2.1.10 XRANK Operator
The XRANK operator allows dynamic control over ranking. It boosts the dynamic rank of items based on certain term occurrences without changing which items that match the query.
An XRANK expression MUST contain one expression operand that MUST be matched (the preceding operand, called match expression), and one expression operand (the subsequent operand, called rank expression) that contributes only to dynamic rank and MUST NOT affect which items are returned as matches. The matching rank expression will add a boost value to the item’s total rank.
The named parameters in the following table are valid with the XRANK operator:
Named parameter |
Default value |
Description |
---|---|---|
cb |
0 |
Specifies the constant boost, corresponds to a in the XRANK formula (see section 2.1.10.1). |
rb |
0 |
Specifies the range boost, corresponds to b in the XRANK formula. This factor is multiplied with the range of rank values in the result set. |
pb |
0 |
Specifies the percentage boost, corresponds to c in the XRANK formula. This factor is multiplied with the item’s own rank compared to the minimum value in the result set. |
avgb |
0 |
Specifies the average boost, corresponds to d in the XRANK formula. This factor is multiplied with the average rank value of the result set. |
stdb |
0 |
Standard deviation boost, corresponds to e in the XRANK formula. This factor is multiplied with the standard deviation of the rank values of the result set. |
nb |
0 |
Normalized boost, corresponds to f in the XRANK formula. This factor is multiplied with the product of the variance and average score of the rank values of the result set. |
n |
0 |
Number of results to compute statistics from. This parameter does not affect the number of results to which the XRANK contributes; it is just a means to exclude "irrelevant" documents from the statistics calculations. |
At least one of the parameters cb, rb, pb, avgb, stdb, or nb MUST be specified.