not set, or the file pointed to is not present), the file "omega.conf" in the same directory as the Omega CGI is used.
• Next (if neither of the previous steps found a file), the file "${sysconfdir}/omega.conf" (e.g. /etc/omega.conf on Linux systems) is used.
• Finally, if no configuration file is found, default values are used.

The format of the file is very simple: a line per option, with the option name followed by its value, separated by a whitespace. Blank lines are ignored. If the first non-whitespace character on a line is a '#', omega treats the line as a comment and ignores it.

The current options are:

• database_dir: the directory containing all the Omega databases
• template_dir: the directory containing the OmegaScript templates
• log_dir: the directory which the OmegaScript $log command writes log files to
• cdb_dir: the directory which the OmegaScript $lookup command looks for CDB files in

The default values (used if no configuration file is found) are:

database_dir /var/lib/omega/data
template_dir /var/lib/omega/templates
log_dir /var/log/omega
cdb_dir /var/lib/omega/cdb

Note that, with apache, environment variables may be set using mod_env, and with apache 1.3.7 or later this may be used inside a .htaccess file. This makes it reasonably easy to share a single system installed copy of Omega between multiple users.

Supplied Templates

The OmegaScript templates supplied with Omega are:

• query - This is the default template, providing a typical Web search interface.
• topterms - This is just like query, but provides a "top terms" feature which suggests terms the user might want to add to their query to obtain better results.
• godmode - Allows you to inspect a database showing which terms index each document, and which documents are indexed by each term.
• opensearch - Provides results in OpenSearch format (for more details see http://www.opensearch.org/).
• xml - Provides results in a custom XML format.
• emptydocs - Shows a list of documents with zero length. If CGI parameter TERM is set to a non-empty value, then only documents indexed by that given term are shown (e.g. TERM=Tapplication/pdf to show PDF files with no text); otherwise all zero length documents are shown.

There are also "helper fragments" used by the templates above:

• inc/anyalldropbox - Provides a choice of matching "any" or "all" terms by default as a drop down box.
• inc/anyallradio - Provides a choice of matching "any" or "all" terms by default as radio buttons.
• toptermsjs - Provides some JavaScript used by the topterms template.

Document data construction

This is only useful if you need to inject your own documents into the database independently of omindex, such as if you are indexing dynamically-generated documents that are served using a server-side system such as PHP or ASP, but which you can determine the contents of in some way, such as documents generated from reasonably static database contents.

The document data field stores some summary information about the document, in the following (sample) format:

url=<baseurl>
sample=<sample>
caption=<title>
type=<mimetype>

Further fields may be added (although omindex doesn't currently add any others), and may be looked up from OmegaScript using the $field{} command.

As of Omega 0.9.3, you can alternatively add something like this near the start of your OmegaScript template:

$set{fieldnames,$split{caption sample url}}

Then you need only give the field values in the document data, which can save a lot of space in a large database. With the setting of fieldnames above, the first line of document data can be accessed with $field{caption}, the second with $field{sample}, and the third with $field{url}.

Stopword List

At search time, Omega uses a built-in list of stopwords, which are:

a about an and are as at be by en for from how i in is it of on or that the
this to was what when where which who why will with you your