# CGI parameters to Omega

In addition to the parameters listed here, all other parameters are retained. Arbitrary CGI parameters may be read with the $cgi{PARAM} and $cgilist{PARAM} OmegaScript commands.

Note that all CGI parameters are modified by Omega before they become part of $cgilist{} - see the section at the end for details.

# Main query parameters

DB
  database name. If the DB parameter is specified more than once, each value is used to allow searching over multiple databases. Also, the value of each DB parameter may be a list of database names separated by "/". If no DB parameters are specified, then the database name defaults to `default`. If you want to search over a combination of databases by default then you can make the `default` database a stub database file - see the "Overview" document in xapian-core for details of the format.
xDB
  database(s) used for last query (separated by / if appropriate). If the database(s) used change then relevance judgements are discarded and the first page of matches is shown.
DEFAULTOP
  default operator - values recognised "AND", "and", "OR", "or". Default: OR. If you want to implement "match all words", set DEFAULTOP=AND.
P
  probabilistic query (may occur multiple times).
xP
  terms from previous probabilistic query - used to decide if this is a fresh query (in which case relevance judgements are discarded and the first page of matches is shown), an extended query (in which case the first page of matches is shown), or an unchanged query.
ADD
  if present, any X parameters are added to the probabilistic query (used for topterms support when JavaScript isn't supported or is disabled).
X
  topterms to add to query.
R
  relevant document(s) (multiple values separated by ".")
MORELIKE
  value is a document id to return similar pages to, or a term name (which will be looked up and the document id of the first document it indexes will be used - this allows a MORELIKE query based on the unique id from an external database)
RAWSEARCH
  when set to non-zero value, this prevents TOPDOC being snapped to a multiple of HITSPERPAGE. Normally we snap TOPDOC like this so that things work nicely if HITSPERPAGE is in a picker or on radio buttons. If we're postprocessing the output of omega and want variable sized pages, this is unhelpful.
MINHITS
  can be set to look for more matches than would otherwise be looked for to you can be sure how many more consecutive pages will definitely be needed to show results. By default omega asks for one hit more than the last one displayed on this page (so we know for sure if there is a next page or not). If MINHITS is set, we ask for at least MINHITS matches from the start of the current page - you can think of MINHITS as defaulting to (HITSPERPAGE + 1).

# Filtering parameters

B
  general boolean filter terms. See the overview document for details of how multiple B parameters are handled.
COLLAPSE
  value number to use for removing duplicate documents. Additional documents in the MSet with the same value will be removed from the MSet. $value{$cgi{COLLAPSE}} can be used to access the actual value for each hit.
DATEVALUE
  value number to use for date range filtering. If this isn't set then date filtering will use the older approach based on D-, M-, and Y-prefixed terms. The values must be of the format YYYYMMDDHHMM (e.g. 200702142359), YYYYMMDD (e.g. 20070214), or a raw 4 byte big-endian value representing a time_t (omindex adds this as value 0 by default).
SPAN
  filter on this number of days up to END (if set), or after START (if set), or before today's date (otherwise).
START
  start of date range, in the format YYYYMMDD (defaults to 1st January 1970). If value-based date ranges are used (see DATEVALUE parameter) then the format YYYYMMDDHHMM is also valid.
END
  end of date range, in the format YYYYMMDD (defaults to today's date). If value-based date ranges are used (see DATEVALUE parameter) then the format YYYYMMDDHHMM is also valid.
xFILTERS
  used to spot when the filters have changed from the previous search. Set this to $html{$filters} in your query template ($filters is a compact serialisation of the currently set B filters, date-range filters, COLLAPSE, and DEFAULTOP).
THRESHOLD
  apply a percentage cut-off at the value given by this parameter (clipped to the range 0-100).

# Reordering parameters

SORT
  reorder results by this value number (greater values are better). The comparison used is a string compare.
SORTREVERSE
  if non-zero, reverse the sort order so that lower values are better. This parameter has no effect unless SORT is also specified.
SORTAFTER
  if non-zero, order results by relevance, only sorting by value to order values with the same relevance score. This parameter has no effect unless SORT is also specified.
DOCIDORDER
  set the ordering used when a comparison ends up being by docid (i.e. two documents with equal relevance and/or values). By default (if DOCIDORDER isn't set or is empty) this puts them in ASCENDING order (the lowest document id ranks highest). If DOCIDORDER is specified and non-empty it can begin with "D" for DESCENDING order, "A" for ASCENDING order or any other character for DONT_CARE (the Xapian database backend will use whichever order is most efficient). Any characters after the first are ignored.

# Display parameters and navigation

FMT
  name of page format to use (may not contain `..`).
HITSPERPAGE
  hits per page (integer) - clipped to range 10-1000.
TOPDOC
  first document to display (snapped to multiple of HITSPERPAGE if RAWSEARCH is not set)

If a parameter named '<' or '>' exists, Omega will go to the previous or next results page (based on the value of TOPDOC), respectively. If not, and a parameter named '[' or '#' exists, it will jump to the page number given by that parameter (trailing junk after the number is ignored). (See the section below on modification of CGI parameters to see how this works.)

This means that <input type='image' .../> form buttons can have names of the form '[ 3 ]', which looks nice in lynx, for tooltips, and so on. For text-only links, you really need to write out the entire GET parameters and use a normal anchor.

# Modification of CGI parameters

For an image button, two CGI parameters are passed from the HTML client, of the form "PARAM.x" and "PARAM.y" (the x and y coordinates within the image that were clicked).

The PARAM part of the parameters are taken from the value attribute of the <input> element that specified that image button in the HTML page. We regularly use image buttons to provide pretty navigation within search results (they are part of a form because it is easier to treat more or less all of Omega as a single form, rather than generating very long GET requests for every button on the results page), so Omega does some mangling of these parameters:

> - PARAM.y is silently dropped

> - PARAM.x is truncated to PARAM

> - if PARAM contains a space (the CGI parameter name, not the value):
>     - the value becomes everything after the first space; the original value is dropped. (e.g.: [ 2 ].x=NNN becomes [=2 ])
>   otherwise:
>     - if PARAM is entirely numeric, the name becomes '#' and the value becomes PARAM. (e.g.: 2.x=NNN becomes #=2)
>     - if PARAM is not entirely numeric, the value is copied from PARAM (e.g.: >.x=NNN becomes >=>)

Then, for ALL CGI parameters, the name is truncated at the first space. So [ page two ]=2 becomes [=2.