Category-key-words

Keywords are superior to directory hierarchies because things often fit into more than one category and there's more than one way of categorizing things.

But categories are kind of easier to browse without having to think too much.

Solution: each entry is entered using keywords, but the category system is generated automatically

-a top-level category for each key word
-the second level of each category has a sub-category for each other keyword existing in all its elements
-and so on

for example

object a, keywords b, c, e
object b, keywords d, e
object c, keywords q

hierarchy:

b        (object a)
  c      (object a)
    e    (object a)
  e      (object a)
    c    (object a)
c        (object a)
  b      (object a)
    e    (object a)
  e      (object a)
    b    (object a)
d        (object b)
  e      (object b)
e        (object a, object b)
  d      (object b)
  c      (object a)
    b    (object a)
  b      (object a)
    c    (object a)
q        (object c)

it might look like a really complicated hierarchy, but my theory is that it's not so complicated when you're collapsing and expanding branches at will from the top down.