1. A computer-implemented method of quantifying the similarity between a first node in a first electronic classification scheme and a second node in a second electronic classification scheme, the method comprising: finding a third node among those in the first electronic classification scheme, wherein a first product value of the inter-scheme similarity value between the second and third nodes and the intra-scheme similarity value between the first and third nodes is a maximum; finding a fourth node among those in the second electronic classification scheme, wherein a second product value of the inter-scheme similarity value between the first and fourth nodes and the intra-scheme similarity value between the second and fourth nodes is a maximum; and determining the maximum between the first and second product values, wherein the maximum represents a measure of similarity between the first and second nodes.