for patents? Have you tried the USPTO Manual of Classification?
You ought to. ClassClarify can help.
is a software tool designed to aid researchers in using
the USPTO's Manual of Classification, the tool examiners
use to categorize patents.
ClassClarify graphically represents the manual and the relationships
amongst the classes, it's like a road map through the vast
landscape of prior art. Use it to understand how examiners
and industry analysts research prior art, and to perfect
your searching skills.
the fully functional demo version of the software today
and try it out; the licensed full version covers the whole
Manual ( some 400+ classes ) and can be ordered online here.