rough concept; S is refining operation including edges
directed from parent node to child node, and edges linked
by lower approximation extension from rough concept to
precise concept; P is a positive contact which is used to
represent relationship between edges; Gr and Sr represent
the edges in imprecise rules and the edges between
precise concepts connected by upper approximate
extension respectively; “–” is meaningless operation.
Such as a path: G S P Gr Sr, the semantic
distance is 2 + 3.5 + 4 + 5 = 14.5.