Zhang et al. (2014) evaluate this relevance by propagating relevance weight from sd-nodes to t b iteratively. After convergence, the relevance weight of t b will be treated as the final relevance to D. There are in total n × n pairs of nodes, and their p(i, j) are stored in a matrix P.<cite> Zhang et al. (2014)</cite> use W = (w 1 , w 2 , . . . , w n ) to denote the relevance weights of nodes, where w i indicates the relevance of t i to D. At the beginning, each w i of bk-nodes is initialized to 0, and each that of sd-nodes is initialized to its importance to D. Then W is updated to W after every iteration according to Formula 3. They keep updating the weights of both sd-nodes and bk-nodes until convergence and do not distinguish them explicitly.