Tree structure

Hi

I'm trying to determine the best way to represent a simple tree
structure (like a file/dir tree or a uri path). I guess that's done a
zillion times before; I just don't seem to be able to find the right
solution. I have one special request, that I'd like to find all
'shorter' paths, i.e. given 'a/b/c/d' it'll find

a
a/b
a/b/c
- but not
b
a/c
b/a

There are a number of options to test.

1. As strings
   There's no dedicated function (@>)
   WHERE clause should read something like 'a/b/c/d' LIKE column || '%',
which is both ugly and (I guess) non indexable
   Perhaps regex indexes would work, but not efficient and not optimal

2. As array of strings
   My favorite, would be elegant. A GIN index on the whole array would
make for fast performance
   Alas @> treats the arrays as a set, not an array
   WHERE col @> 'a/b/c/d' would find all of the above rows, including a,
a/c, b/a, etc.

3. ltree contrib
   The only option that actually works and uses index
   @> works as I want it to.
   But the single segments can only be alphanumeric and underscore
   ltree only supports GIST
   there's a length limit.

The last option is the one I'm using right now, but I hope that somebody
can point out where I'm wrong with regards to the other options, or tell
me that there is a better solution somewhere I didn't look.