I devised the category scheme very roughly according to the way universities divide up academic departments. I tried, above all, to be exhaustive; if there is some area of human knowledge that cannot be placed in this category scheme, I'd like to know. The supercategories ("FoundationalDisciplines," "NaturalSciences," etc.) are all reasonably coherent concepts, and in most cases it's clear enough that a category definitely belongs in one supercategory rather than another.
On the whole, I think that as a category scheme it is a lot more coherent than, say, the DeweyDecimalSystem? or the LibraryOfCongressClassificationScheme?. But of course others may differ. Feel free to devise your own category scheme and place it on the CategorySchemes page! -- LarrySanger
Science includes the principles behind things, but technology includes their uses. A lot of topics will straddle the two, but for a top-level classification I don't think there's a problem. I do agree, though, that there are way to many top-level nodes. Off the top of my head, I would propose a different system:
Understanding the way the world works - PhiloSophy, MathematicsAndStatistics, NaturalSciences Understanding what's actually in it - BiologicalSciences? (?), HiStory?, GeoGraphy? Making stuff for practical use - TechnologY Making stuff for its own ends - ArtsAndEntertainment?