NGD is used in the Average Fv NGD
(AFvNGD) score that indicates the semantic
distance between an entity and its FV terms. Note,
NGD is symmetric by definition, but searches with
Google™ are not (e.g., a search for "x y" often
yields different results from "y x"). This is tackled
by ordering the search terms (for instance, putting
the parent entity before a child entity). AFvNGD is
defined as follows: