# 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. If xDB is not set, the database is assumed not to have changed, which means if you only deal with one database you don't have to pass a useless extra parameter around.
DEFAULTOP
  default operator - values recognised `AND`, `and`, `OR`, `or`. As of version 1.3.0, the default is `AND` (previously it was `OR`). If you want to implement "match any words", set `DEFAULTOP=or`.
P
  query string to parse (may occur multiple times - if so, each will be parsed and the results combined with `OP_AND`).
P.PREFIX
  like `P`, but parsed with the default prefix set to PREFIX. For example, `P.A` will search the author by default.
xP
  terms from the previous parsed 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 appended to the value of the first non-empty `P` parameter, or used to build a query if there are no non-empty `P` parameters (used for topterms support when JavaScript isn't supported or is disabled).
X
  topterms to add to query (each term in a separate `X` parameter). If `ADD` is set, these will be appended to the value of the first non-empty `P` parameter, or used to build a query if there are no non-empty `P` parameters.
R
  relevant document(s) (multiple values separated by ".")
MORELIKE

  value is a numeric Xapian 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).

  Since Omega 1.4.18, MORELIKE queries are built with explicit `OR` operators if `DEFAULTOP` isn't `OR` (which it isn't by default since 1.3.0).

  Also since Omega 1.4.18, `MORELIKE` can be specified multiple times to find more documents like a specified set of documents. In earlier versions, only one of the values would be used in this case.

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 and N parameters are handled.

N

  negated general boolean filter terms (new in Omega 1.3.5 - older versions will just ignore any N parameters).

  See the overview document for details of how multiple B and N parameters are handled.

COLLAPSE
  value slot 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.
START.SLOT END.SLOT SPAN.SLOT

  One or more of these parameters can be specified for each SLOT to perform value-based date range filtering. A document must fall into all of the specified ranges to match.

  The values stored in the database in the specified SLOT need to be be in one of these formats with the format detected by looking at the length of the value bounds (each slot must use a single format, but different slots can use different formats):

  - YYYYMMDDHHMM (e.g. 200702142359)
  - YYYYMMDD (e.g. 20070214)
  - a raw 4 byte big-endian value representing a time_t (omindex adds the last modified time in value slot 0 in this format).

  SPAN.SLOT specifies the number of days either up to END.SLOT (if set), after START.SLOT (if set) or before today's date (if neither the start nor end are given) (if all three parameters are specified for the same SLOT then START.SLOT is ignored).

  If SPAN.SLOT is not specified:

  - START.SLOT specifies the start of the range in the format YYYY, YYYYMM, YYYYMMDD or YYYYMMDDHHMM. Default is the start of time.
  - END.SLOT specifies the end of the range in the format YYYY, YYYYMM, YYYYMMDD or YYYYMMDDHHMM. Default is the end of time.

  Added in Xapian 1.4.8 - older versions will just ignore these parameters.

DATEVALUE

  This is an older way to specify a value-based date range filter, which only allows one date range filter to be applied to each query. DATEVALUE specifies the value slot number to use. The format of the values stored in this slot in the database must be in one of the formats described above (YYYYMMDDHHMM, YYYYMMDD or a raw 4 byte big-endian time_t).

  One thing DATEVALUE is still useful for is that it supports an HTML form with a control (or controls) to select the date range and a control to select which date field to apply that to.

  Don't mix START.SLOT, END.SLOT and/or SPAN.SLOT with DATEVALUE on the same slot number.

  If DATEVALUE isn't set then START, END and SPAN will perform date filtering using an older approach based on D-, M-, and Y-prefixed terms. This approach can only filter to a granularity of one day, so only the YYYYMMDD part of START and END are used. Support for YYYY and YYYYMM in START and END for term-based date filtering was added in Xapian 1.4.8 - in earlier versions this failed with an error.

  Also instead of START/END defaulting to the start and end of time, they instead default to 1st January 1970 and today's date respectively. The term-based date range filtering also includes a special Dlatest term, which allows flagging a document as always current. There's no exact equivalent to this when using value-based date range filters, but giving such documents the maximum date value in the format being used provides a reasonable approximation to this feature.

START END SPAN
  like START.SLOT, END.SLOT and SPAN.SLOT but for value slot DATEVALUE, or for term-based date range filtering if DATEVALUE isn't set.
xFILTERS

  used to detect when the filters have changed from the previous search. Set this to `$html{$filters}` in your query template (`$filters` is a compact serialisation of filter-like settings).

  If xFILTERS is unset, the filters are assumed not to have changed (unlike xP). In Omega <= 1.2.21 and <= 1.3.3 they were always assumed to have changed in the situation, which meant you couldn't ever go past page 1 if you failed to set xFILTERS in your template. Now failing to set it means that the first page won't be forced in some cases where it probably should be.

THRESHOLD
  apply a percentage cut-off at the value given by this parameter (clipped to the range 0-100).

# Reordering parameters

SORT

  specifies one or more value slot numbers to order results by. The comparison used is a string compare of the unsigned byte values.

  The format of this parameter's value is a + or - specifying the direction of the sort followed by an unsigned integer value slot number. Normally + means an ascending sort (so the first result has the lowest value of the sort key) and - means a descending sort - however SORTREVERSE can change this (see below).

  The sort direction character was added in 1.3.5 - earlier versions defaulted to a descending sort (and for compatibility this is still the behaviour if you omit the + or -).

  Earlier versions also parsed the value as a signed integer and then cast it to unsigned, so beware of using updated templates with older versions.

  The ability to specify more than one value slot number was added in 1.4.1. Multiple slot specifiers are separated by zero or more whitespace and/or commas - e.g. SORT=+1-0+4, SORT=+1, -2, etc.

SORTREVERSE
  if non-zero, reverses the sort order specified by SORT. 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 ("X" by convention) 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

Omega does some special mangling of CGI parameter names which is intended to help with using image buttons, and also to enable providing nicer "alt" text in older browsers.

In the intervening decades HTML4 introduced the alt tag and CSS now provides cleaner ways to handle image buttons, so this mangling isn't as useful as it once was, but for now we've left it in place for compatibility.

## Image Buttons

When the user clicks on an image button <input type="image" name="PARAM">, the browser passes two CGI parameters PARAM.x and PARAM.y whose values report the x and y coordinates within the image that were clicked.

Image buttons allow for prettier navigation within search results, but what the browser passes is unhelpful so Omega does some special mangling of parameters with a .x or .y suffix:

> - PARAM.y is silently dropped
> - PARAM.x is truncated to PARAM

Then:

> - if the parameter name contains a space or (since 1.4.4) a tab, the value becomes everything after the first space/tab and the original value is ignored. (e.g.: [ 2 ].x=NNN becomes [=2 ]).
> - if the parameter name doesn't contain a space or (since 1.4.4) a tab:
>     - if the parameter name is entirely numeric, the name becomes # and the value becomes the parameter name. (e.g.: 2.x=NNN becomes #=2)
>     - otherwise, the value is replaced with the parameter name (e.g.: >.x=NNN becomes >=>)

Then general processing (as below) is applied.

## General

For ALL CGI parameters, the name is truncated at the first space or (since 1.4.4) a tab. So [ page two ]=2 becomes [=2.