The Jaro-Winkler distance measures string similarity represented as a real number between 0 and 1. The value 0 corresponds to no similarity, and 1 corresponds to an identical match.
The algorithm behind the function comes from the following mathematical formula presented in the Wikipedia article about the Jaro-Winkler distance http://en.wikipedia.org/wiki/Jaro%E2%80%93Winkler_distance:
In the preceding formula, the following are the representations of the variables used:
s1 is the first string.
s2 is the second string.
m is the number of identical characters within a distance of at the most half the length of the longer string. These are called matching characters.
t is half the number of matching characters that are not in the same index. In other words, it is half the number of transpositions.