Link Relations: up/down vs parent/child vs ancestor/descendant etc.

Evening all,
I am busy designing a protocol for cloud computing[1] and want clients to be
able to discover children of a given resource in order to navigate a tree
structure. I had been considering defining a new "collection" link relation
but then found draft-divilly-atom-hierarchy<http://tools.ietf.org/html/draft-divilly-atom-hierarchy>
which
defines a "down" relation.

My concern is that the terms "up" and "down" are ambiguous in this context
and indeed we may end up defining [URI] relations for "up" and "down" as
state changes for network resources. Furthermore there has been come
commentary/confusion of late around the use of multiple attributes (e.g. "up
up up") and now seems as good a time as ever to clarify given we have the
link relation I-D and HTML 5 WD on the table at the IETF and W3C
respectively.

I wonder whether it would be possible to instead use "parent" and "child"
(for first generation relationships) or "ancestor" and "descendant" (for
more generic n-generation relationships, where n is specified as an
attribute like "level=2")? This is simple and self-describing and could
resolve the issue once and for all. Alternatively the terms could be
abbreviated to "asc" and "desc" respectively (as in "ascend" and "descend").

I also wonder whether "collection" isn't a bad idea anyway - consider a
resource describing a bookshelf where the collection consists of books.

Sam

1. http://www.occi-wg.org/