But, the fuzziness isn't necessarily a flaw at all; having more and less typical examples of a category has shown itself to be pretty handy, since we can use the level-of-typicalness to influence how confidently we can make correlations ("birds lay eggs and have feathers and fly, X has feathers but doesn't fly, so I'm only pretty sure it lays eggs").

I think that would be a valuable feature in a fact database.