This document explains the format used for specifying the
"Min Number Should Match" criteria of the BooleanQuery objects built by the
Explanation of Concept: "Min Number Should Match"
Specification strings may have the following formats...
A positive integer, indicating a fixed value regardless of the
number of optional clauses.
A negative integer, indicating that the total number of optional clauses,
minus this number should be mandatory.
A percentage, indicating that this percent of the total number of
optional clauses are necessary. The number computed from the
percentage is rounded down and used as the minimum.
A negative percentage, indicating that this percent of the total
number of optional clauses can be missing. The number computed from the
percentage is rounded down, before being subtracted from the total
to determine the minimum.
A positive integer, followed by the less-than symbol, followed
by any of the previously mentioned specifiers is a conditional
specification. It indicates that if the number of optional clauses is
equal to (or less than) the integer, they are all required, but
if it's greater than the integer, the specification applies.
In this example: if there are 1 to 3 clauses they are all required,
but for 4 or more clauses only 90% are required.
Multiple conditional specifications can be separated by spaces,
each one only being valid for numbers greater than the one before it.
In this example: if there are 1 or 2 clauses both are required,
if there are 3-9 clauses all but 25% are required, and if there
are more than 9 clauses, all but three are required.
A few important notes...
When dealing with percentages, negative values can be used to get
different behavior in edge cases. 75% and -25% mean the same thing
when dealing with 4 clauses, but when dealing with 5 clauses 75% means
3 are required, but -25% means 4 are required.
If the calculations based on the specification determine that no
optional clauses are needed, the usual rules about BooleanQueries
still apply at search time (a BooleanQuery containing no required
clauses must still match at least one optional clause)
No matter what number the calculation arrives at,
a value greater than the number of optional clauses, or a value less than
1 will never be used. (ie: no matter how low or how high the result of the
calculation result is, the minimum number of required matches will never
be lower than 1 or greater than the number of clauses.