Graphical illustration of the algorithm. Nodes in the higher level graph and sub-graphs are shown by black and green circles, respectively. Root nodes of sub-graphs are shown by solid green circles and are equivalent to the corresponding higher level node. Terms A and B belong to the same sub-graph, therefore the semantic similarity score between them will be computed based on their common ancestor term 'Cytoplasm' (solid green). Terms B and C belong to different sub-graphs, therefore their semantic similarity score will be computed based on the common ancestor term 'Intracellular'.