A More Concrete Ranking Model

$$R(Q, D) = \sum_i {g_i(Q) f_i(D)}$$

$f_i$ is some feature function that extracts a number from the document text.

$g_i$ is a similar feature function that extract a value from the query.

These two functions form a pair of feature functions. Each pair of functions is multiplied together, and the results from all pairs are added to create a final document score.