Schematic representation of the backtracking heuristic to find most probable paths from a source concept s to a target t. (a) Assume a network with source and target concepts. For clarity, the nodes are ordered by their accessibility from s (leftmost nodes are most accessible, rightmost nodes least accessible). (b) As a first step in the backtracking process, we find the neighbors of the target t, leading in the direction of the source, that is, the neighbors of t with highest accessibility with respect to s. (c) The paths from the target are repeatedly expanded to include highly accessible nodes leading toward the source concept. Pruning of least probable paths keeps the growing set of paths to a workable size (not shown). (d) Most probable paths that arrive in the source (continuous lines) are considered as functional hypotheses linking the target to the source concept. Unfinished paths (dashed paths) continue being expanded until k paths between s and t have been found.
Liekens et al. Genome Biology 2011 12:R57 doi:10.1186/gb-2011-12-6-r57