1. A computer program product comprising: a tangible storage medium readable by a processing circuit and storing instructions for execution by the processing circuit to perform a method comprising: accessing a graphical model in a data store, the graphical model comprising a plurality of nodes, the nodes connected by edges having edge strengths representing a degree of relation between the nodes; receiving a target relation strength for a pair of nodes in the graphical model; determining an edge strength of an edge in a direct path between the pair of nodes, the determining comprising: traversing, in the graphical model, one or more paths other than the direct path between the pair of nodes; estimating a cumulative strength of the traversed paths; and calculating the edge strength for the edge in the direct path based on the cumulative strength of the traversed paths and the target relation strength, the calculating comprising: subtracting the cumulative strength from the target relation strength; and setting the edge strength of the edge in the direct path to the result of the subtracting based on the result being a positive number; and assigning the calculated edge strength to the edge in the direct path between the two nodes.