Figure 9

Procedure of recursive re-ranking. A recursive re-ranking algorithm is called for the phase of re-ranking in the section of the factor analysis based algorithm. The recursive division divides the passages into the base cases, according to the sorted term association, which is very similar to a binary tree. For example, the factor analysis based model gives a ranking list of terms as {T₁, T₂, T₃} for re-ranking. The baseline results are then first re-ranking by T₁, where $P_1^1$ are results containing T₁ and $P_2^1$ are results not containing T₁. Second, $P_1^1$ and $P_2^1$ are recursively re-ranked by T₂. $P_1^2$ are the results containing T₂ and T₁, while $P_2^2$ are those not containing T₂ but containing T₁. $P_3^2$ are the results containing T₂ but not containing T₁, while $P_4^2$ are those not containing T₂ and T₁. Similarly, $P_1^2$(i = {1, 2, 3, 4} are re-ranked by T₃ at the third step.