I'd never heard of these terms before. After some searching and finding papers
which describe what LOUDS (level order unary degree sequence) is, I realize I
use these (in a trivial form). I used the term "hierarchical bitfield", and
over the years I've tried searching for the technique using various terms --
with no success. I must say I never would have guessed "level order unary
degree sequence". :)
So, thank you for finally providing a name, and a means to find other work
using this structure. My uses are in games: succinctly representing
hierarchical data in a manner which I can do fast bitmatches. Unfortunately, I
don't have a nice library for building and working with these datastructures,
as my uses are fairly limited: trees that can be encoded within 64 bits.
Hopefully someone out there knows of a library in OCaml, but if not, the
"bitstring" library might be a useful building block... or, of course, the
option of binding to a C library.
Good luck! Sorry I couldn't be more helpful, while you've helped me by asking
a question.