# BIASDATE

The `BIASDATE` field specifier (case sensitive) allows you to boost the score of result documents by a specified percentage, based on how close the date in a specified field is to a specified date.

NOTE: You can optimize the speed of this field specifier by restricting the field to the `NumericDateType` property type.

## Format

    FieldText=BIASDATE{optimumDate,range,percentage}:yourFields

`optimumDate` | The date that the specified field must contain to increase or decrease the weight by the maximum percentage.
`range` | A positive value that defines the range, in seconds, of the specified `optimumDate`. If `yourFields` contain a value in the range (`optimum` - `range`) to (`optimum` + `range`), the weight is increased or decreased according to the specified `percentage`.
`percentage` | A percentage in the range 100 to -100. If the value of `yourFields` is in the specified `range`, the score of the result is increased or decreased according to how close the value is to the specified optimum. When `AbsWeight` is set to `true`, this value is the absolute value by which to boost the weight and it is not limited by +/- 100.
`yourFields` | Type one or more fields. A document has its score boosted if it contains one of these fields, and if this field contains a date that falls within the specified range of the optimum date. Separate multiple fields with colons (`:`). There must be no space before or after a colon.

You can use the following formats to specify your dates:

Date formats

Format | Explanation
--- | ---
`D+/M+/#YY+` | A date. For example, `1/3/05`, `23/12/1999`, `10/07/40`, or `8/5/2012`. If the year is a number less than 40, it is read as a year in the 2000s. If the year is a number between 40 and 99, it is read as a year in the 1900s. For example, `01/02/01` is read as 1 February 2001, and `01/03/40` is read as 1 March 1940. IDOL Server treats the date as a date in its local timezone.
`YYYY-MM-DD` | A date in ISO-8601 format. For example, `2017-05-12`
`HH:NN:SS D+/M+/#YY+` | A time and date. For example, `10:30:45 1/3/05`, `18:55:00 23/12/99`, `01:23:45 10/07/1940`, or `07:15:00 8/5/2012`. If the year is a number less than 40, it is read as a year in the 2000s. If the year is a number between 40 and 99, it is read as a year in the 1900s. For example, `01/02/01` is read as 1 February 2001, and `01/03/40` is read as 1 March 1940. IDOL Server treats the date as a date in its local timezone.
`YYYY-MM-DDTHH:NN:SSZ` `YYYY-MM-DDTHH:NN:SS±HHMM` | A date and time in ISO-8601 formats, with a time zone (either as a literal Z, or a four digit time zone offset). For example, `2017-05-02T12:45:00Z`, or `2017-05-02T12:45:00+0000`.
`HH:NN:SS D+/M+/#YY+ #ADBC` | A time and date with a time period. For example, `10:30:45 1/3/05 AD`, `18:55:00 23/12/99 CE`. For the time period, you can use `AD`, `CE`, `BC`, `BCE`, or any predefined list of EPOCH indicators. IDOL Server treats the date as a date in its local timezone.
`N` | A positive or negative number of days from the current date. For example, `–1` specifies yesterday's date, `0` specifies today's date, `1` specifies tomorrow's date, `2` specifies two days from now (the current date plus two), and so on.
`Ns` | A positive or negative number of seconds from now. For example, `–60s` specifies one minute ago, `–900s` specifies 15 minutes ago, `–3600s` specifies one hour ago and so on. `60s` specifies one minute from now, `900s` specifies 15 minutes from now, `3600s` specifies one hour from now, and so on.
`Ne` | Epoch seconds (seconds since 1 January 1970 UTC). For example, `1012345000e` specifies 22:56:40 on 29 January 2002 UTC.

NOTE: IDOL Server treats any date that does not have explicit timezone information as a date in the local timezone, both in the index and in your query parameters. This behavior might result in non-intuitive matches.

For example, epoch second values are always UTC. The value `1012345000e` matches times as 22:56:40 on 29 January 2002 UTC. If your local timezone is GMT-6, this query might match an indexed date value of 03:56:40 on 29 January 2002 (which corresponds to the same time UTC), because the indexed date is in your local timezone.

Similarly, if your query date is `03:56:40 29/01/2002`, this might match an indexed epoch seconds date of `1012345000`.

## Example

    FieldText=BIASDATE{01/12/2008,864000,10}:DATE

A document whose `DATE` field value is within a range of `10` days (`864000` seconds) either side of `1/12/2008` has its weight increased on a linear scale from `10%` if the date is `1/12/2008`, to `0%` if the date is `20/11/2008` or `11/12/2008`.

    FieldText=BIASDATE{01/12/2008,86400,-10}:DATE

A document whose `DATE` field value is within a range of `10` days (`864000` seconds) either side of `1/12/2008` has its weight decreased on a linear scale from `-10%` if the date is `1/12/2008`, to `0%` if the date is `20/11/2008` or `11/12/2008`.

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